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+# Changelog
+
+All notable changes to baikai are recorded here.
+
+The format follows [Keep a Changelog](https://keepachangelog.com/en/1.1.0/), and
+this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
+
+## [Unreleased]
+
+## [baikai 0.6.0.0] - 2026-08-28
+
+### Added
+
+- `baikai`: `Baikai.ThinkingLevel.parseThinkingLevel :: Text -> Maybe
+  ThinkingLevel` and `Baikai.Evidence.parseEvidenceStrength :: Text -> Maybe
+  EvidenceStrength`, each beside its renderer. Three hand-copied tables — the
+  evidence schema's level parser, `baikai-agent`'s KDL `effort` decoder, and its
+  `--require-evidence` parser — now read them instead, so a level or strength
+  added later cannot be added in one place and missed in three. (REV-2 G.6.)
+
+- `baikai`: `Baikai.Agent.AgentRunResult` exports its selectors (`provider`,
+  `exitCode`, `stdout`, `stderr`, `duration`). It exported neither them nor its
+  constructor, so a consumer without generic-lens could not read a run's exit
+  code at all. (REV-2 G.6.)
+
+- `baikai`: `Baikai.Api.normaliseApi :: Api -> Api`, which collapses a `Custom`
+  tag that spells a built-in API onto that constructor. The registry applies it
+  to the key it stores and to the tag it is asked for, so a handler registered
+  under `Custom "anthropic-messages"` answers a model tagged `AnthropicMessages`
+  and the reverse; the two used to be separate entries and dispatch depended on
+  which spelling the model happened to carry. Derived `Eq`/`Ord` on `Api` are
+  deliberately unchanged: altering them would silently rearrange every
+  `Map Api` a consumer holds. (REV-2 G.4.)
+
+- `baikai`: `Baikai.Header`, a new module exporting `HeaderName` with
+  `headerName` and `renderHeaderName`. See the `headers` retype under Changed.
+
+- `baikai`: `Baikai.Error.ErrorCategory` gains `ContentFiltered` (wire tag
+  `content_filtered`, never retryable) with the smart constructor
+  `contentFiltered`. OpenAI's `finish_reason: "content_filter"` and Anthropic's
+  `refusal` stop now carry it. Both used to be `OtherError`, so the only way to
+  tell a filtered response from any other non-retryable failure was to match on
+  the message text. __Breaking__ for a consumer whose `case` over
+  `ErrorCategory` is exhaustive without a wildcard. (REV-1 1.7 residual.)
+
+- `baikai` (breaking to construct, not to read): every record that can still
+  grow a field is now built from an exported base value and refined by record
+  update, and its constructor is no longer exported —
+  `Baikai.Provider.Registry.ApiProvider` (`apiProvider` /`apiProviderWith`),
+  `Baikai.Evidence.ModelCallEvidence` (`baseEvidence`),
+  `Baikai.Evidence.EvidenceRequest` (`evidenceRequest`), `Baikai.Tool.Tool`
+  (`mkTool`, with `emptyTool` kept for fixtures),
+  `Baikai.Embedding.EmbeddingModel` (`emptyEmbeddingModel`),
+  `Baikai.Cost.Log.CallLogConfig` (`callLogConfig`),
+  `baikai-trace-otel`'s `OtelSinkOptions` (`defaultOtelSinkOptions`), and
+  `baikai-agent`'s `AgentCliOptions` (`agentCliOptions`), `AgentCliRun`
+  (`agentCliRun`), `AgentJob` (`agentJob`) and `AgentConfigPaths`
+  (`emptyAgentConfigPaths`). Selectors, record update, `OverloadedRecordDot`
+  reads and generic-lens labels all keep working; only construction from the
+  constructor stops. Adding `describeThinking` to `ApiProvider` in 0.5.0.0 broke
+  every third-party registration site, and `strengthCeiling` would have broken
+  them again; from this release such an addition is a minor bump. (REV-2 G.1.)
+
+- `baikai`: `Baikai.Provider.apiProvider`, which builds an `ApiProvider` from an
+  `Api` tag and a streaming producer, deriving `complete` with
+  `streamingComplete`; and `Baikai.Provider.Registry.apiProviderWith`, which
+  takes the completer explicitly. Both default `describeThinking` to
+  "nothing requested, nothing translated" and `strengthCeiling` to
+  `EvidenceRequestedOnly`, matching `declaredStrength (Custom _)`.
+
+- `baikai`: `Baikai.Tool.mkTool` — a tool from its name, description and JSON
+  Schema. A tool built from `emptyTool` and sent unchanged reaches the wire with
+  `input_schema: null`; `mkTool` has no such shape.
+
+- `baikai`: `Baikai.Agent.AgentOutputFormat` (`TextFormat`, `JsonFormat`) with
+  `renderAgentOutputFormat` and `parseAgentOutputFormat`, and
+  `AgentRunRequest.outputFormat`, defaulting to `TextFormat`. `baikai-claude`
+  renders `--output-format json` and `baikai-openai` renders `--json`, both
+  right after the effort flags; `baikai-agent` reads it from
+  `jobs.<name>.output-format`. This is the one setting an evidence record needs
+  in order to observe a run's session, model and usage, and asking for it used
+  to require the `provider-args` channel that an operator ceiling closes by
+  default — an operator should not have to open a privileged channel to get a
+  record. (REV-2 F.14.)
+
+- `baikai`: `Baikai.Agent.AgentCeiling` gains three fields and the module gains
+  the vocabulary they need. `allowedTools :: [Text]` names tool grants the
+  operator permits beyond the ones `toolGrantsImpliedBy` (also new) says a
+  capability implies on its own; `maxTimeout :: Maybe NominalDiffTime` and
+  `maxOutputLimit :: Maybe Int` bound what any job may request, the second
+  defaulting to the new `defaultMaxOutputLimit` (67108864, sixty-four
+  mebibytes). `Baikai.Agent.ceilingViolations` is `applyAgentCeiling`'s violation
+  list on its own, so a caller can concatenate it with violations of its own.
+  (REV-2 F.3.)
+
+- `baikai`: `Baikai.Content.toolArgumentsFromText` and
+  `Baikai.Content.isCutOffToolCall`. The first is the single rule that turns a
+  tool call's accumulated argument text into its `arguments` value — empty text
+  is an empty object, non-empty text that does not decode is kept verbatim as a
+  `String` — and both provider assemblers and core's stream-recovery path now
+  use it, so the second means the same thing at every layer.
+
+- `baikai`: new exposed module `Baikai.Provider.Internal.StreamWorker` — the
+  bounded hand-off both HTTP providers now use between their SSE worker thread
+  and the consumer draining the stream. `FrameQueue` is a 64-slot `TBQueue` plus
+  a closed flag; `forkFrameWorker` closes the queue however the body ends, and
+  `withFrameWorker` runs the consumer under `Stream.bracketIO` so the worker is
+  killed when the stream stops. The module is exposed like
+  `Baikai.Provider.Cli.Internal`, outside the PVP promise. See
+  [docs/adr/0010](docs/adr/0010-a-stream-consumer-that-stops-owns-cancelling-the-producer.md).
+
+- `baikai`: every Anthropic model in the generated catalog now carries an
+  explicit `CompatAnthropicMessages` record stating the two request-shaping
+  facts of its generation: `AnthropicMessagesCompat.thinkingStyle` (which
+  extended-thinking wire shape it accepts) and the new
+  `AnthropicMessagesCompat.supportsSamplingParameters` (whether it accepts
+  `temperature`, `top_p` and `top_k`). Both are sourced from
+  `baikai/data/models/anthropic.json`, which the fetcher writes from its
+  curated `anthropicInclude` table, and `baikai-gen-models` now refuses an
+  `anthropic-messages` entry that reaches it without a `compat` block rather
+  than falling back to host auto-detection, which cannot know a generation.
+  This is what fixes `claude-sonnet-5`, whose thinking requests were shaped by
+  a prefix table that did not know the id. See
+  [docs/adr/0009](docs/adr/0009-provider-capability-facts-live-in-the-generated-catalog-record.md).
+
+- `baikai`: two new `Baikai.Evidence.ThinkingAdjustment` constructors,
+  `SamplingDroppedUnsupportedModel` and `SamplingDroppedUnsupportedApi`, encoding as
+  `{"kind":"sampling_dropped_unsupported_model","fields":["temperature","top_p"]}` and
+  `{"kind":"sampling_dropped_unsupported_api","fields":["seed"]}`. They record sampling
+  parameters removed because the model generation rejects them, or because the API has no
+  such field on any generation. Both carry a `fields` array and no `requested` level, so
+  they can appear on a call whose thinking mode is `absent`.
+
+- `baikai`: `Baikai.Evidence.weakensThinking`, which says whether an adjustment weakens the
+  thinking the caller asked for. Strict evidence mode filters through it, so a dropped
+  sampling parameter is recorded without refusing the call — the documented contract is
+  refusing a call that would weaken the requested *thinking level*.
+
+- `baikai`: new exposed module `Baikai.Url` — the one place baikai turns a URL
+  into a host name. `parseUrl` yields a `UrlParts` record with the scheme, host,
+  port and path, plus flags saying whether userinfo, a query string or a
+  fragment were present; it never holds their text, so the value cannot carry a
+  secret into a log line. Alongside it: `urlHost`, `hostMatchesSuffix` (moved
+  from `Baikai.Compat`, which now re-exports both), `renderEndpoint`,
+  `stripApiVersion`, and `baseUrlProblem`, which says why a URL is unusable as a
+  `Model.baseUrl` and what to do instead. See
+  [docs/adr/0008](docs/adr/0008-one-url-host-parser-and-every-consumer-uses-it.md).
+
+- `baikai`: new exposed module `Baikai.Provider.Transport.Classify` — the one
+  rule every HTTP provider uses to classify a transport failure, exporting
+  `classifyTransportException` plus the per-type functions it composes. The rule
+  is *where* the failure happened, not what type it is: anything that breaks or
+  ends the connection after the request went out is `TransientError`, anything
+  that says the request or the configuration is wrong is not retryable, and a
+  programming error stays `OtherError`. It understands all three shapes
+  `http-client` can deliver — an `HttpException` of any constructor, a raw socket
+  `IOException`, and a raw or wrapped `TLSException` — because the manager wraps
+  the connect phase but not the body reader. Core gains direct `build-depends` on
+  `http-types` and `tls`, both already in its install plan. Written for
+  third-party `Custom` providers built on `http-client` as much as for baikai's
+  own two. See
+  [docs/adr/0011](docs/adr/0011-core-owns-transport-failure-classification.md).
+
+- `baikai`: `Baikai.Error.parseHttpDate` and `Baikai.Error.retryAfterSecondsAt`.
+  The first parses an HTTP-date in the IMF-fixdate form servers must send plus
+  the two obsolete forms a recipient must accept; the second converts a
+  `Retry-After` header in either of its forms to seconds against a reference
+  instant, clamping a date already in the past to `0`.
+  `parseRetryAfterSeconds` keeps its integer-only contract, now a deliberate
+  division of labour rather than a limitation.
+
+- `baikai`: new exposed module `Baikai.Http` — `canonicalBaseUrl`,
+  `getClientEnvCached` and `cachedClientEnvCount`, the process-global
+  `ClientEnv` cache that both HTTP provider packages now share instead of each
+  keeping its own. Core gains direct `build-depends` on `servant-client`,
+  `http-client` and `http-client-tls`, which were already in its install plan
+  through the `openai` SDK.
+
+- `baikai`: `Baikai.Evidence.ThinkingModeNotTranslated`, encoded as
+  `"not_translated"`, and `Baikai.Evidence.untranslatedThinking`; and
+  `Baikai.Evidence.Build.requestedTranslation`. A path where no adapter ran to
+  translate the caller's level now records the level and says the translation is
+  unknown, instead of saying nothing was asked. (REV-2 D.2.)
+
+- `baikai`: `Baikai.Evidence.Build.missingEvidenceError`,
+  `Baikai.Evidence.Build.strictnessOf` (moved here from `Baikai.Trace`, where it
+  was private), `Baikai.Stream.requireEvidenceOnTerminal` and
+  `Baikai.Provider.Registry.requireEvidenceOnResponse`. (REV-2 D.3.)
+
+- `baikai`: `Baikai.Evidence.usageEnvelope`, and
+  `Baikai.Evidence.Build.endpointIdentityAt`, `prepareEvidenceAt` and
+  `minimalEvidenceAt`, which take the base URL the adapter actually resolved.
+  The three unsuffixed functions remain and pass the model's own field.
+  (REV-2 D.8, D.11.)
+
+- `baikai`: `Baikai.Evidence.deriveStrength`, the single rule that turns an
+  observed model, a provider request id and a response id into an
+  `EvidenceStrength`. (REV-2 D.10.)
+
+### Changed
+
+- `baikai`: catalog refresh. `claude-opus-5` joins the curated Anthropic include
+  set (adaptive thinking, sampling parameters rejected — the facts
+  `docs/plans/60-make-anthropic-thinking-style-and-sampling-support-catalog-driven.md`
+  said whoever curated it in would have to state), and the `gpt-5.6` family
+  picks up its price cut: `gpt-5.6` and `gpt-5.6-sol` to $4.00/$20.00,
+  `gpt-5.6-terra` to $2.00/$12.00, `gpt-5.6-luna` to $0.20/$1.20 per Mtok, cache
+  rates in step. `Baikai.Models.Generated` gains `anthropic_claude_opus_5` and
+  now carries 36 enabled models. No OpenAI id was added: the `gpt-5.6` family is
+  still the newest one models.dev reports that speaks
+  `openai-chat-completions`.
+
+- `baikai` (breaking): `ResponseFormat`'s `JsonSchema` carries a
+  `JsonSchemaFormat` record — `name`, `schema`, `strict`, exported
+  selector-only with the base `jsonSchemaFormat name schema` — instead of
+  holding the three fields directly. As fields of a sum they were partial
+  selectors: `name f` on a `JsonObject` crashed at runtime rather than failing to
+  typecheck, which contradicted the module's own documentation.
+  `-Wno-partial-fields` is dropped from the module. The JSON encoding is
+  deliberately unchanged (`{"tag":"JsonSchema","name":…,"schema":…,"strict":…}`)
+  and is now pinned by a test, because `Options` derives `ToJSON` through it and
+  at least one consumer keys a cache on the result. (REV-2 G.2.)
+
+- `baikai`: `Baikai.Context.appendToolResult` returns its input context
+  unchanged, and runs no dispatcher, when the response is error-shaped. A failed
+  call has no assistant turn worth replaying and no tool calls to answer;
+  appending its empty message put a turn into the transcript the model never
+  took. `runToolLoop` has always stopped on such a response — the documented
+  direct round trip in `docs/user/tools.md` reaches `appendToolResult` instead,
+  and now behaves the same way. Its Haddock also stops claiming multi-call
+  concurrency lives in the dispatcher: the calls are traversed in order.
+  (REV-2 G.7.)
+
+- Release metadata (REV-2 G.8): every publishable package now declares
+  `tested-with: GHC ==9.12.4` and ships its `CHANGELOG.md` (a symlink to the
+  root one, as `baikai` already did) via `extra-doc-files`, so Hackage shows a
+  changelog and a tested compiler for all seven. `baikai-claude` and
+  `baikai-openai` describe what they actually contain — four surfaces each, not
+  "wraps package X" — and `baikai-trace-otel`'s `streamly-core` bound is
+  `>=0.3 && <0.5`, matching every other package in the workspace rather than
+  excluding the 0.4 series the others accept.
+
+- `baikai` (breaking): `Options.headers` and `Model.headers` are keyed on
+  `Baikai.Header.HeaderName` — a newtype over a case-insensitive `CI Text` that
+  keeps the original spelling — instead of `Text`. A header name is
+  case-insensitive on the wire, so a `Map Text Text` holding both
+  `Authorization` and `authorization` sent whichever the assembling fold reached
+  last; the map now holds one entry per header and the last write wins, as a
+  caller writing two spellings would expect. `HeaderName` has an `IsString`
+  instance, so `Map.singleton "x-test" "1"` and `#headers` updates keep
+  compiling; the spelling given is what goes out on the wire and into JSON.
+  (REV-2 G.5.)
+
+- `baikai` (breaking): `Options.stopSequences` is `[Text]`, where empty means
+  "send nothing", instead of `Maybe (Vector Text)` — `Nothing` and `Just []`
+  were indistinguishable on the wire and only one of them could be right. Plan
+  43's rule is lists for caller-side configuration and `Vector` for
+  provider-bound sequences; this was the one field breaking it. `Options.seed`
+  is `Maybe Int` rather than `Maybe Integer`: a seed is a machine integer at
+  every provider that accepts one, and it now sits beside
+  `timeoutMs :: Maybe Int`. (REV-2 G.5, R14.)
+
+- `baikai` (breaking): `StopReason.Aborted` is removed. Nothing produced it —
+  timeouts are `ErrorReason`/`TransientError`, and a consumer abort is recorded
+  as evidence `CallAborted` — while `responseError`, `eventsFor` and
+  `runToolLoop` all treated it as a *success*, so a value that reached any of
+  them would have been silently mishandled. Since 0.6.0.0 a stream consumer that
+  stops cancels the producer, so no consumer is left to receive such a terminal
+  either. (REV-2 B.6.)
+
+- `baikai`: dispatching a model whose `api` is still `emptyModel`'s
+  `Custom ""` says so — `No provider registered for API: <blank Custom tag —
+  emptyModel.api was never set>` — where the message used to end after the
+  colon. `emptyModel`'s Haddock says the same thing. (REV-2 G.4.)
+
+- `baikai`: `withTrace` and `withTraceStream` wait at most one second for the
+  trace sink after writing the shutdown sentinel. On expiry the worker is
+  abandoned — not killed, which would abort the sink's fold mid-step and lose
+  its end-of-stream action — the call proceeds, and one stderr line reports
+  `the trace sink did not confirm delivery within 1000 ms; its worker was
+  abandoned, and events already queued may still be delivered later`. A sink
+  that blocked forever used to hold the call forever and swallow the first
+  attempt to cancel it. A caller under `EvidenceRequired` whose sink did not
+  confirm delivery gets a failed call, through the same path a throwing sink
+  takes; `Baikai.Evidence.Build.sinkFailureError` now says "its record was not
+  confirmed written" rather than "not written", which is the honest claim for
+  an abandoned worker whose events are still queued. The synthetic terminal a
+  consumer's abort produces is delivered from a garbage-collection hook and is
+  not guaranteed before process exit; that was always true and is now stated in
+  `docs/user/model-call-evidence.md`, `docs/capabilities/call-tracing.md` and
+  the `Baikai.Trace` module documentation, with the pattern for callers who need
+  the record. See
+  [docs/adr/0015](docs/adr/0015-trace-cleanup-is-bounded-and-abort-cleanup-is-gc-eventual.md).
+  (REV-2 D.5, Theme 7.3.)
+
+- `baikai`: `Baikai.Trace.Sink.multiSink` runs each member on its own drain
+  thread behind its own unbounded channel, instead of folding `Fold.tee` across
+  the list. `Fold.tee` runs one member then the other and lets either's
+  exception escape, so a single throwing member stopped delivery to every
+  sibling for the rest of the call and skipped their end-of-stream actions — an
+  OpenTelemetry span paired with an unwritable file sink was opened and never
+  ended, and nothing was exported. The step never blocks; the final action sends
+  every member the sentinel, waits for every member, and reports one aggregate
+  failure naming each failed member by zero-based index
+  (`1 of 2 member sinks failed: member 0: …`). (REV-2 D.6.)
+
+- `baikai`: `AgentSafety.allowedTools` is documented as the __grant__ it is.
+  On Claude Code it renders `--allowedTools`, whose help reads "list of tool
+  names to allow": it pre-approves tools the permission mode would otherwise
+  raise a request for, and in an unattended run a request nobody answers is
+  denied. The old Haddock called it "optional narrowing of the provider's tool
+  set", which was the opposite, and `applyAgentCeiling` never looked at it. It
+  is now bounded: a grant passes when the maximum capability implies it
+  (`read-only` implies `Read`, `Glob`, `Grep`, `NotebookRead`, `TodoWrite`;
+  `edit-workspace` adds `Edit`, `MultiEdit`, `Write`, `NotebookEdit`;
+  `full-access` implies every grant) or when the operator named it in
+  `policy.allowed-tools`. Matching is exact, so `Bash(git *)` is not `Bash`.
+  A repository job that grants itself `Bash` under `edit-workspace` — which
+  passed unexamined before — is now refused with exit 77 before any process is
+  created. (REV-2 F.3.)
+
+- `baikai` (breaking): `Baikai.Agent.CeilingViolation` gains five constructors:
+  `ToolGrantForbidden`, `TimeoutExceeded`, `OutputLimitExceeded`,
+  `RepositoryScopeForbidden` and `WorkingDirOutsideRepository`. A `case` over
+  the type that was exhaustive is no longer.
+
+- `baikai` (behaviour): the default ceiling has a finite `maxOutputLimit`, so
+  `applyAgentCeiling defaultAgentCeiling` now refuses a request whose
+  `outputLimit` is `Nothing` — capture without bound is exactly what the
+  maximum exists to refuse. Jobs resolved through `baikai-agent` are unaffected:
+  that layer's own default supplies a finite limit, and only an explicit
+  `output-limit "unlimited"` reaches the ceiling as `Nothing`.
+
+- `baikai`: a tool call cut off by the output cap is no longer executed.
+  `runToolLoop` stops with the response and its tool calls intact when any call
+  is cut off, and `appendToolResult` appends a `ToolResultMessage` with
+  `isError = True` explaining why instead of calling the dispatcher. Previously
+  both assemblers replaced truncated arguments with `{}` and a tool loop
+  happily ran the call with no arguments at all. (REV-2 B.2.)
+
+- `baikai`: `Baikai.Model.anthropicMessagesCompatFor` no longer overlays a
+  thinking style guessed from the model id onto a model whose `compat` is
+  `CompatNone`. `CompatNone` now means host auto-detection alone — the budget
+  thinking shape, sampling parameters supported. Every catalog model carries an
+  explicit record, so this changes nothing for them; a **hand-rolled** model
+  naming an adaptive-era id (`claude-sonnet-5`, `claude-opus-4-7`,
+  `claude-opus-4-8`, `claude-fable-5`) must now carry
+  `CompatAnthropicMessages (defaultAnthropicMessagesCompat {thinkingStyle = AnthropicThinkingAdaptive, supportsSamplingParameters = False})`
+  or start from the catalog value.
+
+- `baikai`: `Baikai.Evidence.evidenceSchemaVersion` is now
+  `baikai.model-call-evidence/1.1`. A minor bump: the two sampling adjustment kinds are a
+  compatible addition, and no previously recorded digest changes.
+
+- `baikai`: HTTP 413 classifies as `ContextOverflow` rather than `OtherError`,
+  from the status alone and whatever the body says. 413 *is* the size-limit
+  status and the caller's remedy — shrink the input — is the same either way;
+  making the category depend on body wording would recreate for 413 the
+  inconsistency this release fixes for connection resets. (REV-2 A.7.)
+
+- `baikai`, `baikai-claude`, `baikai-openai`: an HTTP-date `Retry-After` is
+  converted to seconds instead of ignored. Both transports use the response's own
+  `Date` header as the reference instant, falling back to the local clock, so a
+  CDN-fronted `429` — the common case for a date-valued `Retry-After` — now
+  carries a hint rather than leaving the caller to guess. (REV-2 A.9.)
+
+- `baikai`: **breaking.** `Baikai.Embedding.EmbeddingModel.apiKey` is now
+  `Maybe ApiKeySource` rather than `ApiKeySource`. `Nothing` means the
+  conventional environment variable for the model's host, from
+  `defaultApiKeyEnvForBaseUrl` — the same table the chat providers use — and a
+  host that table does not know refuses with an `AuthError` naming
+  `EmbeddingModel.apiKey`. Migration: `apiKey = source` becomes
+  `apiKey = Just source`. `EmbeddingModel` also derives `Eq` and `Generic`, so
+  the `#field .~ value` idiom works on it as it does on every other record.
+  (REV-2 E.3.)
+
+- `baikai`: **breaking.** `AgentRunFailure`'s `RunTimedOut` constructor now
+  carries a new record `AgentTimedOut` — the configured `limit` plus the
+  `stdout` and `stderr` a timed-out run drained before its process group was
+  killed — instead of a bare `NominalDiffTime`. A caller matching
+  `RunTimedOut limit` becomes `RunTimedOut timedOut` and reads `timedOut ^.
+  #limit`; `renderAgentRunFailure` is unchanged in what it says. The bytes were
+  always there, drained from the moment the child was spawned, and were simply
+  dropped on the timeout path — which is the run an operator most wants an
+  account of, because the tool started, may have consumed tokens, and may
+  already have changed the working tree.
+
+- `baikai`: under `EvidenceRequired`, a successful terminal that carries no
+  evidence record fails the call with `missingEvidenceError` rather than
+  returning a silent success with zero `call_evidence` lines. Strict mode
+  guaranteed that a record which was built and then lost fails the call; it did
+  not guarantee that one was built. The rule is applied at both dispatch points,
+  so `completeRequest` with no sink gets the same guarantee as a streaming call;
+  a failed call keeps the provider's own error, and best effort is unchanged.
+  See `docs/adr/0014-strict-evidence-means-a-record-exists.md`. (REV-2 D.3.)
+
+- `baikai`: a caller's thinking level is recorded on every evidence path — the
+  consumer abort, an unregistered provider, a `complete` handler that threw, and
+  each provider's `immediateError`. The abort path asks the registered adapter's
+  own `describeThinking`; the others record `not_translated`. All four used to
+  record the caller's request as `absent`, which
+  `docs/adr/0002-requested-translated-observed-are-never-collapsed.md` forbids.
+  (REV-2 D.2.)
+
+- **`baikai.model-call-evidence/2.0`.** Two digests cover different bytes, so a
+  verifier must now select its rules by `schema_version`. `response_commitment`
+  covers the provider-reported token counts and never baikai's computed cost:
+  the cost comes from the caller's catalog rates rather than from the response,
+  so the digest used to change whenever a price was edited and a verifier
+  holding only the response could not recompute it. `request_configuration`
+  summarises `output_config` and `response_format` as it already summarised
+  `tools`, because a structured-output JSON schema carries author-written
+  `description` strings and is content wherever it appears — the same schema was
+  stripped from `tools[].input_schema` and survived verbatim through the other
+  two keys. `thinking.mode` may also now be `"not_translated"`, which is a
+  compatible addition. (REV-2 D.7, D.11.)
+
+- **Breaking.** `baikai`: `Baikai.Provider.Registry.ApiProvider` gains a fifth
+  field, `strengthCeiling :: EvidenceStrength`, and
+  `Baikai.Evidence.Build.checkEvidenceRequirements` takes that ceiling where it
+  took an `Api`. The gate compared against `declaredStrength`, a table keyed by
+  the API tag, which necessarily answered `EvidenceRequestedOnly` for every
+  `Custom` transport — so a gateway that genuinely observes a model could never
+  satisfy a strict caller who required that it did. Only a provider knows what
+  its evidence reaches. `EvidenceRequestedOnly` reproduces the old behaviour for
+  any custom provider; the four built-in providers fill the field from
+  `declaredStrength`, which is unchanged in value and still used by the
+  unattended-agent surface. (REV-2 D.10, G.1.)
+
+- `baikai`, `baikai-claude`, `baikai-openai`: one strength derivation replaces
+  three. An observed **response id** now counts as correlation alongside a
+  captured request-id header, so a host that names its model and its response id
+  on every chunk but sends no header reaches `model_observed` instead of
+  `requested_only` — which had put it *below* a host that sent only a header and
+  named nothing. `anthropicStrength` and `openaiStrength` are removed;
+  `Baikai.Provider.Cli.Internal.subprocessStrength` keeps its signature and
+  delegates. (REV-2 D.10.)
+
+### Removed
+
+- `baikai` **0.6.0.0** (breaking): the sixteen `_Type` base-value aliases deprecated in
+  0.3.0.0 — `_Options`, `_Context`, `_Model`, `_ModelCost`, `_Response`,
+  `_Usage`, `_Cost`, `_CostBreakdown`, `_Tool`, `_TextContent`,
+  `_ThinkingContent`, `_ToolCall`, `_ImageContent`, `_EmbeddingModel`,
+  `_InteractiveLaunchRequest` and `_InteractiveLaunchResult`. Each has an
+  `empty…` or `zero…` replacement of the same value, named in the pragma that
+  has been on it since 0.3.0.0. The 0.3.0.0 entry said they remained "for this
+  release"; 0.4.0.0 and 0.5.0.0 shipped without removing them because no entry
+  named a version.
+  `docs/adr/0016-deprecated-names-are-removed-at-the-next-major.md` now fixes
+  the rule: a name deprecated in `A.B.0.0` is removed in `A.(B+1).0.0`, and
+  every pragma says so. (REV-2 G.3.)
+
+- `baikai` **0.6.0.0** (breaking): `Baikai.Trace.newEventId`. It has delegated to
+  `Baikai.Evidence.newCallId` since 0.5.0.0; call that. (REV-2 G.3.)
+
+- `baikai` **0.6.0.0** (breaking): `Baikai.Compat.defaultAnthropicThinkingStyle`, deprecated
+  earlier in this cycle. Nothing in baikai consults it — the thinking style of a
+  first-party Anthropic model is a field of its generated catalog record
+  (`Baikai.Models.Generated`); start from that value, or set
+  `CompatAnthropicMessages` explicitly.
+
+- `baikai` (breaking): `AgentRunRequest.envPassthrough` is renamed `envRequires`.
+  The field is a list of variables the job declares it requires, checked as a
+  precondition; it has never passed anything through, and the KDL key has said
+  `env-requires` since the setting existed.
+
+- `baikai` (breaking): `AgentRunFailure.OutputMalformed`, and with it
+  `baikai-agent`'s exit code 70 and its `internalExitCode` export. Nothing ever
+  constructed the constructor, and giving it a producer would have been wrong:
+  the runner treats the tool's output as best-effort observation and its
+  deliverable is the changed working tree, so a run that edited files correctly
+  and then printed an unparseable final line would have been reported as a
+  failure with its exit code and output discarded. A record's `strength` and
+  `unobserved` fields already say when output could not be read. (REV-2 F.13.)
+
+### Fixed
+
+- `baikai`: the terminal event and its evidence record are pushed to the trace
+  sink exactly once under asynchronous exceptions. The terminal path pushed the
+  evidence record, pushed the terminal event and only then set the
+  already-sent flag; an exception delivered between the last two made the
+  stream finaliser read the flag as unset and push a second `CallEvidence` and
+  an `aborted` `CallFailed` after the real `CallFinished`, so a sink saw two
+  records and two contradictory terminals for one call. All three writes now
+  run inside one `uninterruptibleMask_` with the flag first. (REV-2 D.4.)
+
+- `baikai`: `Baikai.Cost.Log.closeCallLog` is idempotent. The first caller
+  claims the handle and waits for the worker; a second returns at once instead
+  of blocking forever on an `MVar` the worker had already emptied — a shape
+  `withCallLog` makes easy to reach, since its bracket closes a handle the body
+  may also have closed. An `appendEntry` after the close enqueues nothing.
+
+- `baikai`: `reassembleResponse` is total under duplicated, late and
+  timestamp-less input. The first `EventStart` wins the skeleton and
+  `responseId` merges with `<|>`, so a later `Nothing` cannot erase an id an
+  earlier event supplied; events after the first terminal are ignored, so a
+  producer that keeps talking cannot rewrite the answer; and `latencyMs` falls
+  back to the reassembler's own wall clock when neither the skeleton nor the
+  terminal carries a provider timestamp, instead of reporting a zero that reads
+  as "instant". (REV-2 B.7.)
+
+- `baikai`: an `EmbeddingModel` pointed at a non-OpenAI host no longer sends
+  `OPENAI_API_KEY` to it. The default key source was that variable whatever the
+  base URL said, so pointing the client at DeepSeek handed DeepSeek an OpenAI
+  credential. It now resolves per host, and refuses an unknown one. New
+  `resolveEmbeddingKey` and `embeddingClientEnv` expose both decisions without
+  making a request. (REV-2 E.3.)
+
+- `baikai`: `Baikai.Embedding.embed` no longer allocates a TLS manager per call.
+  It used the `openai` SDK's own `getClientEnv`, which builds a fresh manager
+  every time; it now takes one from `Baikai.Http`'s process-global cache, the
+  same one the chat providers use, so an embedding call and a chat call to one
+  host share a connection pool.
+
+- `baikai`: **a credential in a header is no longer printed.** `Options.headers`
+  and `Model.headers` went through derived `Show` and `ToJSON` instances that
+  rendered every value verbatim — while `Baikai.Options`' own documentation
+  invites callers to put a gateway's `Authorization` header there and the
+  getting-started guide tells them to `print resp`, which renders the embedded
+  `Model`. Both types now have hand-written instances that render exactly what
+  the derived ones did, except that the value of a header whose name looks
+  credential-carrying (`authorization`, `api-key`, `apikey`, `token`, `secret`,
+  `cookie`, `password`, or any name ending in `-key`, case-insensitively) prints
+  as `<redacted>`. `Baikai.Auth` exports the three pieces — `redactedMarker`,
+  `isCredentialHeader`, `redactHeaderValues` — so a caller can apply the same
+  rule to its own logging. Only the rendering changes: the field is untouched,
+  `Eq` is untouched, and the header is still sent as written. A JSON round trip
+  of a `Model` is deliberately lossy, since a serialised `Model` is exactly the
+  thing that should not carry a key. (REV-2 E.2.)
+
+- `baikai`: an API-key environment variable set to the empty string, or to
+  nothing but whitespace, now counts as **unset**. `ApiKeyEnv` fails with an
+  `AuthError` naming the variable and saying it is not set or is empty;
+  `ApiKeyEnvChain` skips it and continues, and reports every name when none
+  yields a key. Previously an empty variable resolved to an empty key, which
+  short-circuited a chain and produced `Authorization: Bearer ` and a provider
+  401 that said nothing about the cause. A key with real content is still passed
+  through untrimmed. (REV-2 E.6.)
+
+- `baikai`: **the host parse no longer lets a base URL choose which key baikai
+  sends.** `urlHost` took the text after the *last* `@` anywhere in a URL, so
+  `https://proxy.example.com/v1?u=@api.openai.com` named the host
+  `api.openai.com`: `defaultApiKeyEnvForBaseUrl` resolved `OPENAI_API_KEY`,
+  `autoDetectOpenAICompletions` returned OpenAI's own compatibility record, and
+  the bearer token went to `proxy.example.com`. Anyone who could set `baseUrl` —
+  a `Model` decoded from JSON, a proxy override — could pick which provider's
+  credential to be handed. The same defect broke the benign direction:
+  `https://api.openai.com/v1/@x` named the host `x` and resolved no key at all.
+  The authority now ends at the first `/`, `?` or `#`, and userinfo is only ever
+  the last `@` inside it. (REV-2 A.1 / E.1.)
+
+- `baikai`: `Baikai.Evidence.Build.sanitizeEndpoint` was a second, separately
+  written parser that bounded the authority at the first `/` only, so a URL with
+  a query and no path recorded the wrong host. It is now `renderEndpoint <$>
+  parseUrl`, which also means a recorded endpoint has a lower-cased scheme and
+  host; the path keeps its case and trailing slash.
+
+- `baikai`: `parseCodexJsonlStream` assembles lines in **linear time**. It
+  previously unpacked every chunk into a stream of bytes and appended them one
+  at a time with `BS.snoc`, copying the whole accumulator per byte — quadratic
+  in line length, so one codex event carrying a two-million-character message
+  cost on the order of a trillion byte moves and in practice never finished.
+  Lines are now cut out of each chunk with `BS.elemIndex` and `BS.splitAt`, and
+  the pieces of a line that spans a chunk boundary are joined once. Behaviour is
+  unchanged: a non-JSON line is still skipped, and a last line without a
+  trailing newline is still parsed.
+
+- `baikai`: a Codex custom agent's instructions body renders as a TOML
+  **literal** multi-line string (`'''`), which interprets nothing, instead of a
+  basic one (`"""`), which interprets backslash escapes. As a basic string an
+  instruction as ordinary as "match `\d+`" made Codex refuse to load the file;
+  `tomllib` rejects the old output with `Unescaped '\' in a string`. A body a
+  literal string cannot hold — one containing three apostrophes, a bare carriage
+  return, or a control character other than tab and newline — falls back to a
+  fully escaped basic string. `tomlString`, which renders `name` and
+  `description`, now escapes every control character as TOML 1.0 requires
+  instead of only the five it happened to name.
+
+- Documentation: `baikai`'s Haddock no longer describes behaviour the code left
+  behind. The trace event's token counts are `Maybe` because a non-assistant
+  terminal has no usage, not because the CLI providers report nothing — since
+  0.5.0.0 both carry what the tool reported. `EventStart`'s `partial` is a
+  message skeleton with empty content, zero usage and no stop reason; the api,
+  provider and model id live on the `Response`. A lifted stream's `EventStart`
+  carries the final usage and stop reason already filled in, because the
+  response is complete before the stream begins. `Baikai.CacheRetention` no
+  longer mentions an OpenAI Responses 24-hour bucket no code emits. System
+  prompts are documented as living on `Context.systemPrompt` rather than on a
+  `Baikai.Request` module that no longer exists, `emptyModel`'s `compat` is
+  described as auto-detection rather than a placeholder, tool dispatch says
+  calls run one at a time in order, and every reference to a plan number is
+  gone. (REV-2 H.4.)
+
+## [baikai-claude 0.6.0.0] - 2026-08-28
+
+### Added
+
+- `baikai-claude`: `Baikai.Provider.Claude.Internal.Request` exports `planRequest`,
+  `SamplingPlan`, `uncappedMaxTokensFloor` and `normalizeToolCallId` as test seams.
+  `planThinking` and `describeThinkingFor` are now projections of `planRequest`, so the
+  strict gate, the request builder and the evidence record read one answer.
+
+### Changed
+
+- `baikai-claude`, `baikai-openai` (breaking): each provider's streaming
+  machinery moved from `Baikai.Provider.<P>.Api` to
+  `Baikai.Provider.<P>.Internal.Stream` — the `SseDriver` seam, `liveSseDriver`,
+  `<p>StreamWith`, `Assembler`, `emptyAssembler`, `translate`, and on the OpenAI
+  side `RawChunk`, `RawToolDelta`, `parseChunk`, `parseFrame`, `TagScanState`,
+  `scanThinkTags`, `closeOpenStream`, `RawUsage`, `parseUsage` and
+  `rawUsageToUsage`. `Api` now exports exactly `register`, the provider value
+  and the live stream function. The `.Internal` module is exposed for the test
+  suites and sibling packages and, like every `.Internal` module, may change in
+  any release without a major bump — so changing the assembler stops being a
+  documented break. `Shape`, `Sse` and `Transport` keep their names and gain the
+  same no-guarantees header. `_TagScanState` is renamed `emptyTagScanState`.
+  (REV-2 G.1.)
+
+- `baikai-claude`, `baikai-openai`: a consumer that stops reading now stops the
+  provider. Both packages fork their SSE worker under `Stream.bracketIO` and
+  hand frames through the bounded `FrameQueue` above instead of an unbounded
+  `Chan`. A consumer that cancels — `Ctrl-C`, `System.Timeout.timeout`,
+  `cancel` — releases the HTTP connection immediately; a consumer that abandons
+  the stream (`Stream.take 3`) stops the socket read within 64 further frames
+  and releases the connection at the next major garbage collection. Previously
+  the worker read the entire generation into memory for a consumer that would
+  never look at it, and the provider billed all of it. The three cleanup
+  strengths are stated in
+  [docs/adr/0010](docs/adr/0010-a-stream-consumer-that-stops-owns-cancelling-the-producer.md)
+  and in caller terms in `docs/user/streaming.md`.
+
+- `baikai-claude`: `anthropic_claude_sonnet_4_6` now sends the adaptive
+  thinking shape rather than `budget_tokens`. The budget shape is deprecated
+  for that generation; baikai sends the shape Anthropic documents as current.
+
+- `baikai-claude`, `baikai-openai`: **behaviour change.** `Options.timeoutMs` of
+  `Just n` with `n <= 0` is refused as `InvalidRequest` before the action runs, so
+  no connection is opened. `System.Timeout.timeout` returns immediately at zero
+  and runs unbounded below it, and the previous `max 0` clamp made both spellings
+  fail instantly as a *retryable* `TransientError` — a classification a caller's
+  retry loop re-issues forever for what is a configuration mistake. `Nothing`
+  remains the only spelling of "no bound". (REV-2 A.10.)
+
+- `baikai-claude`, `baikai-openai`: an evidence record's `endpoint` names the
+  host the call actually went to. Both adapters substitute a vendor default for
+  an empty `Model.baseUrl` inside `prepareCall`, so a call with a perfectly
+  definite destination recorded `endpoint: null`. Where no adapter ran, `null`
+  remains the truthful answer. (REV-2 D.8.)
+
+- `baikai-claude`: the `claude` dependency moves from `^>=1.4` to `^>=1.5`.
+  1.5.0 adds a `Pause_Turn` constructor to `Claude.V1.Messages.StopReason`, and
+  `mapStopReason` matches that type with no wildcard under
+  `-Werror=incomplete-patterns`, so the bump forced a decision. A paused turn
+  maps to `Stop`: Anthropic suspends the turn mid-flight for a long-running
+  server-side tool and expects the caller to send the message back to continue
+  it, so nothing failed, and `Baikai.StopReason` has no constructor that says
+  "resume me". Widening that public sum is a breaking change for every consumer
+  who matches on it exhaustively, and it is not this bump's to make. The general
+  rule is
+  [ADR 0018](docs/adr/0018-a-provider-stop-reason-with-no-baikai-equivalent-maps-to-the-nearest-truthful-one.md):
+  a provider stop reason with no baikai equivalent maps to the constructor that
+  is truthful about whether the call failed, and the sum widens only when baikai
+  would behave differently for it.
+
+- `baikai-claude`: `Messages.StreamUsage` lost its `Generic` instance in `claude`
+  1.5.0, so the `message_delta` usage is read through `OverloadedRecordDot`
+  rather than a generic-lens label. `Messages.max_tokens` and
+  `Messages.output_config` became ambiguous selectors — `Messages.Fallback`
+  carries both names — so the provider's tests read them through `^. #max_tokens`
+  and `^. #output_config` instead.
+
+### Removed
+
+- `baikai-claude`, `baikai-openai` **0.6.0.0** (breaking): the eight registration shims —
+  `registerWith`, `registerWithRegistry` and `registerWithRegistryAndConfig` in
+  both `Cli` modules, and `registerWithRegistry` in both `Api` modules. Register
+  the exported provider value instead:
+  `registerApiProvider (claudeCliProvider cfg)`,
+  `registerApiProviderWith reg (codexCliProvider cfg)`,
+  `registerApiProviderWith reg claudeMessagesProvider`. The batch-mode note that
+  had accumulated on `registerWith` — why `complete` stays on the direct path
+  rather than going through `streamingComplete` — moves to the provider value it
+  describes. (REV-2 G.3.)
+
+- `baikai-claude`, `baikai-openai`: `responseToError` and `classifyErrorText`
+  (and its private `classifySdkHttpText` half) from both
+  `.Internal.ErrorClass` modules. Neither package runs a `servant-client` client
+  on the chat path any more, so the `ClientError` branch was unreachable, and the
+  text classifiers parsed a string shape the local SSE transports stopped
+  producing in July. The phrase table `classifyErrorText` held survives as the
+  message fallback inside `classifyErrorFrame`, pinned through the entry point the
+  runtime actually uses. Both modules are documented as outside the PVP-stable
+  surface, so this is not a major bump; version bumps are recorded once, later.
+
+- **Breaking.** `baikai-claude`: `Baikai.Provider.Claude.Api.anthropicStrength`
+  and `baikai-openai`: `Baikai.Provider.OpenAI.Api.openaiStrength`, both replaced
+  by `Baikai.Evidence.deriveStrength`.
+
+### Fixed
+
+- `baikai-claude`, `baikai-openai`: a failure that lands while the response body
+  is streaming is classified as the transient failure it is. A connection reset,
+  a server closing the socket mid-chunk, a body shorter than its declared length
+  and a TLS session torn down after the handshake all now terminate the stream
+  with `TransientError` and `isRetryable = True`, carrying whatever text had
+  already been drained. Every one of them used to be `OtherError` with
+  `isRetryable = False`, while the identical failure at connect time was
+  transient — because `http-client` wraps the connect phase with the manager's
+  exception wrapper and the body reader with nothing that converts a socket
+  `IOException` or a `TLSException`, so those reached the worker raw and missed
+  the `HttpException` branch entirely. (REV-2 A.2.)
+
+- `baikai-claude`, `baikai-openai`: a transport failure mid-stream now closes
+  the blocks that were open when it arrived, on both providers, so a consumer
+  reading raw events and a consumer reassembling them see the same partial
+  output. Both providers built their terminal from the closed blocks alone and
+  silently dropped open text, thinking and tool arguments. On the Claude side
+  this covers `translate (Left …)`, the in-band `error` frame, and the
+  unexpected end of stream. (REV-2 B.3.)
+
+- `baikai-claude`: an SSE frame whose event `type` — or whose
+  `content_block_delta` `delta.type` — the SDK has no constructor for is now
+  skipped instead of ending the stream with a decode error. The SDK decodes both
+  with no unknown-tag fallback, so a new frame type from Anthropic used to be a
+  terminal fault. A frame of a *known* type that still fails to decode remains
+  one. `Baikai.Provider.Claude.Sse` exports the new `decodeFrame`. (REV-2 B.5.)
+
+- `baikai-claude`, `baikai-openai`: an empty `data:` heartbeat is ignored, and
+  on the OpenAI side `[DONE]` is compared after trailing whitespace is trimmed,
+  so `data: [DONE] ` and `data: [DONE]\r` end the stream rather than failing to
+  decode. (REV-2 A.8.)
+
+- `baikai-claude`: every failing stream now begins with `EventStart`. The
+  producer pre-seeds the start event before the first wire read, exactly as the
+  OpenAI producer already did, and `message_start` updates the assembler without
+  emitting a second one. Previously a 401, a rate limit, an in-band `error`
+  frame or an EOF arriving before `message_start` produced a lone `EventError`,
+  breaking the protocol `Baikai.Stream.Event` documents. `StartPayload.responseId`
+  is consequently `Nothing` on both HTTP providers; the provider's message id
+  rides `TerminalPayload.responseId`, which `reassembleResponse` already prefers.
+  (REV-2 A.4, REV-1 Theme 1.1.)
+
+- `baikai-claude`, `baikai-openai`: an asynchronous exception delivered to the
+  stream worker can no longer strand its consumer. End-of-frames is a flag set
+  by the worker fork's own `finally` rather than a sentinel value pushed onto
+  the channel, so a worker that dies without running its normal exit path still
+  ends the stream in an `EventError`. Previously the consumer blocked until the
+  runtime's deadlock detector noticed.
+
+- `baikai-smoke`: two keyed cases against `claude-sonnet-5` — one asking for
+  thinking (which is a 400 before this release) and one setting `temperature` — plus
+  `deepseek-chat` and `openrouter/openai/gpt-4o-mini` in `apiCases`, so the tool and
+  structured-output smokes run against a compatible host that is not OpenAI.
+  `CompatSmoke` now asserts DeepSeek honoured the output cap rather than only that it
+  answered, and `CacheSmoke` asserts the cached token classes cost something.
+
+- `baikai-claude`: a thinking request on `claude-sonnet-5` no longer 400s. It sends
+  `"thinking":{"type":"adaptive"}` and no `budget_tokens`, because the shape is read off
+  the model's catalog record rather than guessed from its id. (REV-2 C.1.)
+
+- `baikai-claude`: `temperature` and `top_p` are no longer sent to a model generation that
+  rejects them with a 400. They are omitted and the omission is recorded as
+  `sampling_dropped_unsupported_model` in the call's evidence. `seed`, `frequencyPenalty`
+  and `presencePenalty`, which the Anthropic Messages API has no field for on any
+  generation, are recorded as `sampling_dropped_unsupported_api`. (REV-2 C.1, C.5.)
+
+- `baikai-claude`: a model whose `maxOutputTokens` is `0` no longer sends
+  `"max_tokens":0`, which Anthropic rejects — and, with thinking set, no longer had its
+  whole thinking plan discarded for not fitting inside a ceiling of zero. It sends
+  `uncappedMaxTokensFloor` (1024, the SDK's own default) instead. An explicit
+  `maxTokens = Just 0` is still forwarded as written. (REV-2 C.2.)
+
+- `baikai-claude`: replay no longer sends an empty text block or an empty `content` array,
+  both of which Anthropic rejects. An empty text block is dropped; an assistant turn left
+  with nothing is dropped whole (it is baikai's own artifact — a block that closed with no
+  deltas, or only unsigned thinking, which replay already omits); a user turn left with
+  nothing is refused locally with a message naming the turn. (REV-2 C.3.)
+
+- `baikai-claude`: tool-call ids that differ only in characters the alphabet forbids, or
+  only past character 64, no longer normalise onto the same id and misroute a tool result.
+  A conforming id passes through unchanged — every id Anthropic and OpenAI actually mint
+  does — and any other is truncated to 51 characters and suffixed with twelve hex
+  characters of its SHA-256. Two `tool_use` blocks in one turn that still collide are
+  refused rather than sent. (REV-2 C.7.)
+
+- Documentation: `baikai-claude`'s and `baikai-openai`'s Haddock point at the
+  functions that exist. `Baikai.Compat` named
+  `Baikai.Provider.OpenAI.Api.mkOpenAIResponseFormat`,
+  `…Api.applyThinkingFormat` and `…Api.translateTextLikeDelta`; the first two
+  moved to `…Internal.Request` and the third is
+  `…Internal.Stream.scanThinkTags`. `ThinkingFormat`'s note said the six
+  non-native shapes all clamp through `compatibleEffort`; three do, Z.ai and
+  Qwen send a bare toggle, and `ThinkingFormatNone` drops the control.
+  `immediateError` carried two `-- |` headers where one was intended.
+  (REV-2 H.4.)
+
+- `baikai-claude`: an Anthropic call reports its thinking tokens. `Usage.reasoningTokens`
+  was hard-coded to `Nothing` on this provider because `claude` 1.4.0's
+  `Messages.Usage` had no breakdown to read; 1.5.0 adds
+  `output_tokens_details.thinking_tokens`, and both `message_start` and
+  `message_delta` now fill the field from it. `reasoningTokens` is an
+  informational subset of `outputTokens`, so no total and no cost moves.
+
+- `baikai-claude`: the prompt-side token counts survive a server-side tool run.
+  The final `message_delta` used to contribute only `output_tokens`, and
+  `inputTokens`, `cacheReadTokens` and `cacheWriteTokens` kept whatever
+  `message_start` had reported — which is wrong for a call whose prompt grew
+  mid-stream. `claude` 1.5.0 exposes those three on `Messages.StreamUsage`, and
+  each is now taken when present. An absent field still keeps the
+  `message_start` figure rather than zeroing it, so a model that sends only
+  `output_tokens` is accounted for exactly as before.
+
+## [baikai-openai 0.6.0.0] - 2026-08-28
+
+### Added
+
+- `baikai-openai`: `Baikai.Provider.OpenAI.Internal.ErrorClass.classifyErrorFrame`
+  and `Baikai.Provider.OpenAI.Api.parseFrame`, which sort a decoded SSE payload
+  into a classified in-band error or a completion chunk.
+
+### Changed
+
+- `baikai-openai`: **breaking.** `Baikai.Provider.OpenAI.Shape`'s
+  `injectThinkingShape`, `describeThinkingShape`, `shapeRequestBody` and
+  `streamRequestBody` take a `Bool` after the compat record — whether the model
+  advertises reasoning support (`Model.reasoning`). A level on a `reasoning = False`
+  model now sends no `reasoning_effort`, `reasoning`, `thinking` or `enable_thinking`
+  key on any host, and records `thinking_dropped_unsupported_model` instead. The model
+  check runs before the host-format check. This is what stops `gpt-4o-mini` plus a
+  level from 400ing. (REV-2 C.4.)
+
+### Fixed
+
+- `baikai-openai`: an in-band `{"error": …}` frame on a `2xx` stream terminates
+  the call with the frame's own classification, status and message. Compatible
+  hosts (OpenRouter, DeepSeek, Together) report an upstream failure they only
+  learned about after committing to a `200` this way, and `parseChunk` never
+  looked at `error`. The pre-fix behaviour was worse than a bad category:
+  OpenRouter's frame carries `choices[0].finish_reason = "error"`, which mapped
+  to `Stop`, so the call ended as `EventDone` with `errorInfo = Nothing` — a
+  consumer switching on the terminal saw a *completed* call. A frame with no
+  `choices` beside the error ended as
+  `OtherError "openai stream ended without finish_reason"`. (REV-2 A.3.)
+
+- `baikai-openai`: reasoning that arrives after visible text closes the open
+  text block before opening the thinking block, so at most one of the two is
+  open at a time, every `_End` precedes the next `_Start`, and no `contentIndex`
+  is revisited after a later one. (REV-2 B.4.)
+
+- `baikai-openai`, `baikai-claude`: **a provider POST no longer follows
+  redirects.** `http-client`'s default is to follow up to ten with every header
+  intact, so a 3xx would have re-sent the bearer token (or `x-api-key`) to
+  whatever host the `Location` header named. `redirectCount` is now zero and the
+  3xx is delivered as the one in-band terminal error carrying its status. Each
+  transport's request builder is exported as `buildRequest`, so the method, the
+  composed path and the redirect policy are assertable without a connection.
+  (REV-2 A.5 / E.4.)
+
+- `baikai-openai`, `baikai-claude`, `baikai`: **the base-URL convention is
+  stated and enforced.** `Model.baseUrl` and `EmbeddingModel.baseUrl` are the
+  API *root* — the host, or the prefix a host mounts the API under — because
+  baikai appends `/v1/chat/completions`, `/v1/messages` or `/v1/embeddings`
+  itself. A trailing `/v1` is accepted and removed rather than doubled, so
+  `https://api.deepseek.com/v1` now requests `/v1/chat/completions` instead of
+  `/v1/v1/chat/completions`. A base URL with no scheme, a scheme other than
+  `http`/`https`, credentials, a query string, a fragment, or a path that is
+  already an endpoint is refused as an `InvalidRequest` naming the problem —
+  and refused *before* a key is read, so an unusable base URL never causes a
+  credential to be looked up. The message renders the URL without its userinfo
+  or query, so it is safe to log. `docs/user/models-and-providers.md` gains a
+  **Base URLs** section stating all of it. (REV-2 A.6.)
+
+- `baikai-openai`, `baikai-claude`: the `ClientEnv` cache was duplicated in each
+  package and keyed on the raw base-URL text, so `https://h` and `https://h/`
+  were two TLS managers and two connection pools to one host. There is now one
+  cache, in `Baikai.Http`, keyed on the canonical rendering of the parsed base
+  URL. `Transport.getClientEnvCached` and `Transport.cachedClientEnvCount` are
+  re-exports of the core functions and keep their signatures.
+
+- `baikai-openai`: the Codex interactive launcher now **refuses the two approval
+  policies the installed CLI rejects**. `codex --help` at `codex-cli 0.149.1`
+  lists exactly `on-request` and `never` for `--ask-for-approval`;
+  `CodexApprovalUntrusted` and `CodexApprovalOnFailure` are older spellings the
+  CLI answers with `error: invalid value 'untrusted' for
+  '--ask-for-approval'`. Rendering them made a launch return `Right` carrying a
+  non-zero exit code — a session that ran and failed — instead of the `Left
+  SafetyNotExpressible` this module promises for a policy that cannot be
+  honoured. They are refused before any process is created, and refused rather
+  than quietly mapped onto `on-request`, because substituting a different
+  approval policy would change what the caller asked for. The constructors and
+  their spellings are unchanged, so code that matches on `CodexApprovalPolicy`
+  keeps compiling.
+
+## [baikai-trace-otel 0.4.0.0] - 2026-08-28
+
+### Added
+
+- `baikai-trace-otel`: `OtelSinkOptions` derives `Generic`, so `#spanName`
+  resolves on it. No `Eq` or `Show`: `OpenTelemetry.Context.Context` has neither,
+  and an instance that ignored `parentContext` would be a lie. (REV-2 G.6.)
+
+- `baikai-trace-otel`: `OtelSinkOptions.parentContext :: Maybe Context`, default
+  `Nothing`. When set, every span the sink opens becomes a child of the span in
+  that context instead of a root, so a call can be nested under the caller's own
+  request span. It is a value fixed when the sink is built rather than an action
+  run per call, because the fold runs on baikai's trace worker thread where the
+  caller's thread-local context is invisible: capture the context on your own
+  thread (`ctx <- getContext`, or `Context.insertSpan mySpan Context.empty`) and
+  build the sink for that request. __Breaking for positional construction__ of
+  `OtelSinkOptions`; the documented path is a record update on
+  `defaultOtelSinkOptions`. (REV-2 D.9.)
+
+### Changed
+
+- `baikai-trace-otel`: the `baikai.evidence.strength` span attribute is rendered
+  by `Baikai.Evidence.renderEvidenceStrength`, the function the JSON encoding
+  uses, instead of a second spelling local to the sink that could drift from it.
+
+- `baikai-trace-otel`: `gen_ai.response.model` is set only by the evidence
+  branch, from the model the provider reported. The terminal branch set it from
+  the *requested* id, and since evidence is pushed before the terminal and
+  `addAttributes` replaces a key, that both labelled a request as an observation
+  on every call without evidence and overwrote the genuinely observed value on
+  every call with one. (REV-2 D.1.)
+
+## [baikai-effectful 0.4.0.0] - 2026-08-28
+
+### Changed
+
+- `baikai-effectful` (breaking): the version is a **major** bump although this
+  package's own exports are unchanged. Its `baikai` bound moves to `^>=0.6.0`,
+  and the `Baikai` effect's three operations are typed in `Model`, `Context`,
+  `Options` and `Response` — every one of which baikai 0.6.0.0 changes
+  breakingly. A consumer therefore meets a break through this package even
+  though nothing in it was renamed, so the number says so rather than making
+  `0.3.0.4` look like a safe upgrade.
+
+- `baikai-effectful`: no longer depends on `streamly`. Both stanzas listed it
+  while every module imports only `Streamly.Data.Fold` and
+  `Streamly.Data.Stream`, which are `streamly-core`. (REV-2 minor.)
+
+## [baikai-kit 0.2.0.0] - 2026-08-28
+
+### Added
+
+- `baikai-kit`: `Baikai.Kit.Error` with the closed `KitError` sum, its
+  `Exception` instance and `renderKitError`; `Baikai.Kit.Path.safeSourcePath`,
+  which resolves an untrusted relative source below the kit checkout and refuses
+  a symbolic link in any component or a canonical path outside the checkout;
+  `Baikai.Kit.Manifest.itemSources`/`ItemSources`, the one pure derivation of an
+  item's source list, and `supportedManifestVersions`;
+  `Baikai.Kit.Sidecar.hashEntries`; `Baikai.Kit.Repo.KitRepo`/`RepoRefresh`;
+  `Baikai.Kit.Install.installFrom`, `renderAvailable` and `UpdateReport`;
+  `Baikai.Kit.Status.StatusReport`, `UpstreamAvailability` and the now-pure
+  `renderStatusTable`; `Baikai.Kit.Command.runKitCommand`. `KitState` gains
+  `KitUpstreamRefused`, rendered `refused`. (REV-2 E.5, F.10, F.11.)
+
+- `baikai-kit`: `Baikai.Kit.Install.OverwritePolicy` (`KeepLocalEdits`,
+  `OverwriteLocalEdits`), `reinstallPresent` (the network-free half of
+  `updateKit`), and `PlannedWrite`/`WriteContent`/`executePlan`/`executePlanWith`
+  as a test seam. `SidecarMeta` gains `installedFiles` and `installedHash`,
+  which record what this tool wrote for one provider and the hash of exactly
+  those bytes; `newSidecarMeta` takes both. `kit update` gains `--force`.
+  (REV-2 F.12, Theme 8.2.)
+
+### Changed
+
+- **Breaking.** `baikai-kit`: every library function returns
+  `Either KitError a` and prints nothing; only
+  `Baikai.Kit.Command.runKit` prints `Error: …` and exits 1. `loadManifest`,
+  `loadManifestMaybe`, `installItem`, `listAvailable`, `uninstallItem`,
+  `updateKit` and `ensureKitRepo` change shape accordingly, `computeKitHash`
+  takes the kit root, a base and relative file names, `kitStatus` returns a
+  `StatusReport` instead of printing, and `KitUpdate`'s report is rendered by
+  the caller. See `docs/adr/0013-library-code-never-calls-exitfailure.md`. A
+  consumer that only calls `runKit` and `kitCommandParser` needs no change; one
+  that calls the library directly binds `Right`. (REV-2 F.11.)
+
+- `baikai-kit`: a kit is plain files. Install, the content hash and `kit status`
+  resolve every listed source through `safeSourcePath`, so a kit repository that
+  commits a symbolic link can no longer have a file read through it and copied
+  into a provider directory. `kit status` shows such an item as `refused`.
+  (REV-2 E.5 = F.10.)
+
+- `baikai-kit`: a manifest whose `version` is not 1 or 2 is refused with
+  `KitManifestVersionUnsupported` instead of being decoded and installed.
+  (REV-2 F.12.)
+
+- `baikai-kit`: an agent that lists several `files` installs all of them. The
+  first becomes the provider's agent file as before, and each remaining file
+  goes into a resource directory named after the agent beside it
+  (`<agents dir>/<name>/<file>`), which uninstall removes with the agent. Only
+  the first file used to be installed. (REV-2 F.12.)
+
+- `baikai-kit`: `kit update` skips an item whose installed files no longer hash
+  to what its sidecar recorded, printing the `--force` invocation that would
+  overwrite them; `kit update --force` reinstalls anyway. Sidecars written
+  before this release carry no such hash and are updated without the check.
+  (REV-2 Theme 8.2.)
+
+### Removed
+
+- **Breaking.** `baikai-kit`: `Baikai.Kit.Path.safeUnder` (exported and unused),
+  `Baikai.Kit.Manifest.agentSources` (replaced by `itemSources`) and
+  `Baikai.Kit.Install.uninstallOutcomes` (absorbed by `uninstallItem`, which now
+  returns the outcomes for the caller to render). The internal `requireSafe` and
+  `Baikai.Kit.Status.resolveCacheOrEmpty` are gone with the exits they wrapped.
+
+### Fixed
+
+- `baikai-kit`: `kit status` with no cache and no network prints
+  `No kit items installed.` and exits 0. It used to exit 1: the guard around
+  `ensureKitRepo` caught `IOException`, which is not what `exitFailure` throws.
+  (REV-2 F.11.)
+
+- `baikai-kit`: `Baikai.Kit.Status.upstreamHash` joined the manifest `path`
+  without validating it, a second unsanitised join that grew after the July
+  hardening pass validated the first. Both now go through `itemSources` and
+  `safeSourcePath`. (REV-2 Theme 8.1.)
+
+- `baikai-kit`: an install that fails while renaming files into place now
+  restores what was there before, or names the paths it could not restore.
+  Phase two was a bare loop of renames, so a failure part-way left earlier
+  renames in place while the message said "no changes were made". Temporary
+  files are also created with `openTempFile`, so two concurrent installs of one
+  item no longer clobber each other's staging file, and a destination that is a
+  directory is refused before anything is written. (REV-2 F.12.)
+
+- `baikai-kit`: `Baikai.Kit.Install.stripYamlFrontmatter` normalises line
+  endings to LF on every branch. Input without frontmatter, and input whose
+  frontmatter is never closed, used to keep their `\r` characters and leak them
+  into the Codex agent TOML. (REV-2 Theme 8.7.)
+
+- `baikai-kit`: an `IOException` raised while reinstalling during `kit update`
+  is returned as `KitWriteFailed` instead of escaping as an uncaught exception.
+  (REV-2 Theme 8.4.)
+
+## [baikai-agent 0.2.0.0] - 2026-08-28
+
+### Added
+
+- `baikai-agent`: three operator-only `policy` keys — `policy.allowed-tools`,
+  `policy.max-timeout` (a duration or `"unlimited"`) and
+  `policy.max-output-limit` (a byte count or `"unlimited"`) — each defaulting
+  from `defaultAgentCeiling`, and all six ceiling fields now printed by
+  `agent show` and carried in its `--json` object.
+
+- `baikai-agent`: `Baikai.Agent.Config.repositoryScopeViolations`, which reads
+  the resolution report to say which values the untrusted repository file was
+  not allowed to supply at all. `Baikai.Agent.Cli` concatenates its answer with
+  the pure ceiling's, so an operator sees one refusal naming every problem.
+
+### Changed
+
+- `baikai-agent` (breaking): `AgentConfigScope`'s constructors are
+  `AgentUserScope` and `AgentRepositoryScope`. `UserScope` collided with
+  `baikai-kit`'s `KitScope` constructor of the same name, the one clash between
+  two baikai-family packages. (REV-2 G.5.)
+
+- `baikai-agent` (breaking): a relative `working-dir` resolves against the
+  repository root rather than the process's own directory, so `working-dir "."`
+  means the checkout whichever file declared it. Resolving against the process
+  directory made `"."` mean two places when two documents defined one job, since
+  which one it was depended on which layer won. An absolute path is unchanged.
+  (REV-2 F.14.)
+
+- `baikai-agent` (breaking): every `--json` output is now built with `aeson`
+  rather than a hand-rolled writer, and `agent show --json` always emits one
+  object with the same seven keys — `job`, `outcome` (`shown`, `refused` or
+  `failed`), `exitCode`, `message`, `configuration`, `ceiling`, `command` —
+  with `null` for the parts that do not apply. Previously a refusal emitted a
+  different shape from a success and a document that would not parse emitted a
+  bare resolution report or nothing at all, so a reader had to know which
+  failure mode it was looking at before it could find the exit code. `run --json`
+  keeps its `outcome` values and `list --json` is unchanged. (REV-2 F.14.)
+
+- `baikai-agent` (breaking): `--run-id` or `--require-evidence` without either
+  `--evidence-file` or `--json` is now a usage error (64) naming both fixes.
+  Before, the record was built — a `--version` probe of the tool and two digests
+  — and then dropped. Under `--json` the record now travels in the envelope as
+  `evidence`, encoded by the same `ToJSON` `--evidence-file` writes.
+
+- `baikai-agent`: `agent show` and `agent run` no longer print another job's
+  unknown-key warnings, or the operator file's `policy` keys. The declaration
+  describes one job and the ceiling is a separate declaration, so `settei` warns
+  about both; neither is a mistake and a document with four jobs printed three
+  jobs' worth of noise on every run. A misspelled key inside the selected job
+  still warns, and a `policy` node in the *repository* document earns exactly one
+  notice saying it has no effect. `Baikai.Agent.Config` exports the two filters,
+  `relevantWarnings` and `repositoryPolicyNotice`. (REV-2 F.13.)
+
+- `baikai-agent`: an evidence record's `endpoint` resolves a relative executable
+  against the job's working directory before probing it, because that is what
+  the child execs. A job whose `executable` is `./bin/agent` previously reported
+  a path resolved against the parent's own directory, which does not exist.
+  `Baikai.Agent.Run` exports `executableForEvidence`. (REV-2 F.13.)
+
+- `baikai-agent`: a failed run's `error_info.message` keeps the last
+  `errorInfoStderrTailBytes` (4096) bytes of standard error, prefixed with how
+  many earlier bytes were dropped, instead of the whole captured stream — which
+  the output limit allows to reach four mebibytes by default. `Baikai.Agent.Run`
+  exports the constant. (REV-2 F.13.)
+
+- `baikai-agent`: `--evidence-file` stages through a uniquely named temporary
+  file created with `O_EXCL` beside the destination, instead of the destination
+  plus `.partial`. A symbolic link planted at the old, guessable name was
+  followed, which let an unattended run overwrite a file of the planter's
+  choosing. (REV-2 F.13.)
+
+- `baikai-agent` (breaking): an operator configuration file that lies inside the
+  repository root is refused with exit 78, naming the file and the root, and no
+  ceiling is established. The source list already refused the repository
+  *document*; this closes the shape where the repository supplies the *operator*
+  document, which both `--user-config .baikai/policy.kdl` and
+  `XDG_CONFIG_HOME=$PWD/.baikai` produce. `--user-config`, `XDG_CONFIG_HOME` and
+  `HOME` remain the operator's own inputs: the ceiling is exactly as trustworthy
+  as the process environment that selects it, and the guide now says so.
+  (REV-2 F.4.)
+
+- `baikai-agent` (breaking): an unrecognised key under the operator file's
+  `policy` node is an error rather than a warning, naming the file and every
+  such key. Everywhere else a forward-compatible file should not stop an older
+  binary; under `policy` a misspelling would silently leave the default ceiling
+  in force, which for the one node whose purpose is limiting authority is
+  indefensible. Two `AgentConfigError` constructors are added,
+  `CeilingFileInsideRepository` and `UnknownPolicySetting`.
+
+- `baikai-agent` (breaking): `AgentConfigPaths` gains `repositoryRoot`, the
+  directory the process runs in. `--config PATH` chooses which file supplies
+  repository-scope settings and does not move the root, because the root is what
+  confines a repository-supplied `working-dir`.
+
+- `baikai-agent` (breaking): a repository configuration file may no longer set
+  `executable` or a non-empty `extra-dirs`, and its `working-dir` must resolve —
+  after following symbolic links — inside the repository root. Each is refused
+  with exit 77 naming the setting, or naming both directories. The operator's
+  own file and `--set` may still set all three. `executable` turns configuration
+  into code execution with the operator's environment and the prompt on standard
+  input; `extra-dirs` inside the root adds nothing the working directory does not
+  already give, so the only ones a checkout would ask for are outside it.
+  (REV-2 F.3.)
+
+### Removed
+
+- `baikai-agent` (breaking): the `BAIKAI_AGENT_EXECUTABLE` environment binding.
+  An environment variable is inherited by every child process and is easy to set
+  by accident, and naming the program to run is the widest widening there is.
+  An operator whose installation is not on `PATH` writes `executable` in their
+  own configuration file or passes `--set`.
+
+### Fixed
+
+- `baikai-agent`: a timed-out run now **escalates to `SIGKILL`**. The runner
+  interrupts the child's whole process group, then terminates it, then kills it,
+  each of the first two stages bounded by the grace period and ended early once
+  the leader has been reaped and no member of the group is left. Previously the
+  last resort was `terminateProcess` followed by an *unbounded* wait, so a
+  coding agent that ignored `SIGTERM` — or a grandchild holding the output pipe
+  — hung the run for as long as it chose to live, with the deadline already
+  past. Polling the group rather than waiting on the leader alone is also what
+  gives a grandchild the same grace the agent gets.
+
+- `baikai-agent`: a timed-out run **reports the output it drained**. `baikai
+  agent run` prints it under the same stream discipline a finished run gets, so
+  `response=$(baikai agent run job)` under `capture` receives the partial answer
+  with `$?` set to 75, and `--json`'s failure envelope carries the same
+  `stdout`, `stdoutTruncated`, `stderr` and `stderrTruncated` fields. A drain
+  interrupted because something outside the process group still held the pipe
+  open keeps its bytes too, reported as truncated.
+
+- `baikai-agent`: the `baikai` command writes its output as **UTF-8 bytes**
+  rather than through the locale encoding. Where an unattended run actually
+  happens — cron, a systemd unit, a container — the environment says `LANG=C`,
+  and on a platform whose locale encoding follows it a single accented character
+  in the agent's answer made the write throw after the run had already finished:
+  exit 1, answer lost. This mirrors what the prompt read and the prompt write
+  have always done.
+
+- `baikai-agent`: the `baikai` executable now links the **threaded runtime**
+  (`ghc-options: -threaded` on the `executable baikai` stanza). Without it a
+  blocking operating-system call — the `waitpid` inside
+  `System.Process.waitForProcess` — stopped every Haskell thread in the
+  installed binary, so a job's configured `timeout` could never fire and a
+  coding agent that wrote more than one pipe buffer deadlocked against the
+  runner's drain threads. Both defects existed only in the shipped executable:
+  the test suite was already compiled `-threaded`, so every runner test passed
+  under a runtime the binary did not have.
+
+  The suite now proves the runtime the binary ships with rather than its own.
+  `baikai-agent/test/BinaryTests.hs` spawns the built executable — cabal builds
+  it first and puts it on the suite's `PATH` through
+  `build-tool-depends: baikai-agent:baikai` — asserts that `baikai +RTS --info`
+  reports `rts_thr`, and runs `baikai agent run` against a stub agent that
+  outlives its deadline, requiring exit 75 within seconds and the whole process
+  group gone. See
+  [docs/adr/0006](docs/adr/0006-a-process-spawning-executable-ships-on-the-threaded-runtime.md).
+
+## [baikai 0.5.0.0] - 2026-08-05
+
+### Added
+
+- `baikai`: new exposed module `Baikai.Agent`, the provider-neutral vocabulary
+  for an **unattended coding-agent run** — a run with no terminal and no human,
+  which owns its own tool loop, may change files inside directories the caller
+  authorized, and returns a process result rather than a `Response`. It defines
+  `AgentRunRequest` (with a required `workingDir`), `AgentRunResult`, the
+  `AgentCapability` profile (`read-only`, `edit-workspace`, `full-access`),
+  `AgentSafety`, the `AgentOutputMode` and `AgentCapturedOutput` output
+  discipline, the `AgentCommand` renderer/runner boundary with an explicit
+  prompt transport, and the `AgentRenderError` / `AgentRunFailure` taxonomies.
+
+- `baikai`: the operator policy ceiling — `AgentCeiling`,
+  `defaultAgentCeiling`, `CeilingViolation`, and the pure `applyAgentCeiling`.
+  It returns a request unchanged when it is within the ceiling and reports
+  every violation when it is not; it never clamps an over-broad request to the
+  permitted value. The default ceiling permits read-only and edit-workspace
+  authority and refuses full access and raw provider arguments.
+
+  `Baikai.Agent` itself is vocabulary and pure policy algebra only: it spawns no
+  process and renders no command-line flags. Those live in the vendor packages
+  and in `baikai-agent`, below. The module is deliberately not re-exported from
+  the umbrella `Baikai` module, because its field accessors share names with
+  `Baikai.Interactive`, so `import Baikai` continues to compile unchanged.
+
+- `baikai`: new exposed module `Baikai.Evidence`, the vocabulary for
+  **verifiable model-call evidence** — a record of what actually crossed the
+  boundary to a provider, as opposed to what the process was configured to ask
+  for. It defines `ModelCallEvidence` and the `evidenceSchemaVersion` string
+  consumers pin against, `Observed` (a deliberate non-`Maybe` for a value the
+  provider either did or did not report, with no function that supplies a
+  default), `ThinkingTranslation` with its `ThinkingMode` and
+  `ThinkingAdjustment` enumerations describing what a requested
+  reasoning-effort level actually became on the wire and every clamp, collapse,
+  or drop applied on the way, `EndpointIdentity` and `TransportKind`,
+  `CallStatus`, and the ascending `EvidenceStrength` scale.
+
+  It also provides the canonical hashing core: `canonicalEncode` gives a JSON
+  value exactly one byte representation (object keys sorted, no insignificant
+  whitespace, numbers normalised so `1`, `1.0`, `1.00`, and `1e0` all encode as
+  `1`, and a hand-written string escaper so an aeson upgrade cannot silently
+  invalidate a recorded digest); `commitmentDigest` hashes a full request
+  envelope, and `configurationDigest` hashes an allow-list projection
+  (`configurationProjection`) that keeps configuration and replaces content with
+  structural summaries, so two calls that ask the same model the same way about
+  different subjects agree. The two digests are separate on purpose: the first
+  binds a record to a particular request, the second is safe to compare across
+  runs that legitimately differ in content.
+
+  Nothing constructs a `ModelCallEvidence` from a real call yet, and no existing
+  behaviour changed. New dependencies: `cryptohash-sha256` and
+  `base16-bytestring`, both single-purpose packages chosen over a full
+  cryptographic framework.
+
+- `baikai`: `Options` gains an `evidence` field carrying an optional
+  `EvidenceRequest` — the caller's run identifier, retry provenance, and how
+  strictly they need evidence. A call whose `evidence` is `Nothing`, which is
+  every call that does not opt in, behaves exactly as it did before: no digest
+  is computed and no evidence is emitted.
+
+- (Entry added 2026-08-27; the behaviour shipped in 0.5.0.0.) `baikai`: **strict
+  evidence mode**. `EvidenceStrictness` is `EvidenceBestEffort` or
+  `EvidenceRequired !EvidenceStrength`, and a caller who asks for the second
+  gets a call that **refuses to start** — before any request is built or any
+  connection opened — when the configuration cannot reach the strength asked
+  for: `Baikai.Evidence.Build.checkEvidenceRequirements` compares the
+  requirement against what the provider can deliver and against the thinking
+  translation, and `completeRequest` / `streamRequest` return an error-shaped
+  response or a terminal `EventError` instead of dispatching. The gate is
+  pre-dispatch by design; that is the only point at which refusing is still
+  free.
+
+- (Entry added 2026-08-27; the behaviour shipped in 0.5.0.0.) `baikai`:
+  **sink-failure semantics under strict mode**. `Baikai.Evidence.Build`
+  exports `onSinkFailure`, `sinkFailureIsFatal` and `sinkFailureError`: a trace
+  sink that throws fails an `EvidenceRequired` caller's call, because a record
+  the sink did not confirm written is not a record, while a best-effort caller's
+  call succeeds with the failure reported on stderr.
+
+- (Entry added 2026-08-27; the behaviour shipped in 0.5.0.0.) **Breaking.**
+  `baikai`: `Baikai.Provider.Registry.ApiProvider` gained a fourth field,
+  `describeThinking :: Model -> Options -> ThinkingTranslation`, which the
+  pre-dispatch strictness gate calls to learn what a provider would do with the
+  caller's reasoning-effort request without sending anything. Every third-party
+  provider constructed with the `ApiProvider` constructor stopped compiling.
+  This was not recorded at the time; it is the defect that made 0.6.0.0 hide the
+  constructor behind `apiProvider` so that the next field addition is a minor
+  release.
+
+- `baikai`: model-call evidence is now **produced and emitted**. A caller who
+  sets `Options.evidence` gets exactly one `call_evidence` line per call from
+  their trace sink, under every way a call can end: success, provider failure, a
+  consumer that abandons the stream (status `aborted`, not `failed` — an abort
+  is the consumer's doing and reporting it as a provider failure would
+  misattribute it), and dispatch that found no registered handler.
+
+  New exposed module `Baikai.Evidence.Build` bridges the vocabulary to the
+  `Model` and `Options` records: `minimalEvidence` and `prepareEvidence` build a
+  record, `dispatchEnvelope` supplies the request envelope for the paths where
+  no adapter ran, `sanitizeEndpoint` reduces a base URL to scheme/host/port/path
+  with the query string and any userinfo dropped wholesale, and `onSinkFailure`
+  is the hook a future release replaces to make a strict caller's call fail when
+  the trace sink does.
+
+  Every record this release produces has `strength` `requested_only` and every
+  provider-observed field set to `"unobserved"`. That is not a placeholder: it
+  is a truthful record for a transport that has not yet been taught to observe
+  anything. Later releases teach each transport to observe more.
+
+  (Correction added 2026-08-27: the two paragraphs above describe the release
+  inaccurately and are kept as shipped rather than rewritten. `onSinkFailure`
+  did not await a future release — it shipped in 0.5.0.0 together with
+  `sinkFailureIsFatal` and `sinkFailureError`, which already fail a strict
+  caller's call when the sink throws. And not every 0.5.0.0 record has `strength`
+  `requested_only`: the provider entries below describe what each transport
+  reports, and the HTTP adapters reach `correlated` and `model_observed`.)
+
+  **A caller who does not opt in pays nothing.** With `Options.evidence` absent
+  no digest is computed, no call identifier is generated, no evidence event is
+  emitted, and the request envelope is never even forced — the gate lives inside
+  the shared builder rather than at each adapter's call site, and the envelope
+  parameter is deliberately lazy. Both facts are guarded by tests.
+
+- `baikai`: `TraceEvent` gains a `CallEvidence` constructor, encoded as
+  `{"kind":"call_evidence", …}`. A consumer whose pattern match over `TraceEvent`
+  is exhaustive must add a branch; one with a wildcard is unaffected. Filter for
+  it with `jq 'select(.kind == "call_evidence") | .evidence'`. Note that a trace
+  line carries its fields alongside the `kind` discriminator rather than nested
+  under a `data` key, and that the evidence record inside spells its own fields
+  in snake_case — the two encodings differ deliberately, because an evidence
+  record must render an absent field as explicit `null` while a trace line drops
+  it to stay small.
+
+- `baikai`: `Baikai.Provider.Cli.Internal` — the module the two subprocess
+  providers share — gains the vocabulary for reading what a coding-agent CLI
+  reported about its own run. `CodexRunReport` and the new
+  `parseCodexJsonlStream :: Stream IO ByteString -> IO CodexRunReport` fold the
+  `codex exec --json` event stream into its assistant text, its thread
+  identifier, and its token counts, instead of concatenating agent-message text
+  and discarding everything else. `ClaudeCliReport` and
+  `decodeClaudeCliResult` do the same for `claude -p --output-format json`.
+  Every field but the message text is optional, because both tools' event
+  schemas have changed across versions and an absent field is a genuine absence
+  rather than a parse failure. **Breaking** for anyone calling
+  `parseCodexJsonlStream` directly: its result type is no longer `Text`. This is
+  an internal module and is documented as outside the PVP guarantee.
+
+- `baikai`: `Baikai.Provider.Cli.Internal` also gains `ExecutableIdentity` and
+  `executableIdentity`, which resolve a configured executable name to an
+  absolute path and read the tool's own `--version` line. The probe is cached
+  per resolved name for the lifetime of the process, because spawning it per
+  model call would roughly double the process cost of the cheapest possible
+  call, and it is bounded by a five-second timeout so a tool that hangs on
+  `--version` cannot wedge a model call. (Corrected 2026-08-27: the entry said
+  two seconds; `versionProbeMicros` has always been five.) A probe that fails records the version
+  as absent rather than failing the call. It is only ever called from inside
+  the evidence branch: a caller who asked for no evidence must not pay for a
+  process whose only purpose is to describe a tool they were about to run
+  anyway.
+
+- `baikai`: `subprocessStrength` and `cliResponseEnvelope`, also in
+  `Baikai.Provider.Cli.Internal`. The former derives a subprocess call's
+  evidence strength from what the tool reported and **nothing else** — the exit
+  status is deliberately not one of its arguments. The latter spells the
+  response-commitment envelope with the same three keys, in the same shapes, as
+  the two API transports build by hand, so a verifier holding a response can
+  recompute the digest without first knowing which transport served it.
+
+- `baikai`: `Baikai.Agent` gains `AgentRunOutcome` and `agentRunOutcome`. It
+  pairs what an unattended run did — the existing
+  `Either AgentRunFailure AgentRunResult` — with the evidence the runner built
+  for it. The evidence is a sibling of the outcome rather than a field on
+  `AgentRunResult` because the run that most needs a record is one that did not
+  produce a result: a run killed by its own timeout reports
+  `Left (RunTimedOut …)`, so a record hanging off the `Right` would be
+  unreachable exactly there.
+
+### Fixed
+
+- `baikai`: a `call_evidence` event is now emitted **before** its call's
+  terminal `call_finished` or `call_failed`, rather than after. The
+  OpenTelemetry sink ends and removes a call's span on the terminal, so under
+  the old order its evidence-attribute branch was unreachable from any real
+  call and every backend saw a span with no evidence on it — nothing failed,
+  the attributes were simply never there. No consumer can have depended on the
+  old order, because no consumer has ever seen a `call_evidence` line.
+
+- `baikai`: the `ThinkingFormatOpenAI` Haddock in `Baikai.Compat` listed the
+  native `reasoning_effort` vocabulary as `minimal | low | medium | high`, which
+  predates `xhigh` and `max`. It now lists all six and states that this shape
+  alone sends the canonical baikai level verbatim while the other six clamp
+  through `compatibleEffort`. No behaviour changed: the native path's exclusion
+  from that clamp is deliberate and is guarded by two named tests in
+  `baikai-openai/test/ShapeSpec.hs`. A reader who consulted the comment to
+  decide whether `xhigh` was safe to use against OpenAI has until now been told
+  something untrue.
+
+### Changed
+
+- **Breaking:** `baikai`: `TerminalPayload` gains an `evidence` field and the two
+  terminal smart constructors take it as their new first argument:
+  `doneTerminal :: Maybe ModelCallEvidence -> Maybe Text -> StopReason -> Message -> TerminalPayload`
+  and `errorTerminal` likewise. `Response` gains the same field. A custom
+  provider implementation must pass `Nothing` (or a record it builds through
+  `Baikai.Evidence.Build`); a custom `Response` built with the record
+  constructor must add `evidence = Nothing`. Code that only pattern-matches on
+  these types is unaffected.
+
+- **Breaking:** `baikai`: `CallFinished` gains `cachedInputTokens`,
+  `cacheWriteTokens`, `reasoningTokens`, and `totalTokens`. The trace path used
+  to drop counts that `Baikai.Cost.Log.CallLogEntry` kept from the same `Usage`
+  value, which made the cost log strictly more faithful than the trace.
+
+- **Breaking:** `baikai`: a computed cost of **zero is now reported as zero**
+  rather than suppressed, in `CallFinished` and at all three `CallLogEntry`
+  construction sites. Previously `usd` was omitted whenever the cost came out at
+  zero, so "this call was free" and "baikai could not price this call" were
+  indistinguishable — and the subscription-based CLI providers always price at
+  zero, so that was the common case rather than a corner. **A cost dashboard
+  that treated an absent `usd` as "unpriced" will now count those calls as
+  costing zero.** That is the correct reading, but it changes what such a
+  dashboard shows.
+
+- **Breaking:** `baikai`: `FromJSON TraceEvent` is written out by hand instead of
+  derived. The three pre-existing kinds decode exactly as before; a
+  `call_evidence` line fails to parse with a message saying to read it as a
+  plain `Data.Aeson.Value`. `ModelCallEvidence` has no `FromJSON` on purpose —
+  it embeds a `Cost` whose exact `Rational` amounts encode through an
+  approximating `Scientific`, so a decoder would return a different value than
+  was encoded — and manufacturing that fidelity would be the precise failure
+  this vocabulary exists to eliminate.
+
+- `baikai`: `Baikai.Trace.Sink.renderHuman` renders a `CallEvidence` event as a
+  single `EVIDENCE run=… call=… strength=…` line rather than the whole record. A
+  human-readable sink is for watching calls go by; the full record is meant to
+  be read out of `fileSink` output by a machine.
+
+- `baikai`: call identifiers on the trace path are now globally unique.
+  `Baikai.Evidence.newCallId` produces 32 lowercase hexadecimal characters
+  carrying 128 bits — 48 bits of Unix time in milliseconds, 48 bits of a
+  per-process random seed drawn once from `/dev/urandom`, and a 32-bit counter.
+  The previous generator combined the process-start *second* with a
+  process-local counter into 16 characters, so two processes started within the
+  same second emitted identical identifier sequences; its own documentation
+  claimed only per-process uniqueness. Identifiers still sort chronologically
+  and are still not secrets.
+
+  `Baikai.Trace.newEventId` keeps its name and signature, delegates to
+  `newCallId`, and is now deprecated. Anything that pinned the 16-character
+  width — a log parser, a fixture, a column type — must widen to 32.
+
+- `baikai`: `renderCeilingViolation` no longer prints the raw provider arguments
+  a `ProviderArgsForbidden` violation carries. It reports how many were
+  requested and states that their values are not shown. Raw provider arguments
+  are the one part of a job description that can hold a credential — the
+  configuration layer classifies the setting secret for that reason — and a
+  refusal message that quoted them defeated the classification. The constructor
+  keeps its `[Text]` payload so a programmatic caller can still inspect it.
+
+## [baikai-claude 0.5.0.0] - 2026-08-05
+
+### Added
+
+- `baikai-claude`: new exposed module `Baikai.Provider.Claude.Agent` with
+  `ClaudeAgentConfig`, `defaultClaudeAgentConfig`, and `claudeAgentCommand`, a
+  pure renderer from an unattended `AgentRunRequest` to the `claude` argument
+  vector. It maps the capability profile onto `--permission-mode`
+  (`plan` / `acceptEdits` / `bypassPermissions`), joins a tool allow-list into
+  one `--allowedTools` argument, repeats `--add-dir` per extra directory, always
+  emits `-p`, and emits `--no-session-persistence` unless `persistSession` is
+  set. The prompt travels on standard input and appears nowhere in the argument
+  vector. A request naming a different provider is refused with
+  `ProviderMismatch`. Nothing is spawned.
+
+- `baikai-claude`: the Anthropic Messages provider now fills in the evidence
+  record it previously left blank. It records the model **Anthropic reported
+  running** (read from the `message_start` event, which the adapter already
+  decoded for the response id and then discarded), Anthropic's `request-id`
+  correlation header, the response id, the token counts Anthropic actually
+  reported, and a commitment digest over the assembled response. A field the
+  provider did not report stays `"unobserved"` and is never backfilled from the
+  request — in particular, a stream that fails before `message_start` reports no
+  observed model at all. `strength` is `model_observed` when both the model and a
+  correlation identifier arrived, `correlated` when only the identifier did, and
+  `requested_only` otherwise; a 2xx status never raises it, because a 200 means
+  the request was accepted, not that any particular model ran.
+  `fully_observed` is unreachable on this transport, since Anthropic does not
+  echo the thinking configuration it applied.
+
+- `baikai-claude`: an evidence record's `thinking` field now describes what the
+  caller's reasoning-effort preference actually became on the wire, including
+  three downgrades that were previously invisible everywhere in baikai's output:
+  asking for thinking on a model that does not advertise `reasoning`
+  (`thinking_dropped_unsupported_model`); asking for a level whose token budget
+  does not fit under the resolved output-token ceiling
+  (`thinking_dropped_budget_exceeded`, carrying both colliding numbers), which is
+  reachable by lowering `maxTokens` alone; and asking for `high` on an
+  adaptive-thinking model, which sends no effort field and so is
+  wire-indistinguishable from taking Anthropic's default depth
+  (`effort_omitted`). `minimal` on an adaptive model reports `effort_clamped`,
+  because Anthropic's adaptive vocabulary has no `minimal`.
+
+- `baikai-claude`: new exports from `Baikai.Provider.Claude.Sse` —
+  `ResponseMetadata` and `capturedHeaderNames` — and from
+  `Baikai.Provider.Claude.Api` — `claudeMessagesStreamWith`, `SseDriver`, and
+  `anthropicStrength`. Response-header capture is an **allow-list**
+  (`request-id`, `x-request-id`, `cf-ray`, in that preference order), not a
+  denylist, so a header a future gateway adds is not recorded by default.
+
+- `baikai-claude` and `baikai-openai`: both subprocess providers now fill in the
+  evidence record they previously left blank, and both export the translation
+  function that describes it — `claudeCliThinking` and `codexCliThinking`. They
+  record the session or thread identifier the tool reported, the token counts it
+  reported, the model it named when it names one, the resolved executable path
+  in place of an endpoint URL, the tool's own `--version` string as the
+  implementation version (for this transport the tool *is* the implementation),
+  a request commitment over the rendered argument vector, and a response
+  commitment over the assembled answer.
+
+  **A zero exit status never raises the strength.** A coding-agent CLI that
+  exits zero has demonstrated that it ran and did not crash; it has not stated
+  which model served the request. Subprocess calls almost always exit zero, so
+  encoding that as corroboration would make the weakest evidence in the system
+  look like the strongest. `strength` is `model_observed` only when the tool
+  named both an identifier and a model, `correlated` when it named only an
+  identifier, and `requested_only` otherwise.
+
+  The two transports differ in how far they can get. `claude` names the model
+  that consumed tokens in its result event's `modelUsage` map, complete with a
+  context-window variant marker such as `[1m]`, so a Claude CLI run can reach
+  `model_observed`. `codex-cli 0.146.0` names no model anywhere in its event
+  stream, so **no** Codex CLI run can exceed `correlated` — backfilling the
+  `--model` flag baikai passed would report the request as an observation.
+
+- `baikai-claude`: an evidence record's `thinking` field now describes what a
+  reasoning-effort request became on the `claude` command line: mode `flag`,
+  wire field `--effort`, and an `effort_clamped` adjustment recording the
+  `minimal` → `low` collapse, because the tool's `--effort` flag has no
+  `minimal`. A caller asking for `minimal` and a caller asking for `low` produce
+  byte-identical argument vectors — and therefore identical request commitment
+  digests — so the translation is the only place that difference survives.
+
+- **Breaking:** `baikai-claude` and `baikai-openai`: `claudeAgentCommand` and
+  `codexAgentCommand` return `(AgentCommand, ThinkingTranslation)` rather than
+  `AgentCommand`. The runner deliberately imports no vendor renderer, so it
+  cannot derive the translation and has to be handed it. A caller that only
+  wants the command writes `fmap fst`. Both modules also export the translation
+  function alone — `claudeAgentThinking` and `codexAgentThinking` — for asking
+  what a level would become without rendering anything.
+
+### Fixed
+
+- **Loud:** `baikai-claude` and `baikai-openai`: both subprocess providers
+  hardcoded `usage = zeroUsage` on every call, so a cost dashboard saw every
+  `claude -p` and `codex exec` call as consuming no tokens and costing nothing.
+  Both tools report their own token counts and baikai now carries them through,
+  normalized into the disjoint `Usage` convention: `claude`'s counts are
+  Anthropic-shaped and already disjoint, while `codex` reports OpenAI-style
+  inclusive prompt counts, so its cached tokens are subtracted out of
+  `inputTokens`. `claude` additionally reports a `total_cost_usd`, which now
+  populates `Usage.cost` exactly rather than being reported as zero.
+
+  **A dashboard that read these calls as free will now see real tokens and, for
+  `claude`, a real cost.** That is the correction, not a regression — but it
+  changes what existing reports show, and totals over historical data will not
+  match totals over new data.
+
+- `baikai-claude`: `Response.responseId` was always `Nothing` on the `claude -p`
+  transport even though `ClaudeCliResult` decoded the tool's `session_id` one
+  screen earlier and then dropped it. It now carries that identifier, on both
+  the successful and the failed terminal. `baikai-openai`: the same for
+  `codex exec`, whose thread identifier was filtered out of the event stream
+  along with everything that was not an `agent_message`. These are the handles
+  each vendor's support tooling looks a run up by.
+
+### Changed
+
+- **Breaking:** `baikai-claude`: `Baikai.Provider.Claude.Sse`'s four streaming
+  entry points — `claudeSseStream`, `claudeSseStreamValue`,
+  `claudeSseStreamValueWithHeaders`, and `sseFromResponse` — take a new
+  `ResponseMetadata -> IO ()` callback immediately before the existing per-event
+  callback. It fires exactly once, before the first event, on both the success
+  and the non-2xx path. Pass `(\_ -> pure ())` to keep the previous behaviour.
+  The callback is separate rather than a widening of the per-event one because
+  the per-event callback runs once per SSE frame and response-level data does not
+  belong on that path.
+
+- **Breaking:** `baikai-claude`: `Baikai.Provider.Claude.Internal.Request`'s
+  `mapRequest` now returns
+  `Either Text (Messages.CreateMessage, ThinkingTranslation)` and
+  `computeThinking` returns `(ThinkingPlan, ThinkingTranslation)`. Take `fst` to
+  keep the previous value. This module is exposed for provider tests and
+  debugging and its header states it is not covered by PVP compatibility
+  guarantees, but the change is recorded here because that is not a licence to
+  break a consumer silently.
+
+- **Breaking:** `baikai-claude`: `claudeInteractiveCommand` now returns
+  `Either AgentRenderError (FilePath, [String])` and `launchClaudeInteractive`
+  returns `IO (Either AgentRenderError InteractiveLaunchResult)`. A request
+  whose `safety` is a `CodexSandbox` policy — which Claude Code cannot express
+  — is refused with `SafetyNotExpressible AgentClaude`, naming the rejected
+  sandbox mode and approval policy and suggesting `ClaudeAllowedTools` or
+  `DefaultSafety`. Previously the policy was silently discarded and an
+  **unrestricted** Claude session was started and reported as a success. A
+  `Left` means no process was started; a `Right` with a non-zero exit code
+  means the session ran and exited non-zero. `DefaultSafety` and an empty
+  `ClaudeAllowedTools` list still render no safety flag and are never refused,
+  and no previously rendered argument vector changed. Callers must handle the
+  refusal branch.
+
+## [baikai-openai 0.5.0.0] - 2026-08-05
+
+### Added
+
+- `baikai-openai`: new exposed module `Baikai.Provider.OpenAI.Agent` with
+  `CodexAgentConfig`, `defaultCodexAgentConfig`, and `codexAgentCommand`, the
+  same renderer for `codex exec`. It maps the capability profile onto
+  `--sandbox` (`read-only` / `workspace-write` / `danger-full-access`), emits
+  `--cd` for the working root, and defaults `--skip-git-repo-check` and
+  `--ephemeral` on. A request carrying a tool allow-list is **refused** with
+  `UnsupportedToolRestriction`, because `codex exec` has no such flag and running
+  it with unrestricted tools would grant more authority than the caller asked
+  for. Nothing is spawned.
+
+- `baikai-openai`: an evidence record's `thinking` field now describes what the
+  caller's reasoning-effort preference became on the wire for the specific host
+  the call went to, across **all seven** OpenAI-compatible wire shapes. The
+  OpenAI-native shape sends the canonical level verbatim and records no
+  adjustment, because it expresses every level exactly. The four shapes that
+  carry an effort word for a non-native host record `effort_clamped` whenever
+  the word differs from the canonical name — `minimal` becomes `low`, and both
+  `xhigh` and `max` become `high`. Z.ai and Qwen accept a bare
+  `enable_thinking: true` with no depth, so **every** level records
+  `effort_collapsed_to_toggle`: a caller asking for `max` and a caller asking
+  for `low` produce byte-identical requests there, and only the evidence record
+  can tell them apart. A host with no reasoning controls records
+  `thinking_dropped_unsupported_host` where the option previously vanished with
+  no trace. A forty-two-row table test pins the translation and the shaped
+  request body for every shape at every level.
+
+- `baikai-openai`: the Chat Completions provider now fills in the evidence record
+  it previously left blank. It records the model **the host reported running**
+  (read from the first streamed chunk carrying a top-level `model` field and
+  never overwritten by a later one), the host's `x-request-id` correlation
+  header, the response id, the token counts the host actually reported, and a
+  commitment digest over the assembled response. A field the host did not report
+  stays `"unobserved"` and is never backfilled from the request — in particular,
+  a call that fails before any chunk arrives reports no observed model at all.
+  `strength` is `model_observed` when both the model and a correlation
+  identifier arrived, `correlated` when only the identifier did, and
+  `requested_only` otherwise; a 2xx status never raises it, because a 200 means
+  the request was accepted, not that any particular model ran.
+  `fully_observed` is unreachable on this transport, since no host in this
+  ecosystem echoes the reasoning configuration it applied.
+
+- `baikai-openai`: new exports from `Baikai.Provider.OpenAI.Sse` —
+  `ResponseMetadata` and `capturedHeaderNames` — and from
+  `Baikai.Provider.OpenAI.Api` — `openaiChatStreamWith` and `SseDriver`.
+  Response-header capture is an **allow-list** (`x-request-id`, `request-id`,
+  `x-amzn-requestid`, `x-ms-request-id`, `cf-ray`, in that preference order),
+  not a denylist, so a header a future gateway adds is not recorded by default.
+  The list is longer than the Anthropic one because this transport speaks to an
+  open-ended set of hosts and the gateways commonly in front of them.
+
+- `baikai-openai`: the same field for `codex exec`: mode `flag`, wire field
+  `model_reasoning_effort`, and **no** adjustments at any level. Codex is the
+  only transport in baikai that expresses all six canonical levels exactly, and
+  a test asserts each one reaches the command line verbatim.
+
+### Fixed
+
+- `baikai-openai`: `Response.responseId` was always `Nothing` on the Chat
+  Completions transport, although every compatible host sends a top-level `id`
+  on every streamed chunk. It now carries the identifier the host reported, on
+  both the successful and the failed terminal.
+
+### Changed
+
+- **Breaking:** `baikai-openai`: `Baikai.Provider.OpenAI.Sse`'s four streaming
+  entry points — `openaiSseStream`, `openaiSseStreamValue`,
+  `openaiSseStreamValueWithHeaders`, and `sseFromResponse` — take a new
+  `ResponseMetadata -> IO ()` callback immediately before the existing per-chunk
+  callback. It fires exactly once, before the first chunk, on both the success
+  and the non-2xx path — a failed call's correlation identifier is if anything
+  more valuable than a successful one's. Pass `(\_ -> pure ())` to keep the
+  previous behaviour. The callback is separate rather than a widening of the
+  per-chunk one because that one runs once per SSE frame and response-level data
+  does not belong on that path.
+
+- **Breaking:** `baikai-openai`: `Baikai.Provider.OpenAI.Api`'s `RawChunk` gains
+  `model` and `responseId` fields, both `Maybe Text`. Code that pattern-matches
+  on `RawChunk` is unaffected; code that constructs one with record syntax must
+  add them.
+
+- **Breaking:** `baikai-openai`: `Baikai.Provider.OpenAI.Shape`'s
+  `shapeRequestBody`, `streamRequestBody`, and `injectThinkingShape` now return
+  `(Aeson.Value, ThinkingTranslation)` instead of a bare body. Take `fst` to
+  keep the previous value. The description has to travel out of the shaping step
+  because nothing downstream can recompute it: it depends on the host's
+  `ThinkingFormat`, which only the compat lookup knows. **No request body
+  changed** — every one of the seven shapes puts exactly the same bytes on the
+  wire as before.
+
+- **Breaking:** `baikai-openai`: `codexInteractiveCommand` now returns
+  `Either AgentRenderError (FilePath, [String])` and `launchCodexInteractive`
+  returns `IO (Either AgentRenderError InteractiveLaunchResult)`. A request
+  whose `safety` is a non-empty `ClaudeAllowedTools` list — which `codex` has
+  no flag for — is refused with `SafetyNotExpressible AgentCodex`, quoting the
+  rejected tools and suggesting `CodexSandbox` or `DefaultSafety`. Previously
+  the allow-list was silently discarded and Codex was started with its default
+  sandbox. The same `Left`/`Right` reading applies, `DefaultSafety` and an
+  empty allow-list are never refused, and no previously rendered argument
+  vector changed. Callers must handle the refusal branch.
+
+  Both changes make the interactive surface honor the same contract as the new
+  unattended surface: a safety policy the chosen provider cannot express fails
+  visibly instead of silently becoming a weaker policy. Downstream consumers
+  must adapt before upgrading; the known one is `shinzui/seihou`, whose
+  `Seihou.CLI.AgentLaunchExec` module builds interactive launch requests.
+
+## [baikai-trace-otel 0.3.0.3] - 2026-08-05
+
+### Added
+
+- `baikai-trace-otel`: the sink attaches an evidence record's salient fields to
+  the open span as flat attributes (`baikai.evidence.run_id`,
+  `baikai.evidence.call_id`, `baikai.evidence.strength`, the two digests, and
+  `gen_ai.response.model` only when the provider actually reported one) rather
+  than serialising the record into one blob. A `CallEvidence` event neither
+  opens nor closes a span.
+
+### Changed
+
+- `baikai-trace-otel`: widened its `baikai` bound to admit `0.5`. No API change.
+
+## [baikai-effectful 0.3.0.3] - 2026-08-05
+
+### Changed
+
+- Widened its `baikai` bound to admit `0.5`. No API change; the package's
+  own surface is untouched.
+
+## [baikai-kit 0.1.0.4] - 2026-08-05
+
+### Changed
+
+- Widened its `baikai` bound to admit `0.5`. No API change; the package's
+  own surface is untouched.
+
+## [baikai-agent 0.1.0.0] - 2026-08-05
+
+### Added
+
+- `baikai-agent`: **new package** (`0.1.0.0`) holding the unattended
+  coding-agent runner. `Baikai.Agent.Run.runAgentCommand` takes an
+  `AgentRunRequest` and an already-rendered `AgentCommand` and spawns the tool
+  with no terminal and no human present. It delivers the prompt on standard
+  input and closes the handle, drains standard output and standard error
+  concurrently so a chatty agent cannot deadlock on a full pipe, retains at most
+  `outputLimit` bytes per stream while reading and discarding the excess, and
+  honors the three output disciplines. Preconditions run before any spawn: a
+  missing working directory is `WorkingDirMissing` and unset or empty declared
+  variables are `MissingEnvironment`, listing all of them at once. On timeout
+  the child's whole process group is interrupted, given a grace period, and then
+  terminated, so the agent's own child processes go with it; the failure reports
+  the configured limit. A non-zero exit code is a successful run carrying that
+  code, not a failure. The runner consumes an already-rendered `AgentCommand`
+  and never imports a vendor renderer, so it is exercised entirely with
+  hand-written argument vectors. Its POSIX-signal escalation is conditional on a
+  non-Windows build.
+
+- `baikai-agent`: new exposed module `Baikai.Agent.Config`, the layered
+  configuration layer. `resolveAgentJob` resolves one named job across five
+  layers — built-in defaults, the operator file, the repository file, the
+  environment, then command-line overrides, later layers winning — and returns
+  the resolved `AgentJob` together with a report attributing every value to the
+  file, line, and column it came from. `agentJobRequest` converts a job into an
+  `AgentRunRequest`, taking the prompt at call time. `listAgentJobs` enumerates
+  configured job names, sorted, each attributed to the highest-precedence scope
+  defining it. `defaultAgentConfigPaths` locates
+  `$XDG_CONFIG_HOME/baikai/agents.kdl` (or `$HOME/.config/baikai/agents.kdl`)
+  and `./.baikai/agents.kdl`, with no upward search through parent directories.
+
+  The **policy ceiling** is loaded by a separate function, `loadAgentCeiling`,
+  against a separate source list containing the operator file and nothing else:
+  no repository file, environment variable, or command-line override can raise
+  it. `applyCeilingToJob` refuses an over-broad request with `CeilingRejected`
+  rather than clamping it. With no operator file the ceiling is
+  `defaultAgentCeiling`. `safety.provider-args` is classified secret and renders
+  as `<redacted>` in any report or structured error.
+
+  New dependencies: `settei`, `settei-env`, `settei-kdl`, and
+  `settei-optparse-applicative` (all `^>=0.2`, published on Hackage at
+  `0.2.0.0`), plus `containers` and `filepath`. `settei-formats` is deliberately
+  excluded, because it bundles Dhall loading and repository configuration is
+  untrusted input here.
+
+- `baikai-agent`: the **`baikai` executable**, with the `agent run`,
+  `agent show`, and `agent list` commands, and the `Baikai.Agent.Cli` module
+  that implements them. A shell script now invokes one stable command, supplies
+  a prompt on standard input, and selects Claude Code or Codex entirely through
+  configuration.
+
+  `agent run` resolves the named job, caps it against the operator ceiling,
+  renders it through the vendor renderer for its provider, and spawns it. The
+  agent's own exit code passes through unchanged; Baikai's own failures use 64
+  and above following the `sysexits` convention — 64 for a usage error or an
+  empty prompt, 69 when the executable could not be started, 70 for malformed
+  output, 75 for a timeout, 77 for a policy refusal, and 78 for a configuration
+  problem. The prompt comes from `--prompt-stdin`, `--prompt-file`, or
+  `--prompt`, which are mutually exclusive, and is decoded as UTF-8 explicitly
+  rather than through the handle's locale encoding.
+
+  `agent show` performs the whole pipeline except spawning and prints each
+  resolved value with the file, line, and column it came from, the policy
+  ceiling in force and where it was read, and the exact argument vector that
+  would be spawned — with `<redacted>` in place of any raw provider argument. A
+  job whose policy is refused prints its configuration first and then the
+  refusal. `agent list` enumerates configured jobs and the scope each came from.
+
+  Every Baikai diagnostic goes to standard error. The agent's own output follows
+  the job's output mode, so `response=$(baikai agent run job)` yields the
+  agent's answer alone for a capturing job. `--set KEY=VALUE` overrides one
+  setting of the selected job through `settei`'s own command-line source, so an
+  override is attributed with the same fidelity as a file. `--json` emits
+  exactly one JSON object per command.
+
+  New dependencies for `baikai-agent`: `baikai-claude`, `baikai-openai`, and
+  `optparse-applicative`. The provider packages are needed only so that
+  `renderJobCommand`, the single provider dispatch point in the codebase, can
+  reach both renderers. This is the first dependency in the workspace from
+  `baikai-agent` onto the provider packages, so `baikai-agent` now publishes
+  after all three of `baikai`, `baikai-claude`, and `baikai-openai`.
+
+  The user guide `docs/user/unattended-agent-runs.md` documents the whole
+  surface: the three commands with their flags, exit codes, and stream
+  discipline; the KDL job format and layer precedence; the operator ceiling and
+  redaction; the capability mapping tables for both tools; and a before-and-after
+  migration of a script that embeds provider flags today.
+  `docs/user/cli-providers.md` and `docs/user/interactive-launches.md` link to
+  it, and the capability mapping tables moved there from the latter.
+
+- `baikai-agent`: **an unattended coding-agent run now produces model-call
+  evidence.** This surface previously had no observability of any kind: no trace
+  sink, no `Response`, no usage, no identifiers. An operator could show that a
+  process started, exited, and took some time; they could not show which model
+  ran, which reasoning effort was applied, or which agent session the run
+  corresponds to in the vendor's records.
+
+  A record carries the run and call identifiers, the resolved executable and its
+  own reported version, digests over the request, the requested model and what
+  the reasoning-effort request became on the command line, whatever the tool
+  reported about itself, the outcome, and an honest strength.
+
+  **A zero exit status never raises the strength.** On this surface that rule
+  matters more than anywhere else, because almost every unattended run exits
+  zero. A coding agent that exits zero has demonstrated that it ran, not which
+  model served it.
+
+  Two things gate what a record can prove, and neither is the default. The job
+  must **capture** output — under `inherit` the agent's bytes went to the
+  operator's terminal and baikai never held them — and the tool must be
+  configured to print a structured format, which means `--output-format json`
+  for `claude` or `--json` for `codex exec` through the job's `provider-args`.
+  Without both, the tool's session identifier, model, and token counts are
+  genuinely unavailable and the record says `"unobserved"` rather than inferring
+  anything. A timed-out run records `aborted`; a run that never started records
+  nothing at all.
+
+- **Breaking:** `baikai-agent`: `Baikai.Agent.Run.runAgentCommand` takes two new
+  leading arguments and returns the new outcome type:
+  `Maybe EvidenceRequest -> ThinkingTranslation -> AgentRunRequest -> AgentCommand -> IO AgentRunOutcome`.
+  A caller who wants the previous behaviour passes `Nothing` and
+  `Baikai.Evidence.noThinkingRequested` and reads the `outcome` field; that path
+  is byte-for-byte what it was, and costs what it cost — no digest is computed,
+  no call identifier is generated, and the tool is not invoked a second time to
+  read its version.
+
+- `baikai-agent`: `baikai agent run` gains `--evidence-file PATH` and
+  `--run-id TEXT`. Supplying neither leaves the run on the pre-existing path at
+  the pre-existing cost; supplying either turns recording on, with the job's own
+  name standing in as the run identifier when only a destination is given. The
+  file is written atomically — a staging file beside the destination, then a
+  rename — so a reader polling the path never sees a half-written object, and it
+  is never appended to. A failed write is reported on standard error and never
+  changes the exit code, because the agent's own status is what a calling script
+  branches on. `docs/user/unattended-agent-runs.md` documents both options and,
+  more importantly, what the record does and does not prove.
+
+- `baikai-agent`: `baikai agent run` gains `--require-evidence STRENGTH`, taking
+  `requested_only`, `correlated`, `model_observed`, or `fully_observed` — the
+  same words a record's `strength` field spells, so what one record showed can
+  be passed back as the next run's requirement. A job whose configuration cannot
+  produce evidence of at least that strength is refused before anything is
+  spawned, exiting 77 — the code a ceiling violation and an inexpressible safety
+  policy already use, so a script branching on 77 needs no new case.
+
+## [baikai-claude 0.4.0.1] - 2026-07-30
+
+### Fixed
+
+- Widened the `crypton` bound from `^>=1.0` to `>=1.0 && <1.2` so consumers can
+  build `baikai-claude` alongside packages that require `crypton` 1.1.x (for
+  example `pg-migrate-1.1.0.0`), which previously had no solvable build plan.
+  The only `crypton` use is `Crypto.Hash` (`Digest`, `SHA256`) in
+  `Baikai.Provider.Claude.Transport`, whose API is identical across the 1.0/1.1
+  boundary. No API change.
+
+## [baikai 0.4.1.0] - 2026-07-20
+
+### Changed
+
+- Version bump only; no library API or code changes. Released so the umbrella
+  release tag `baikai-0.4.1.0` names a fresh core version alongside the breaking
+  `baikai-claude` / `baikai-openai` 0.4.0.0 releases, matching the tag
+  convention downstream consumers pin against.
+
+## [baikai-claude 0.4.0.0] - 2026-07-20
+
+### Changed
+
+- **Breaking:** `claudeCliCommand` now takes the `Options` record and forwards
+  `Options.thinking` to batch `claude -p` as `--effort <level>` (`minimal`
+  collapses to `low`, matching the interactive launcher and the claude CLI's
+  lack of a `minimal` value). `thinking = Nothing` emits no effort flag, keeping
+  existing argv byte-for-byte. The added parameter is a PVP-major signature
+  change.
+
+## [baikai-openai 0.4.0.0] - 2026-07-20
+
+### Changed
+
+- **Breaking:** `codexCliCommand` now takes the `Options` record and forwards
+  `Options.thinking` to `codex exec` as `-c model_reasoning_effort=<level>` for
+  all six effort levels. `thinking = Nothing` emits no override, keeping
+  existing argv byte-for-byte. The added parameter is a PVP-major signature
+  change.
+
+## [baikai 0.4.0.0] - 2026-07-20
+
+### Added
+
+- Added `ThinkingXHigh` and `ThinkingMax` to the exported `ThinkingLevel`
+  vocabulary and added a defaulted `InteractiveLaunchRequest.effort` field.
+  Extending the closed sum type is a PVP-major API change for downstream
+  exhaustive matches.
+
+## [baikai-claude 0.3.0.2] - 2026-07-20
+
+### Added
+
+- Added `--effort` rendering to interactive Claude Code launches and preserved
+  `xhigh` / `max` on native adaptive Anthropic API requests, with larger fixed
+  budgets for manual-thinking models.
+
+### Changed
+
+- Bumped the internal `baikai` dependency bound to `^>=0.4.0` for the
+  baikai 0.4.0.0 release.
+
+## [baikai-openai 0.3.0.2] - 2026-07-20
+
+### Added
+
+- Added `model_reasoning_effort` overrides to interactive Codex launches and
+  preserved `xhigh` / `max` in native OpenAI request JSON; non-native
+  OpenAI-compatible request shapes continue to clamp them to `high`.
+
+### Changed
+
+- Bumped the internal `baikai` dependency bound to `^>=0.4.0` for the
+  baikai 0.4.0.0 release.
+
+## [baikai-trace-otel 0.3.0.2] - 2026-07-20
+
+### Changed
+
+- Bumped the internal `baikai` dependency bound to `^>=0.4.0` for the
+  baikai 0.4.0.0 release. No API changes.
+
+## [baikai-effectful 0.3.0.2] - 2026-07-20
+
+### Changed
+
+- Bumped the internal `baikai` dependency bound to `^>=0.4.0` for the
+  baikai 0.4.0.0 release. No API changes.
+
+## [baikai-kit 0.1.0.3] - 2026-07-20
+
+### Changed
+
+- Bumped the internal `baikai` dependency bound to `^>=0.4.0` for the
+  baikai 0.4.0.0 release. No API changes.
+
+## [baikai 0.3.1.0] - 2026-07-15
+
+### Added
+
+- Added `claude-sonnet-5` to the Anthropic model catalog (1M context window,
+  128k max output, `tool_call` + reasoning).
+- Added the `gpt-5.6` family — `gpt-5.6`, `gpt-5.6-luna`, `gpt-5.6-sol`, and
+  `gpt-5.6-terra` — to the OpenAI model catalog (chat-completions with
+  `tool_call` support).
+
+### Changed
+
+- Corrected `claude-sonnet-4-5` context window to 1M tokens and
+  `claude-sonnet-4-6` max output to 128k tokens in the catalog.
+- Added PVP-compliant upper bounds to all previously-unbounded library and
+  executable dependencies.
+
+## [baikai-claude 0.3.0.1] - 2026-07-15
+
+### Changed
+
+- Added PVP-compliant upper bounds to all previously-unbounded library and
+  executable dependencies.
+
+## [baikai-openai 0.3.0.1] - 2026-07-15
+
+### Changed
+
+- Added PVP-compliant upper bounds to all previously-unbounded library and
+  executable dependencies.
+
+## [baikai-trace-otel 0.3.0.1] - 2026-07-15
+
+### Changed
+
+- Added PVP-compliant upper bounds to all previously-unbounded library and
+  executable dependencies.
+
+## [baikai-effectful 0.3.0.1] - 2026-07-15
+
+### Changed
+
+- Added PVP-compliant upper bounds to all previously-unbounded library and
+  executable dependencies.
+
+## [baikai-kit 0.1.0.2] - 2026-07-15
+
+### Changed
+
+- Added PVP-compliant upper bounds to all previously-unbounded library and
+  executable dependencies.
+
+## [baikai 0.3.0.0] - 2026-07-03
+
+### Added
+
+- Added the documented record-update bases `emptyOptions`, `emptyContext`,
+  `emptyModel`, `emptyResponse`, `emptyTool`, `emptyTextContent`,
+  `emptyThinkingContent`, `emptyToolCall`, `emptyImageContent`,
+  `emptyEmbeddingModel`, plus zero-valued bases `zeroUsage`, `zeroCost`,
+  `zeroCostBreakdown`, and `zeroModelCost`.
+- Added `firstEmbedding`, a total accessor for OpenAI-compatible embedding
+  responses.
+- Added `responseError`, `errorResponse`, `httpError`, and
+  `parseRetryAfterSeconds` for the in-band error contract.
+
+### Changed
+
+- **Breaking:** Constructors for evolvable records are no longer exported:
+  `Options`, `Context`, `Model`, `OpenAICompletionsCompat`,
+  `AnthropicMessagesCompat`, and `InteractiveLaunchRequest` are built from
+  exported base values plus record updates.
+- **Breaking:** The `_X` base values are deprecated in favor of the new
+  `empty*` and `zero*` names; the aliases remain for this release.
+- **Breaking:** Removed `unModel`; use `mkModel` or `emptyModel` record
+  updates.
+- **Breaking:** Renamed `InteractiveLaunchRequest.model` to `modelId`.
+- **Breaking:** `Response.latencyMs` and trace event `latencyMs` fields are
+  now `Int`.
+- **Breaking:** `completeRequest` / `completeRequestWith` no longer throw
+  `BaikaiError` for unregistered API tags; they return an error-shaped
+  `Response`.
+- **Breaking:** CLI providers now report subprocess/decode/provider failures
+  in-band as error-shaped `Response`s.
+- **Breaking:** `errorTerminal` now requires a `BaikaiError`, enforcing
+  structured error details for `EventError` construction sites.
+- Documented that `Baikai.Prelude` is a convenience module outside the PVP
+  stability contract and that `.Internal` modules have no compatibility
+  guarantees.
+
+### Fixed
+
+- Empty embedding `data` arrays now produce a typed `decodeError` instead of
+  crashing on an empty vector.
+- The model-fetch JSON renderer now delegates string escaping to aeson.
+- The model generator now fails on sanitized Haskell identifier collisions
+  instead of rendering duplicate bindings.
+- Live HTTP status, `Retry-After`, and network-failure classification now
+  works on both API providers.
+- `content_filter` / Anthropic refusals terminate as classified `EventError`
+  terminals, and `liftCompleteToStream` preserves error-shaped responses.
+
+## [baikai-claude 0.3.0.0] - 2026-07-03
+
+### Changed
+
+- **Breaking:** `Baikai.Provider.Claude.ErrorClass` moved to
+  `Baikai.Provider.Claude.Internal.ErrorClass`.
+- **Breaking:** `mapRequest` and pure request-shaping helpers moved from
+  `Baikai.Provider.Claude.Api` to
+  `Baikai.Provider.Claude.Internal.Request`.
+- **Breaking:** `ClaudeCliConfig` and `ClaudeInteractiveConfig` constructors
+  are no longer exported; start from their default config values and update
+  fields.
+- **Breaking:** CLI and interactive `extraArgs` fields are now `[Text]`.
+
+## [baikai-openai 0.3.0.0] - 2026-07-03
+
+### Changed
+
+- **Breaking:** `Baikai.Provider.OpenAI.ErrorClass` moved to
+  `Baikai.Provider.OpenAI.Internal.ErrorClass`.
+- **Breaking:** `mapRequest` and pure request-shaping helpers moved from
+  `Baikai.Provider.OpenAI.Api` to
+  `Baikai.Provider.OpenAI.Internal.Request`.
+- **Breaking:** `CodexCliConfig` and `CodexInteractiveConfig` constructors are
+  no longer exported; start from their default config values and update fields.
+- **Breaking:** CLI and interactive `extraArgs` fields are now `[Text]`.
+
+## [baikai-trace-otel 0.3.0.0] - 2026-07-03
+
+### Changed
+
+- Updated the `baikai` dependency bound to `^>=0.3.0`.
+- Adjusted to the core trace event `latencyMs :: Int` type.
+
+## [baikai-effectful 0.3.0.0] - 2026-07-03
+
+### Changed
+
+- Updated the `baikai` dependency bound to `^>=0.3.0`.
+
+## [baikai-kit 0.1.0.1] - 2026-07-03
+
+### Changed
+
+- Updated the `baikai` dependency bound to `^>=0.3.0`.
+
+## [baikai 0.2.0.0] - 2026-06-21
+
+### Added
+
+- `Usage`, `Cost`, and `CostBreakdown` now have `Semigroup`/`Monoid`
+  instances that add field-by-field, plus `sumUsage :: Foldable f => f
+  Usage -> Usage`, so callers can total per-call usage and cost.
+  `reasoningTokens` combines as presence-wins (`Nothing` only when both
+  operands are `Nothing`).
+- A categorised error model: `BaikaiError` is now a record carrying an
+  `ErrorCategory` (`AuthError`, `RateLimited`, `ContextOverflow`,
+  `InvalidRequest`, `TransientError`, `DecodeFailure`, `ProcessFailure`,
+  `ProviderUnavailable`, `OtherError`), an optional HTTP `httpStatus`, a
+  `retryAfterSeconds` hint, and a subprocess `exitCode`. New smart
+  constructors (`providerError`, `invalidRequest`, `decodeError`,
+  `processError`, `rateLimited`, `authError`, `providerUnavailable`),
+  the `isRetryable` predicate, and the pure `classifyHttpStatus` /
+  `classifyHttpStatusWithBody` helpers let callers implement retry
+  policy without parsing error text. `ErrorCategory` and `BaikaiError`
+  serialize to JSON.
+- `Response` and the streaming `EventError`'s `TerminalPayload` now
+  carry `errorInfo :: Maybe BaikaiError`, so a failed `completeRequest`
+  (or a drained stream) exposes the structured category/retry hint
+  in-band. `Baikai.Stream.Event` gains `doneTerminal` / `errorTerminal`
+  constructors.
+
+### Changed
+
+- **Breaking:** `BaikaiError`'s four flat constructors
+  (`ProviderError`, `RequestInvalid`, `DecodeError`, `ProcessError`)
+  were replaced by the record above. Migrate by lowercasing to the
+  smart constructors — `ProviderError "x"` becomes `providerError "x"`,
+  `ProcessError n "x"` becomes `processError n "x"`, etc.
+- **Breaking:** `Baikai.Stream.Event.TerminalPayload` and
+  `Baikai.Response.Response` gained an `errorInfo` field; build
+  `TerminalPayload` via `doneTerminal` / `errorTerminal`.
+
+### Fixed
+
+- Restored JSON decoding for `BaikaiError` values with omitted optional
+  metadata fields.
+
+## [baikai-claude 0.2.0.0] - 2026-06-21
+
+### Added
+
+- The Anthropic API and `claude -p` CLI providers now classify failures
+  into the typed `BaikaiError` categories: HTTP errors (via the caught
+  `servant-client` `ClientError`) map status/`Retry-After`/body onto
+  `AuthError` / `RateLimited` / `ContextOverflow` / `InvalidRequest` /
+  `TransientError`, and mid-stream Anthropic `error` events are
+  classified by their error type. The result is surfaced on
+  `Response.errorInfo`.
+
+## [baikai-openai 0.2.0.0] - 2026-06-21
+
+### Added
+
+- The OpenAI/OpenAI-compatible API and `codex exec` CLI providers now
+  classify failures into the typed `BaikaiError` categories the same way
+  as `baikai-claude` (HTTP `ClientError` for status-based errors,
+  streamed error text for mid-stream errors), surfaced on
+  `Response.errorInfo`.
+
+## [baikai-trace-otel 0.2.0.0] - 2026-06-21
+
+### Changed
+
+- Updated the `baikai` dependency bound to `^>=0.2.0` for compatibility with
+  the `baikai 0.2.0.0` breaking API release.
+
+## [baikai-effectful 0.2.0.0] - 2026-06-21
+
+### Changed
+
+- Updated the `baikai` dependency bound to `^>=0.2.0` for compatibility with
+  the `baikai 0.2.0.0` breaking API release.
+
+## [baikai 0.1.1.0] - 2026-06-12
+
+### Added
+
+- Added provider-agnostic `ResponseFormat` support on `Options`, including
+  plain JSON-object mode and named JSON-schema mode.
+- Added `Baikai.Embedding`, an OpenAI `/v1/embeddings` client for text
+  embeddings.
+
+## [baikai-claude 0.1.1.0] - 2026-06-12
+
+### Added
+
+- Mapped baikai `ResponseFormat` options onto Anthropic `output_config` for
+  Claude API requests.
+- Exported `mapRequest` for request-mapping tests and downstream inspection.
+
+## [baikai-openai 0.1.1.0] - 2026-06-12
+
+### Added
+
+- Mapped baikai `ResponseFormat` options onto OpenAI Chat Completions
+  `response_format`.
+- Exported `mapRequest` for request-mapping tests and downstream inspection.
+
+## [baikai-effectful 0.1.0.0] - 2026-06-12
+
+### Added
+
+- Initial release: effectful binding for baikai with the `Baikai` dynamic
+  effect, `complete`, `streamCollect`, `streamEach`, and registry-backed
+  interpreters.
+
+## [baikai 0.1.0.0] - 2026-06-04
+
+### Added
+
+- Initial release: unified Haskell interface for working with multiple AI
+  providers. Core modules including `Baikai`, `Baikai.Prelude`, `Baikai.Api`,
+  `Baikai.Provider`, `Baikai.Provider.Registry`, `Baikai.Response`,
+  `Baikai.Stream`, `Baikai.Tool`, `Baikai.Trace`, and the cost/usage modules.
+- Depends on released `streamly` (`>=0.11 && <0.13`) and `streamly-core`
+  (`>=0.3 && <0.5`) from Hackage, so all dependencies resolve from Hackage.
+
+## [baikai-claude 0.1.0.0] - 2026-06-04
+
+### Added
+
+- Initial release: Anthropic Claude providers for the baikai abstraction,
+  wrapping the `claude` package for both the Anthropic API and the `claude -p`
+  CLI (`Baikai.Provider.Claude.Api`, `.Cli`, `.Interactive`).
+
+## [baikai-openai 0.1.0.0] - 2026-06-04
+
+### Added
+
+- Initial release: OpenAI providers for the baikai abstraction, wrapping the
+  `openai` package for OpenAI's Chat Completions API
+  (`Baikai.Provider.OpenAI.Api`, `.Cli`, `.Interactive`).
+
+## [baikai-trace-otel 0.1.0.0] - 2026-06-04
+
+### Added
+
+- Initial release: OpenTelemetry `TraceSink` adapter for baikai
+  (`Baikai.Trace.Sink.OpenTelemetry`), emitting one OTel span per provider call
+  with GenAI semantic-convention attributes plus baikai cost and latency.
diff --git a/baikai-kit.cabal b/baikai-kit.cabal
--- a/baikai-kit.cabal
+++ b/baikai-kit.cabal
@@ -1,19 +1,21 @@
-cabal-version: 3.4
-name:          baikai-kit
-version:       0.1.0.4
-synopsis:      Shared kit installer for AI-agent skills and subagents
+cabal-version:   3.4
+name:            baikai-kit
+version:         0.2.0.0
+synopsis:        Shared kit installer for AI-agent skills and subagents
 description:
   Shared implementation of kit listing, installation, update, uninstall,
   status, and discovery helpers for command-line tools that install local
   AI-agent skills and subagents.
 
-category:      AI
-license:       BSD-3-Clause
-license-file:  LICENSE
-author:        Nadeem Bitar
-maintainer:    nadeem@gmail.com
-copyright:     (c) 2026 Nadeem Bitar
-build-type:    Simple
+category:        AI
+license:         BSD-3-Clause
+license-file:    LICENSE
+author:          Nadeem Bitar
+maintainer:      nadeem@gmail.com
+copyright:       (c) 2026 Nadeem Bitar
+build-type:      Simple
+tested-with:     GHC ==9.12.4
+extra-doc-files: CHANGELOG.md
 
 common common-options
   ghc-options:
@@ -51,6 +53,7 @@
     Baikai.Kit
     Baikai.Kit.Command
     Baikai.Kit.Config
+    Baikai.Kit.Error
     Baikai.Kit.Install
     Baikai.Kit.Manifest
     Baikai.Kit.Path
@@ -61,7 +64,7 @@
 
   build-depends:
     , aeson                 ^>=2.2
-    , baikai                ^>=0.5.0
+    , baikai                ^>=0.6.0
     , base                  >=4.20   && <5
     , binary                ^>=0.8
     , bytestring            ^>=0.12
diff --git a/src/Baikai/Kit.hs b/src/Baikai/Kit.hs
--- a/src/Baikai/Kit.hs
+++ b/src/Baikai/Kit.hs
@@ -1,6 +1,7 @@
 module Baikai.Kit
   ( module Baikai.Kit.Command,
     module Baikai.Kit.Config,
+    module Baikai.Kit.Error,
     module Baikai.Kit.Install,
     module Baikai.Kit.Manifest,
     module Baikai.Kit.Path,
@@ -13,6 +14,7 @@
 
 import Baikai.Kit.Command
 import Baikai.Kit.Config
+import Baikai.Kit.Error
 import Baikai.Kit.Install
 import Baikai.Kit.Manifest
 import Baikai.Kit.Path
diff --git a/src/Baikai/Kit/Command.hs b/src/Baikai/Kit/Command.hs
--- a/src/Baikai/Kit/Command.hs
+++ b/src/Baikai/Kit/Command.hs
@@ -1,20 +1,42 @@
+-- | The optparse-applicative adapter a consuming tool wires up as its
+--   @kit@ subcommand.
+--
+--   'runKit' is the only function in @baikai-kit@ that exits the process;
+--   see @docs/adr/0013-library-code-never-calls-exitfailure.md@.
 module Baikai.Kit.Command
   ( KitCommand (..),
     kitCommandParser,
     runKit,
+    runKitCommand,
   )
 where
 
-import Baikai.Kit.Config (KitConfig, KitScope (..))
-import Baikai.Kit.Install (installItem, listAvailable, uninstallItem, updateKit)
-import Baikai.Kit.Status (kitStatus)
+import Baikai.Kit.Config (KitConfig, KitScope (..), scopeLabel)
+import Baikai.Kit.Error (KitError, renderKitError)
+import Baikai.Kit.Install
+  ( OverwritePolicy (..),
+    UpdateReport,
+    installFrom,
+    loadManifest,
+    renderAvailable,
+    renderUninstallReport,
+    uninstallItem,
+    updateKit,
+  )
+import Baikai.Kit.Manifest (itemKind, itemName)
+import Baikai.Kit.Repo (KitRepo, RepoRefresh (..), ensureKitRepo)
+import Baikai.Kit.Status (StatusReport, UpstreamAvailability (..), kitStatus, renderStatusTable)
 import Baikai.Prelude
+import Data.Text qualified as Text
+import Data.Text.IO qualified as Text.IO
 import Options.Applicative
+import System.Exit (ExitCode (ExitFailure), exitWith)
+import System.IO (stderr)
 
 data KitCommand
   = KitList
   | KitInstall !Text !KitScope
-  | KitUpdate !(Maybe Text)
+  | KitUpdate !(Maybe Text) !OverwritePolicy
   | KitUninstall !Text !KitScope
   | KitStatus
   deriving stock (Show)
@@ -30,14 +52,106 @@
     )
     <|> pure KitList
 
+-- | Run one verb and print its normal output. Never exits, so a consumer
+--   that wants its own exit codes can map the 'KitError' itself.
+runKitCommand :: KitConfig -> KitCommand -> IO (Either KitError ())
+runKitCommand config = \case
+  KitList -> withRepo $ \repo ->
+    loadManifest (repo ^. #dir) `thenE` \manifest ->
+      printed (renderAvailable manifest)
+  KitInstall n scope -> withRepo $ \repo ->
+    loadManifest (repo ^. #dir) `thenE` \manifest ->
+      installFrom config (repo ^. #dir) manifest n scope `thenE` \item ->
+        printed $
+          "Installed " <> itemKind item <> " '" <> itemName item <> "' to " <> scopeLabel scope <> " scope."
+  KitUpdate n policy ->
+    updateKit config n policy `thenE` (printed . renderUpdateReport)
+  KitUninstall n scope ->
+    uninstallItem config n scope `thenE` (printed . renderUninstallReport n scope)
+  KitStatus -> do
+    report <- kitStatus config
+    noteUpstream report
+    Text.IO.putStrLn (renderStatusTable (report ^. #rows))
+    pure (Right ())
+  where
+    -- List and install need the manifest, so a repository they cannot
+    -- reach is an error; a stale cache is a warning and the work goes on.
+    withRepo :: (KitRepo -> IO (Either KitError ())) -> IO (Either KitError ())
+    withRepo next = do
+      repo <- ensureKitRepo config
+      case repo of
+        Left err -> pure (Left err)
+        Right resolved -> do
+          case resolved ^. #refresh of
+            RepoStale err ->
+              Text.IO.hPutStrLn stderr $
+                "Warning: kit repository could not be refreshed (" <> Text.strip err <> "); using the cached copy."
+            RepoCloned -> Text.IO.putStrLn ("Fetched " <> (config ^. #toolName) <> "-kit.")
+            RepoPulled -> pure ()
+          next resolved
+
+    noteUpstream :: StatusReport -> IO ()
+    noteUpstream report = case report ^. #upstream of
+      UpstreamReady -> pure ()
+      UpstreamStale err ->
+        Text.IO.hPutStrLn stderr $
+          "Warning: kit repository could not be refreshed ("
+            <> Text.strip err
+            <> "); comparing against the cached copy."
+      UpstreamUnavailable err ->
+        Text.IO.hPutStrLn stderr $
+          "Note: kit repository unavailable ("
+            <> Text.strip (renderKitError err)
+            <> "); showing installed items without upstream comparison."
+
+    thenE :: IO (Either KitError a) -> (a -> IO (Either KitError b)) -> IO (Either KitError b)
+    thenE step next = step >>= either (pure . Left) next
+
+    printed :: Text -> IO (Either KitError ())
+    printed message = Right <$> Text.IO.putStrLn message
+
+-- | The command adapter: 'runKitCommand', then on 'Left' print
+--   @Error: \<renderKitError e\>@ to stderr and exit 1. This is the only
+--   function in @baikai-kit@ that exits the process.
 runKit :: KitConfig -> KitCommand -> IO ()
-runKit config = \case
-  KitList -> listAvailable config
-  KitInstall n scope -> installItem config n scope
-  KitUpdate n -> updateKit config n
-  KitUninstall n scope -> uninstallItem config n scope
-  KitStatus -> kitStatus config
+runKit config kitCommand = do
+  result <- runKitCommand config kitCommand
+  case result of
+    Right () -> pure ()
+    Left err -> do
+      Text.IO.hPutStrLn stderr ("Error: " <> renderKitError err)
+      exitWith (ExitFailure 1)
 
+renderUpdateReport :: UpdateReport -> Text
+renderUpdateReport report =
+  Text.intercalate "\n" (headline ++ updatedLines ++ skippedLines ++ [summary] ++ skipSummary)
+  where
+    headline = case report ^. #refresh of
+      Nothing -> []
+      Just RepoCloned -> ["Kit repository cloned."]
+      Just RepoPulled -> ["Kit repository updated."]
+      Just (RepoStale _) -> ["Kit repository updated."]
+    updatedLines =
+      [ "Updated '" <> n <> "' (" <> scopeLabel scope <> ")"
+      | (n, scope) <- report ^. #updated
+      ]
+    -- A skip is not a failure: the command still exits 0, and the line
+    -- says exactly which invocation would overwrite the edits.
+    skippedLines =
+      [ "Skipped '"
+          <> n
+          <> "' ("
+          <> scopeLabel scope
+          <> "): installed files were modified locally; run 'kit update "
+          <> n
+          <> " --force' to overwrite."
+      | (n, scope) <- report ^. #skipped
+      ]
+    summary = "Updated " <> Text.pack (show (length (report ^. #updated))) <> " item(s)."
+    skipSummary
+      | null (report ^. #skipped) = []
+      | otherwise = ["Skipped " <> Text.pack (show (length (report ^. #skipped))) <> " item(s)."]
+
 installParser :: Parser KitCommand
 installParser =
   KitInstall
@@ -48,6 +162,10 @@
 updateParser =
   KitUpdate
     <$> optional (strArgument (metavar "NAME" <> help "Name of a specific item to update (default: all)"))
+    <*> flag
+      KeepLocalEdits
+      OverwriteLocalEdits
+      (long "force" <> help "Reinstall items even if their installed files were modified locally")
 
 uninstallParser :: Parser KitCommand
 uninstallParser =
diff --git a/src/Baikai/Kit/Error.hs b/src/Baikai/Kit/Error.hs
new file mode 100644
--- /dev/null
+++ b/src/Baikai/Kit/Error.hs
@@ -0,0 +1,102 @@
+-- | Every way a kit operation can fail.
+--
+--   Library functions return these; only 'Baikai.Kit.Command.runKit'
+--   turns one into a process exit. The 'Exception' instance exists for a
+--   caller who prefers exceptions and can write @either throwIO pure@.
+module Baikai.Kit.Error
+  ( KitError (..),
+    renderKitError,
+  )
+where
+
+import Baikai.Prelude
+import Control.Exception (Exception)
+import Data.Text qualified as Text
+
+-- | A kit operation's failure. Constructors are positional because
+--   @-Wpartial-fields@ is on and a record sum would warn.
+data KitError
+  = -- | The kit checkout holds no @kit.json@.
+    KitManifestMissing FilePath
+  | -- | The manifest did not decode; the 'Text' is aeson's message.
+    KitManifestInvalid FilePath Text
+  | -- | The manifest declares a @version@ this installer does not support.
+    KitManifestVersionUnsupported FilePath Int
+  | -- | No skill or agent of that name is listed.
+    KitItemNotFound Text
+  | -- | The item lists no source files.
+    KitItemHasNoFiles Text
+  | -- | An item name failed 'Baikai.Kit.Path.safeItemName'; the second
+    --   'Text' is that function's reason.
+    KitUnsafeName Text Text
+  | -- | A manifest path failed 'Baikai.Kit.Path.safeRelativePath'.
+    KitUnsafePath Text Text
+  | -- | A listed source file is not there.
+    KitSourceMissing FilePath
+  | -- | A component of a listed source path is a symbolic link. A kit is
+    --   plain files; see 'Baikai.Kit.Path.safeSourcePath'.
+    KitSourceSymlink FilePath
+  | -- | The canonical source path (first field) is not below the
+    --   canonical kit checkout (second field).
+    KitSourceEscapes FilePath FilePath
+  | -- | Inspecting or reading a source raised an 'IOException'.
+    KitSourceUnreadable FilePath Text
+  | -- | A first clone failed and no usable cache exists: the repository
+    --   URL and git's output.
+    KitCloneFailed Text Text
+  | -- | @git pull@ failed during @kit update@.
+    KitPullFailed Text
+  | -- | An install could not be completed: the reason, the destinations
+    --   restored by rollback, and the destinations left inconsistent.
+    --   Both lists are empty when nothing was changed.
+    KitWriteFailed Text [FilePath] [FilePath]
+  deriving stock (Eq, Show)
+  deriving anyclass (Exception)
+
+-- | The message a command adapter prints. One line, except where a
+--   failure needs to say what it left behind.
+renderKitError :: KitError -> Text
+renderKitError = \case
+  KitManifestMissing path ->
+    "kit.json not found in kit repository (" <> Text.pack path <> ")."
+  KitManifestInvalid path reason ->
+    "failed to parse " <> Text.pack path <> ": " <> reason
+  -- The supported versions are spelled out rather than read from
+  -- 'Baikai.Kit.Manifest.supportedManifestVersions': Manifest imports
+  -- this module, so the dependency cannot run the other way.
+  KitManifestVersionUnsupported path n ->
+    Text.pack path
+      <> " declares manifest version "
+      <> Text.pack (show n)
+      <> "; this installer supports versions 1 and 2."
+  KitItemNotFound n -> "'" <> n <> "' not found in kit manifest."
+  KitItemHasNoFiles n -> "'" <> n <> "' lists no source files."
+  KitUnsafeName raw reason -> "unsafe item name '" <> raw <> "': " <> reason
+  KitUnsafePath raw reason -> "unsafe manifest path '" <> raw <> "': " <> reason
+  KitSourceMissing path -> "source file does not exist: " <> Text.pack path
+  KitSourceSymlink path -> "refusing symbolic link in kit source: " <> Text.pack path
+  KitSourceEscapes path root ->
+    "kit source resolves outside the kit checkout: "
+      <> Text.pack path
+      <> " (checkout: "
+      <> Text.pack root
+      <> ")"
+  KitSourceUnreadable path reason ->
+    "cannot inspect kit source " <> Text.pack path <> ": " <> reason
+  KitCloneFailed url output ->
+    "failed to fetch kit repository " <> url <> ": " <> output
+  KitPullFailed output ->
+    "failed to update kit repository: "
+      <> output
+      <> "\nThe cached copy is unchanged; installed items were not reinstalled."
+  KitWriteFailed reason restored leftInconsistent ->
+    Text.intercalate "\n" ("install failed: " <> reason : aftermath)
+    where
+      aftermath
+        | null restored && null leftInconsistent = ["No changes were made."]
+        | otherwise =
+            ["Restored: " <> renderPaths restored | not (null restored)]
+              <> [ "Left inconsistent (repair by reinstalling): " <> renderPaths leftInconsistent
+                 | not (null leftInconsistent)
+                 ]
+      renderPaths = Text.intercalate ", " . map Text.pack
diff --git a/src/Baikai/Kit/Install.hs b/src/Baikai/Kit/Install.hs
--- a/src/Baikai/Kit/Install.hs
+++ b/src/Baikai/Kit/Install.hs
@@ -1,14 +1,29 @@
+-- | Reading the manifest and installing what it lists.
+--
+--   Every function here returns @'Either' 'KitError' a@ and prints
+--   nothing: rendering and exiting belong to 'Baikai.Kit.Command.runKit'.
+--   Internally the module raises 'KitError' and catches it at each
+--   exported boundary, which keeps the plumbing readable without changing
+--   what a caller observes.
 module Baikai.Kit.Install
   ( loadManifest,
     loadManifestMaybe,
     lookupItem,
     installItem,
+    installFrom,
     uninstallItem,
-    uninstallOutcomes,
     renderUninstallReport,
     RemovalOutcome (..),
+    OverwritePolicy (..),
+    UpdateReport (..),
     updateKit,
+    reinstallPresent,
     listAvailable,
+    renderAvailable,
+    PlannedWrite (..),
+    WriteContent (..),
+    executePlan,
+    executePlanWith,
     stripYamlFrontmatter,
   )
 where
@@ -21,27 +36,31 @@
   )
 import Baikai.Interactive (InteractiveProvider (..), InteractiveScope (InteractiveProjectScope))
 import Baikai.Kit.Config (KitConfig, KitScope (..), kitCacheDir, providerAgentsBase, providerLabel, scopeLabel, sidecarFileName)
+import Baikai.Kit.Error (KitError (..))
 import Baikai.Kit.Manifest
   ( AgentEntry,
+    ItemSources,
     KitItem (..),
     KitItemKind (..),
     KitManifest (..),
     SkillEntry,
-    itemKind,
+    itemName,
+    itemSources,
     kitItemKind,
+    supportedManifestVersions,
   )
-import Baikai.Kit.Path (safeItemName, safeRelativePath)
-import Baikai.Kit.Repo (PullResult (..), ensureKitRepo, pullKitRepo)
-import Baikai.Kit.Sidecar (computeKitHash, newSidecarMeta, sidecarPath)
+import Baikai.Kit.Path (safeItemName, safeSourcePath)
+import Baikai.Kit.Repo (KitRepo, PullResult (..), RepoRefresh (..), ensureKitRepo, pullKitRepo)
+import Baikai.Kit.Sidecar (hashEntries, newSidecarMeta, readSidecar, sidecarPath)
 import Baikai.Prelude
-import Control.Exception (IOException, catch, throwIO, try)
+import Control.Exception (IOException, onException, throwIO, try)
 import Control.Monad (forM, forM_, unless, when)
 import Data.Aeson (eitherDecodeFileStrict', encode)
+import Data.ByteString qualified as BS
 import Data.ByteString.Lazy qualified as LBS
 import Data.List (find, nub)
 import Data.Text qualified as Text
 import Data.Text.Encoding qualified as Text.Encoding
-import Data.Text.IO qualified as Text.IO
 import System.Directory
   ( createDirectoryIfMissing,
     doesDirectoryExist,
@@ -50,18 +69,21 @@
     removeFile,
     renameFile,
   )
-import System.Exit (exitFailure)
 import System.FilePath (takeDirectory, takeFileName, (</>))
-import System.IO (hPutStrLn, stderr)
+import System.IO (hClose, openTempFile)
 
+-- | One file this install will put in place. Exposed as a test seam
+--   together with 'executePlanWith'; not part of the stable surface.
 data PlannedWrite = PlannedWrite
   { destination :: !FilePath,
     content :: !WriteContent
   }
+  deriving stock (Generic, Show)
 
 data WriteContent
   = CopyFrom !FilePath
   | WriteBytes !LBS.ByteString
+  deriving stock (Show)
 
 data RemovalOutcome = RemovalOutcome
   { provider :: !InteractiveProvider,
@@ -71,73 +93,77 @@
   }
   deriving stock (Eq, Generic, Show)
 
-loadManifest :: FilePath -> IO KitManifest
-loadManifest repoDir = do
-  let manifestPath = repoDir </> "kit.json"
-  exists <- doesFileExist manifestPath
-  unless exists $ do
-    hPutStrLn stderr "Error: kit.json not found in kit repository."
-    exitFailure
-  result <- eitherDecodeFileStrict' manifestPath
-  case result of
-    Left err -> do
-      hPutStrLn stderr $ "Error: Failed to parse kit.json: " <> err
-      exitFailure
-    Right manifest -> pure manifest
+-- | What @kit update@ should do with an item whose installed files were
+--   edited after they were installed.
+data OverwritePolicy
+  = KeepLocalEdits
+  | OverwriteLocalEdits
+  deriving stock (Eq, Show)
 
-loadManifestMaybe :: FilePath -> IO (Maybe KitManifest)
-loadManifestMaybe "" = pure Nothing
-loadManifestMaybe cacheDir = do
-  let manifestPath = cacheDir </> "kit.json"
-  exists <- doesFileExist manifestPath
-  if not exists
-    then pure Nothing
-    else do
-      result <- eitherDecodeFileStrict' manifestPath
-      case result of
-        Left err -> do
-          hPutStrLn stderr $ "Warning: failed to parse kit.json: " <> err
-          pure Nothing
-        Right manifest -> pure (Just manifest)
+-- | What @kit update@ did, for the caller to render. @refresh@ is
+--   'Nothing' when no refresh was attempted, which is what
+--   'reinstallPresent' reports.
+data UpdateReport = UpdateReport
+  { refresh :: !(Maybe RepoRefresh),
+    updated :: ![(Text, KitScope)],
+    skipped :: ![(Text, KitScope)]
+  }
+  deriving stock (Eq, Generic, Show)
 
+-- | Read and validate the manifest at @<dir>/kit.json@.
+loadManifest :: FilePath -> IO (Either KitError KitManifest)
+loadManifest = kitTry . loadManifestIO
+
+-- | The same, tolerating an absent cache or an absent manifest. A
+--   manifest that is present but unreadable is still a 'Left'.
+loadManifestMaybe :: FilePath -> IO (Either KitError (Maybe KitManifest))
+loadManifestMaybe "" = pure (Right Nothing)
+loadManifestMaybe cacheDir = kitTry $ do
+  exists <- doesFileExist (cacheDir </> "kit.json")
+  if exists then Just <$> loadManifestIO cacheDir else pure Nothing
+
 lookupItem :: Text -> KitManifest -> Maybe KitItem
 lookupItem n manifest =
   case find (\entry -> entry ^. #name == n) (manifest ^. #skills) of
     Just skill -> Just (KitSkillItem skill)
     Nothing -> KitAgentItem <$> find (\entry -> entry ^. #name == n) (manifest ^. #agents)
 
-installItem :: KitConfig -> Text -> KitScope -> IO ()
-installItem config itemN scope = do
-  repoDir <- ensureKitRepo config
-  manifest <- loadManifest repoDir
-  case lookupItem itemN manifest of
-    Nothing -> do
-      hPutStrLn stderr $ "Error: '" <> Text.unpack itemN <> "' not found in kit manifest."
-      exitFailure
-    Just item -> do
-      result <- try @IOException (doInstall config repoDir item scope)
-      case result of
-        Right () ->
-          Text.IO.putStrLn $
-            "Installed " <> itemKind item <> " '" <> itemN <> "' to " <> scopeLabel scope <> " scope."
-        Left e -> do
-          hPutStrLn stderr $ "Error: install failed, no changes were made: " <> show e
-          exitFailure
+-- | Refresh the cache, read the manifest and install one item. The
+--   'KitRepo'\'s refresh state is dropped by this convenience; a command
+--   that wants to warn about a stale cache composes 'ensureKitRepo',
+--   'loadManifest' and 'installFrom' itself.
+installItem :: KitConfig -> Text -> KitScope -> IO (Either KitError KitItem)
+installItem config itemN scope = kitTry $ do
+  repo <- requireRepo config
+  manifest <- loadManifestIO (repo ^. #dir)
+  installFromIO config (repo ^. #dir) manifest itemN scope
 
-uninstallItem :: KitConfig -> Text -> KitScope -> IO ()
-uninstallItem config n scope = do
-  outcomes <- uninstallOutcomes config n scope
-  Text.IO.putStrLn (renderUninstallReport n scope outcomes)
+-- | The network-free half of 'installItem': install one item from a
+--   manifest already read out of @repoDir@.
+installFrom :: KitConfig -> FilePath -> KitManifest -> Text -> KitScope -> IO (Either KitError KitItem)
+installFrom config repoDir manifest itemN scope =
+  kitTry (installFromIO config repoDir manifest itemN scope)
 
-uninstallOutcomes :: KitConfig -> Text -> KitScope -> IO [RemovalOutcome]
-uninstallOutcomes config n scope = do
-  safeName <- requireSafe "item name" (safeItemName n)
+-- | Remove an item's assets, its resource directory and its sidecar from
+--   every provider at one scope.
+uninstallItem :: KitConfig -> Text -> KitScope -> IO (Either KitError [RemovalOutcome])
+uninstallItem config n scope = kitTry $ do
+  safeName <- orThrow (KitUnsafeName n) (safeItemName n)
   forM (config ^. #providers) $ \provider -> do
     providerBase <- providerAgentsBase config provider scope
     skillRemoved <- removeIfDirectory (skillTarget config provider providerBase safeName)
-    agentRemoved <- removeIfFile (agentTarget config provider providerBase safeName)
+    agentFileRemoved <- removeIfFile (agentTarget config provider providerBase safeName)
+    -- A multi-file agent owns a directory beside its agent file; it is
+    -- part of the agent, not a kind of its own.
+    agentDirRemoved <- removeIfDirectory (agentResourceDir config provider providerBase safeName)
     sidecarRemoved <- removeIfFile (agentSidecarTarget config provider providerBase safeName)
-    pure RemovalOutcome {provider, skillRemoved, agentRemoved, sidecarRemoved}
+    pure
+      RemovalOutcome
+        { provider,
+          skillRemoved,
+          agentRemoved = agentFileRemoved || agentDirRemoved,
+          sidecarRemoved
+        }
 
 renderUninstallReport :: Text -> KitScope -> [RemovalOutcome] -> Text
 renderUninstallReport n scope outcomes
@@ -163,200 +189,377 @@
           ++ ["agent" | any (^. #agentRemoved) outcomes]
     removedProviders = map (providerLabel . view #provider) (filter assetRemoved outcomes)
 
-updateKit :: KitConfig -> Maybe Text -> IO ()
-updateKit config mName = do
+-- | Refresh the cache and reinstall the items that are already installed.
+--   A failed refresh is an error here, unlike the other verbs: fetching
+--   is what update is for.
+updateKit :: KitConfig -> Maybe Text -> OverwritePolicy -> IO (Either KitError UpdateReport)
+updateKit config mName policy = kitTry $ do
   cacheDir <- kitCacheDir config
-  exists <- doesDirectoryExist cacheDir
-  if exists
-    then do
-      result <- pullKitRepo config cacheDir
+  isCheckout <- doesDirectoryExist (cacheDir </> ".git")
+  refreshed <-
+    if isCheckout
+      then do
+        result <- pullKitRepo config cacheDir
+        case result of
+          PullSucceeded -> pure RepoPulled
+          PullFailed err -> throwIO (KitPullFailed err)
+      else do
+        repo <- requireRepo config
+        case repo ^. #refresh of
+          RepoStale err -> throwIO (KitCloneFailed (config ^. #repoUrl) err)
+          fresh -> pure fresh
+  manifest <- loadManifestIO cacheDir
+  report <- reinstallPresentIO config cacheDir manifest mName policy
+  pure (report & #refresh .~ Just refreshed)
+
+-- | The network-free second half of 'updateKit': reinstall what is
+--   already installed from a manifest already read out of @repoDir@.
+--
+--   Under 'KeepLocalEdits' an item whose installed files no longer hash
+--   to what its sidecar recorded is skipped rather than overwritten. A
+--   sidecar written before those fields existed carries no hash, so such
+--   an item is reinstalled without the check.
+reinstallPresent ::
+  KitConfig ->
+  FilePath ->
+  KitManifest ->
+  Maybe Text ->
+  OverwritePolicy ->
+  IO (Either KitError UpdateReport)
+reinstallPresent config repoDir manifest mName policy =
+  kitTry (reinstallPresentIO config repoDir manifest mName policy)
+
+-- | Refresh the cache and read the manifest of what the kit offers.
+listAvailable :: KitConfig -> IO (Either KitError KitManifest)
+listAvailable config = kitTry $ do
+  repo <- requireRepo config
+  loadManifestIO (repo ^. #dir)
+
+-- | The listing @kit list@ prints, without a trailing newline.
+renderAvailable :: KitManifest -> Text
+renderAvailable manifest
+  | null skills && null agents = "No items available in the kit."
+  | otherwise = Text.intercalate "\n" (skillBlock ++ gap ++ agentBlock)
+  where
+    skills = manifest ^. #skills
+    agents = manifest ^. #agents
+    gap = ["" | not (null skills), not (null agents)]
+    skillBlock
+      | null skills = []
+      | otherwise = "Skills:" : map (entryLine (columnWidth (map (view #name) skills)) . skillNameDesc) skills
+    agentBlock
+      | null agents = []
+      | otherwise = "Agents:" : map (entryLine (columnWidth (map (view #name) agents)) . agentNameDesc) agents
+    columnWidth names = maximum (map Text.length names)
+    entryLine width (n, desc) = "  " <> Text.justifyLeft (width + 2) ' ' n <> desc
+
+-- | Put a plan in place, or leave the filesystem as it was.
+--
+--   Phase one writes every payload to a uniquely named temporary file in
+--   its destination's directory. Phase two, per entry, moves an existing
+--   destination aside to a unique backup and renames the temporary into
+--   place, journalling both; a failure restores every completed entry in
+--   reverse, removes the remaining temporaries and reports which paths
+--   were restored and which could not be. Same-directory renames are
+--   atomic on POSIX, so a reader sees either the old file or the new one.
+executePlan :: [PlannedWrite] -> IO (Either KitError ())
+executePlan = executePlanWith renameFile
+
+-- | 'executePlan' with an injectable rename step. A test seam; not part
+--   of the stable surface.
+executePlanWith :: (FilePath -> FilePath -> IO ()) -> [PlannedWrite] -> IO (Either KitError ())
+executePlanWith renameInto writes = do
+  clash <- firstDirectoryDestination writes
+  case clash of
+    Just dest -> pure (Left (writeFailed ("destination is a directory: " <> Text.pack dest)))
+    Nothing -> do
+      staged <- stage [] writes
+      case staged of
+        Left err -> pure (Left err)
+        Right temps -> commit [] temps
+  where
+    writeFailed reason = KitWriteFailed reason [] []
+
+    firstDirectoryDestination [] = pure Nothing
+    firstDirectoryDestination (planned : rest) = do
+      let dest = planned ^. #destination
+      isDir <- doesDirectoryExist dest
+      if isDir then pure (Just dest) else firstDirectoryDestination rest
+
+    -- Phase one. Nothing observable has changed while this runs, so a
+    -- failure removes the temporaries and reports no changes.
+    stage staged [] = pure (Right (reverse staged))
+    stage staged (planned : rest) = do
+      result <- try @IOException (stageOne planned)
       case result of
-        PullSucceeded -> Text.IO.putStrLn "Kit repository updated."
-        PullFailed err -> do
-          hPutStrLn stderr $ "Error: failed to update kit repository: " <> Text.unpack err
-          hPutStrLn stderr "The cached copy is unchanged; installed items were not reinstalled."
-          exitFailure
-    else do
-      _ <- ensureKitRepo config
-      Text.IO.putStrLn "Kit repository cloned."
-  manifest <- loadManifest =<< kitCacheDir config
-  case mName of
-    Just n -> do
-      reinstallIfPresent config n UserScope manifest
-      reinstallIfPresent config n ProjectScope manifest
-    Nothing -> reinstallAllPresent config manifest
+        Left e -> do
+          removeTemps staged
+          pure (Left (writeFailed (Text.pack (show e))))
+        Right pair -> stage (pair : staged) rest
 
-listAvailable :: KitConfig -> IO ()
-listAvailable config = do
-  repoDir <- ensureKitRepo config
-  manifest <- loadManifest repoDir
-  let sk = manifest ^. #skills
-      ag = manifest ^. #agents
-  if null sk && null ag
-    then Text.IO.putStrLn "No items available in the kit."
-    else do
-      unless (null sk) $ do
-        Text.IO.putStrLn "Skills:"
-        let maxLen = maximum $ map (Text.length . view #name) sk
-        mapM_ (printEntry maxLen . skillNameDesc) sk
-      unless (null ag) $ do
-        unless (null sk) (Text.IO.putStrLn "")
-        Text.IO.putStrLn "Agents:"
-        let maxLen = maximum $ map (Text.length . view #name) ag
-        mapM_ (printEntry maxLen . agentNameDesc) ag
+    stageOne planned = do
+      let dest = planned ^. #destination
+          dir = takeDirectory dest
+      bytes <- payload (planned ^. #content)
+      createDirectoryIfMissing True dir
+      -- 'openTempFile' splits the template at its last extension, so the
+      -- file is named <dest><random>.baikai-kit-tmp: unique, and still
+      -- carrying the suffix a residue check looks for.
+      (temp, handle) <- openTempFile dir (takeFileName dest <> ".baikai-kit-tmp")
+      (LBS.hPut handle bytes >> hClose handle)
+        `onException` (hClose handle >> ignoring (removeFile temp))
+      pure (temp, dest)
+
+    payload (CopyFrom src) = LBS.readFile src
+    payload (WriteBytes bytes) = pure bytes
+
+    -- Phase two. Every entry that changed anything is journalled with the
+    -- backup it displaced and whether its rename completed.
+    commit journal [] = do
+      forM_ journal $ \(_, mBackup, _) -> forM_ mBackup (ignoring . removeFile)
+      pure (Right ())
+    commit journal (entry@(temp, dest) : rest) = do
+      backed <- try @IOException (backupExisting dest)
+      case backed of
+        Left e -> unwind journal (entry : rest) e
+        Right mBackup -> do
+          renamed <- try @IOException (renameInto temp dest)
+          case renamed of
+            Left e -> unwind ((dest, mBackup, False) : journal) (entry : rest) e
+            Right () -> commit ((dest, mBackup, True) : journal) rest
+
+    backupExisting dest = do
+      exists <- doesFileExist dest
+      if not exists
+        then pure Nothing
+        else do
+          (backup, handle) <- openTempFile (takeDirectory dest) (takeFileName dest <> ".baikai-kit-bak")
+          hClose handle
+          renameFile dest backup
+          pure (Just backup)
+
+    unwind journal remaining e = do
+      outcomes <- forM (filter changedSomething journal) $ \(dest, mBackup, renamed) -> do
+        restored <- try @IOException (restoreEntry dest mBackup renamed)
+        pure (dest, either (const False) (const True) (restored :: Either IOException ()))
+      removeTemps remaining
+      pure . Left $
+        KitWriteFailed
+          (Text.pack (show e))
+          [dest | (dest, True) <- outcomes]
+          [dest | (dest, False) <- outcomes]
+
+    changedSomething (_, mBackup, renamed) = renamed || has _Just mBackup
+
+    restoreEntry dest (Just backup) _ = renameFile backup dest
+    restoreEntry dest Nothing True = removeFile dest
+    restoreEntry _ Nothing False = pure ()
+
+    removeTemps entries = forM_ entries $ \(temp, _) -> ignoring (removeFile temp)
+
+    ignoring action = do
+      _ <- try @IOException action
+      pure ()
+
+-- Internal ------------------------------------------------------------
+
+loadManifestIO :: FilePath -> IO KitManifest
+loadManifestIO repoDir = do
+  let manifestPath = repoDir </> "kit.json"
+  exists <- doesFileExist manifestPath
+  unless exists (throwIO (KitManifestMissing manifestPath))
+  result <- eitherDecodeFileStrict' manifestPath
+  case result of
+    Left err -> throwIO (KitManifestInvalid manifestPath (Text.pack err))
+    Right manifest -> do
+      let declared = manifest ^. #version
+      unless (declared `elem` supportedManifestVersions) $
+        throwIO (KitManifestVersionUnsupported manifestPath declared)
+      pure manifest
+
+installFromIO :: KitConfig -> FilePath -> KitManifest -> Text -> KitScope -> IO KitItem
+installFromIO config repoDir manifest itemN scope =
+  case lookupItem itemN manifest of
+    Nothing -> throwIO (KitItemNotFound itemN)
+    Just item -> do
+      doInstall config repoDir item scope
+      pure item
+
+requireRepo :: KitConfig -> IO KitRepo
+requireRepo config = ensureKitRepo config >>= either throwIO pure
+
+reinstallPresentIO ::
+  KitConfig ->
+  FilePath ->
+  KitManifest ->
+  Maybe Text ->
+  OverwritePolicy ->
+  IO UpdateReport
+reinstallPresentIO config repoDir manifest mName policy = do
+  results <-
+    fmap concat . forM candidates $ \n ->
+      fmap concat . forM [UserScope, ProjectScope] $ \scope -> do
+        installed <- isInstalled config n scope
+        case (installed, lookupItem n manifest) of
+          (True, Just item) -> do
+            modified <- case policy of
+              OverwriteLocalEdits -> pure False
+              KeepLocalEdits -> locallyModified config item scope
+            if modified
+              then pure [Left (n, scope)]
+              else do
+                doInstall config repoDir item scope
+                pure [Right (n, scope)]
+          _ -> pure []
+  pure
+    UpdateReport
+      { refresh = Nothing,
+        updated = [entry | Right entry <- results],
+        skipped = [entry | Left entry <- results]
+      }
   where
-    printEntry maxLen (n, desc) =
-      Text.IO.putStrLn $ "  " <> Text.justifyLeft (maxLen + 2) ' ' n <> desc
+    candidates = case mName of
+      Just n -> [n]
+      Nothing ->
+        map (view #name) (manifest ^. #skills)
+          ++ map (view #name) (manifest ^. #agents)
 
+-- | Do this item's installed files still hash to what its sidecar
+--   recorded? A file that cannot be read counts as modified; a sidecar
+--   without the recorded names and hash is not checked.
+locallyModified :: KitConfig -> KitItem -> KitScope -> IO Bool
+locallyModified config item scope = do
+  safeName <- orThrow (KitUnsafeName (itemName item)) (safeItemName (itemName item))
+  checks <- forM (config ^. #providers) $ \provider -> do
+    providerBase <- providerAgentsBase config provider scope
+    let kind = kitItemKind item
+        root = installedRoot config provider providerBase kind safeName
+    mSidecar <- readSidecar (sidecarPath provider kind (Text.pack safeName) providerBase (sidecarFileName config))
+    case mSidecar of
+      Nothing -> pure False
+      Just sidecar ->
+        case (sidecar ^. #installedFiles, sidecar ^. #installedHash) of
+          (Just recorded, Just expected) -> do
+            entries <- forM recorded $ \rel -> do
+              bytes <- try @IOException (BS.readFile (root </> Text.unpack rel))
+              pure (either (const Nothing) (Just . (Text.unpack rel,)) (bytes :: Either IOException BS.ByteString))
+            pure $ case sequence entries of
+              Nothing -> True
+              Just pairs -> hashEntries pairs /= expected
+          _ -> pure False
+  pure (or checks)
+
 doInstall :: KitConfig -> FilePath -> KitItem -> KitScope -> IO ()
-doInstall config repoDir item scope =
-  planInstall config repoDir item scope >>= executePlan
+doInstall config repoDir item scope = do
+  writes <- planInstall config repoDir item scope
+  executePlan writes >>= either throwIO pure
 
+-- | One installed asset: its name relative to the provider's installed
+--   root, where it goes, and the bytes to put there.
+data PlannedAsset = PlannedAsset
+  { relativeName :: !FilePath,
+    target :: !FilePath,
+    bytes :: !LBS.ByteString
+  }
+  deriving stock (Generic)
+
 planInstall :: KitConfig -> FilePath -> KitItem -> KitScope -> IO [PlannedWrite]
-planInstall config repoDir item@(KitSkillItem entry) scope = do
-  safeName <- requireSafe "skill name" (safeItemName (entry ^. #name))
-  safePath <- requireSafe "skill path" (safeRelativePath (entry ^. #path))
-  safeFiles <- traverse (requireSafe "skill file" . safeRelativePath) (entry ^. #files)
-  let sourceDir = repoDir </> safePath
-  forM_ safeFiles $ \file -> requireSourceFile (sourceDir </> file)
-  hashStr <- computeKitHash sourceDir (map Text.pack safeFiles)
-  meta <- newSidecarMeta item hashStr
+planInstall config repoDir item scope = do
+  safeName <- orThrow (KitUnsafeName (itemName item)) (safeItemName (itemName item))
+  sources <- either throwIO pure (itemSources item)
+  resolved <- resolveSources repoDir sources
+  contents <- forM resolved $ \(rel, path) -> do
+    read' <- try @IOException (BS.readFile path)
+    case read' of
+      Left e -> throwIO (KitSourceUnreadable path (Text.pack (show e)))
+      Right raw -> pure (rel, path, raw)
+  let upstreamHash = hashEntries [(rel, raw) | (rel, _, raw) <- contents]
   fmap concat $
     forM (config ^. #providers) $ \provider -> do
       targetBase <- providerAgentsBase config provider scope
-      let targetDir = skillTarget config provider targetBase safeName
-          fileWrites =
-            [ PlannedWrite
-                { destination = targetDir </> file,
-                  content = CopyFrom (sourceDir </> file)
-                }
-            | file <- safeFiles
+      assets <- providerAssets config provider targetBase safeName item contents
+      let installedNames = [Text.pack (asset ^. #relativeName) | asset <- assets]
+          installedDigest =
+            hashEntries [(asset ^. #relativeName, LBS.toStrict (asset ^. #bytes)) | asset <- assets]
+      meta <- newSidecarMeta item upstreamHash installedNames installedDigest
+      let assetWrites =
+            [ PlannedWrite {destination = asset ^. #target, content = WriteBytes (asset ^. #bytes)}
+            | asset <- assets
             ]
           sidecarWrite =
             PlannedWrite
-              { destination = sidecarPath provider (kitItemKind item) (Text.pack safeName) targetBase (sidecarFileName config),
-                content = WriteBytes (encode meta)
-              }
-      pure (fileWrites ++ [sidecarWrite])
-planInstall config repoDir item@(KitAgentItem entry) scope = do
-  safeName <- requireSafe "agent name" (safeItemName (entry ^. #name))
-  (sourceBase, relFiles, primarySource) <- safeAgentSources repoDir entry
-  forM_ relFiles $ \file -> requireSourceFile (sourceBase </> file)
-  hashStr <- computeKitHash sourceBase (map Text.pack relFiles)
-  meta <- newSidecarMeta item hashStr
-  body <- Text.IO.readFile primarySource
-  fmap concat $
-    forM (config ^. #providers) $ \provider -> do
-      targetBase <- providerAgentsBase config provider scope
-      let dstFile = agentTarget config provider targetBase safeName
-          agentWrite =
-            case provider of
-              InteractiveClaude ->
-                PlannedWrite {destination = dstFile, content = CopyFrom primarySource}
-              InteractiveCodex ->
-                PlannedWrite
-                  { destination = dstFile,
-                    content = WriteBytes (LBS.fromStrict (Text.Encoding.encodeUtf8 (agentAsCodexToml entry body)))
-                  }
-          sidecarWrite =
-            PlannedWrite
-              { destination = sidecarPath provider (kitItemKind item) (Text.pack safeName) targetBase (sidecarFileName config),
+              { destination =
+                  sidecarPath provider (kitItemKind item) (Text.pack safeName) targetBase (sidecarFileName config),
                 content = WriteBytes (encode meta)
               }
-      pure [agentWrite, sidecarWrite]
-
-safeAgentSources :: FilePath -> AgentEntry -> IO (FilePath, [FilePath], FilePath)
-safeAgentSources repoDir entry =
-  case entry ^. #files of
-    Just files -> do
-      safePath <- requireSafe "agent path" (safeRelativePath (entry ^. #path))
-      safeFiles <- traverse (requireSafe "agent file" . safeRelativePath) files
-      case safeFiles of
-        [] -> do
-          hPutStrLn stderr $ "Error: agent '" <> Text.unpack (entry ^. #name) <> "' has no source files."
-          exitFailure
-        primaryRel : _ -> do
-          let sourceBase = repoDir </> safePath
-          pure (sourceBase, safeFiles, sourceBase </> primaryRel)
-    Nothing -> do
-      safePath <- requireSafe "agent path" (safeRelativePath (entry ^. #path))
-      let fileName = takeFileName safePath
-      pure (repoDir </> takeDirectory safePath, [fileName], repoDir </> safePath)
-
-requireSourceFile :: FilePath -> IO ()
-requireSourceFile path = do
-  exists <- doesFileExist path
-  unless exists (ioError (userError ("source file does not exist: " <> path)))
-
-executePlan :: [PlannedWrite] -> IO ()
-executePlan writes = do
-  tempPaths <- phaseOne [] writes
-  forM_ tempPaths $ \(temp, final) -> renameFile temp final
-  where
-    phaseOne temps [] = pure (reverse temps)
-    phaseOne temps (PlannedWrite {destination, content} : rest) = do
-      let temp = destination <> ".baikai-kit-tmp"
-      result <-
-        try @IOException $ do
-          createDirectoryIfMissing True (takeDirectory destination)
-          writeTemp content temp
-          pure (temp, destination)
-      case result of
-        Left e -> cleanupTemps temps >> throwIO e
-        Right tempPair ->
-          phaseOne (tempPair : temps) rest
-            `catch` \(e :: IOException) -> cleanupTemps (tempPair : temps) >> throwIO e
-
-    writeTemp (CopyFrom src) temp = LBS.readFile src >>= LBS.writeFile temp
-    writeTemp (WriteBytes bytes) temp = LBS.writeFile temp bytes
-
-    cleanupTemps temps =
-      forM_ temps $ \(temp, _) -> do
-        _ <- try @IOException (removeFile temp)
-        pure ()
+      pure (assetWrites ++ [sidecarWrite])
 
-requireSafe :: Text -> Either Text a -> IO a
-requireSafe what = \case
-  Right a -> pure a
-  Left reason -> do
-    hPutStrLn stderr $ "Error: unsafe " <> Text.unpack what <> ": " <> Text.unpack reason
-    exitFailure
+-- | Turn an item's sources into what one provider gets. A skill's files
+--   keep their names below the skill directory. An agent's first file
+--   becomes the provider's agent file — copied for Claude, rendered to
+--   TOML for Codex — and every remaining file goes into a resource
+--   directory named after the agent beside it, because both providers'
+--   agent directories are flat and a stray Markdown file there would be
+--   discovered as a bogus agent.
+providerAssets ::
+  KitConfig ->
+  InteractiveProvider ->
+  FilePath ->
+  FilePath ->
+  KitItem ->
+  [(FilePath, FilePath, BS.ByteString)] ->
+  IO [PlannedAsset]
+providerAssets config provider targetBase safeName (KitSkillItem _) contents =
+  pure
+    [ PlannedAsset
+        { relativeName = rel,
+          target = skillTarget config provider targetBase safeName </> rel,
+          bytes = LBS.fromStrict raw
+        }
+    | (rel, _, raw) <- contents
+    ]
+providerAssets config provider targetBase safeName (KitAgentItem entry) contents =
+  case contents of
+    [] -> throwIO (KitItemHasNoFiles (entry ^. #name))
+    (_, primaryPath, primaryRaw) : extras -> do
+      let agentFile = agentTarget config provider targetBase safeName
+          resourceDir = agentResourceDir config provider targetBase safeName
+      body <- decodeSource primaryPath primaryRaw
+      let primaryBytes = case provider of
+            InteractiveClaude -> LBS.fromStrict primaryRaw
+            InteractiveCodex -> LBS.fromStrict (Text.Encoding.encodeUtf8 (agentAsCodexToml entry body))
+      pure $
+        PlannedAsset
+          { relativeName = takeFileName agentFile,
+            target = agentFile,
+            bytes = primaryBytes
+          }
+          : [ PlannedAsset
+                { relativeName = safeName </> rel,
+                  target = resourceDir </> rel,
+                  bytes = LBS.fromStrict raw
+                }
+            | (rel, _, raw) <- extras
+            ]
 
-reinstallIfPresent :: KitConfig -> Text -> KitScope -> KitManifest -> IO ()
-reinstallIfPresent config n scope manifest = do
-  installed <- isInstalled config n scope
-  when installed $
-    case lookupItem n manifest of
-      Nothing -> pure ()
-      Just item -> do
-        repoDir <- kitCacheDir config
-        doInstall config repoDir item scope
-        Text.IO.putStrLn $ "Updated '" <> n <> "' (" <> scopeLabel scope <> ")"
+-- | Agent bodies are UTF-8, not whatever the locale says. (ADR 0007.)
+decodeSource :: FilePath -> BS.ByteString -> IO Text
+decodeSource path raw =
+  case Text.Encoding.decodeUtf8' raw of
+    Left err -> throwIO (KitSourceUnreadable path (Text.pack (show err)))
+    Right text -> pure text
 
-reinstallAllPresent :: KitConfig -> KitManifest -> IO ()
-reinstallAllPresent config manifest = do
-  let allNames =
-        map (view #name) (manifest ^. #skills)
-          ++ map (view #name) (manifest ^. #agents)
-  repoDir <- kitCacheDir config
-  updated <- fmap sum $ forM allNames $ \n -> do
-    userInstalled <- isInstalled config n UserScope
-    projectInstalled <- isInstalled config n ProjectScope
-    let count = (if userInstalled then 1 else 0) + (if projectInstalled then 1 else 0) :: Int
-    when userInstalled $
-      case lookupItem n manifest of
-        Nothing -> pure ()
-        Just item -> doInstall config repoDir item UserScope
-    when projectInstalled $
-      case lookupItem n manifest of
-        Nothing -> pure ()
-        Just item -> doInstall config repoDir item ProjectScope
-    pure count
-  Text.IO.putStrLn $ "Updated " <> Text.pack (show updated) <> " item(s)."
+-- | Resolve every listed file through 'safeSourcePath', pairing the name
+-- relative to the item's base with the absolute path to read.
+resolveSources :: FilePath -> ItemSources -> IO [(FilePath, FilePath)]
+resolveSources repoDir sources =
+  forM (sources ^. #files) $ \rel -> do
+    resolved <- safeSourcePath repoDir ((sources ^. #base) </> rel)
+    (rel,) <$> either throwIO pure resolved
 
 isInstalled :: KitConfig -> Text -> KitScope -> IO Bool
 isInstalled config n scope = do
-  safeName <- requireSafe "item name" (safeItemName n)
+  safeName <- orThrow (KitUnsafeName n) (safeItemName n)
   results <- forM (config ^. #providers) $ \provider -> do
     providerBase <- providerAgentsBase config provider scope
     skillExists <- doesDirectoryExist (skillTarget config provider providerBase safeName)
@@ -364,6 +567,14 @@
     pure (skillExists || agentExists)
   pure (or results)
 
+-- | Run an action that may raise a 'KitError' and hand the caller a
+--   value. Only 'KitError' is caught; anything else propagates.
+kitTry :: IO a -> IO (Either KitError a)
+kitTry = try
+
+orThrow :: (Text -> KitError) -> Either Text a -> IO a
+orThrow toError = either (throwIO . toError) pure
+
 removeIfDirectory :: FilePath -> IO Bool
 removeIfDirectory dir = do
   exists <- doesDirectoryExist dir
@@ -384,6 +595,19 @@
 agentTarget _config provider targetBase n =
   targetBase </> agentTargetPath provider InteractiveProjectScope n
 
+-- | Where a multi-file agent's extra files live: beside its agent file,
+--   in a directory named after the agent.
+agentResourceDir :: KitConfig -> InteractiveProvider -> FilePath -> FilePath -> FilePath
+agentResourceDir config provider targetBase n =
+  takeDirectory (agentTarget config provider targetBase n) </> n
+
+-- | The directory the names in a sidecar's @installedFiles@ are relative
+--   to, per provider and kind.
+installedRoot :: KitConfig -> InteractiveProvider -> FilePath -> KitItemKind -> FilePath -> FilePath
+installedRoot config provider targetBase SkillKind n = skillTarget config provider targetBase n
+installedRoot config provider targetBase AgentKind n =
+  takeDirectory (agentTarget config provider targetBase n)
+
 agentSidecarTarget :: KitConfig -> InteractiveProvider -> FilePath -> FilePath -> FilePath
 agentSidecarTarget config provider targetBase n =
   sidecarPath provider AgentKind (Text.pack n) targetBase (sidecarFileName config)
@@ -403,12 +627,17 @@
         developerInstructions = stripYamlFrontmatter body
       }
 
+-- | Drop a leading YAML frontmatter block and normalise line endings to
+--   LF. Every branch normalises, including input with no frontmatter and
+--   input whose frontmatter is never closed.
 stripYamlFrontmatter :: Text -> Text
 stripYamlFrontmatter input =
-  case map dropCr (Text.splitOn "\n" input) of
-    "---" : rest
-      | (_, _ : body) <- break (== "---") rest ->
+  case textLines of
+    firstLine : rest
+      | isDelimiter firstLine,
+        (_, _ : body) <- break isDelimiter rest ->
           Text.intercalate "\n" body
-    _ -> input
+    _ -> Text.intercalate "\n" textLines
   where
-    dropCr = Text.dropWhileEnd (== '\r')
+    textLines = map (Text.dropWhileEnd (== '\r')) (Text.splitOn "\n" input)
+    isDelimiter = (== "---") . Text.stripEnd
diff --git a/src/Baikai/Kit/Manifest.hs b/src/Baikai/Kit/Manifest.hs
--- a/src/Baikai/Kit/Manifest.hs
+++ b/src/Baikai/Kit/Manifest.hs
@@ -1,21 +1,25 @@
 module Baikai.Kit.Manifest
   ( AgentEntry (..),
+    ItemSources (..),
     KitItem (..),
     KitItemKind (..),
     KitManifest (..),
     SkillEntry (..),
-    agentSources,
     itemKind,
     itemName,
+    itemSources,
     itemVersion,
     kitItemKind,
     kindLabel,
+    supportedManifestVersions,
   )
 where
 
+import Baikai.Kit.Error (KitError (..))
+import Baikai.Kit.Path (safeItemName, safeRelativePath)
 import Baikai.Prelude
-import Data.Text qualified as Text
-import System.FilePath (takeFileName, (</>))
+import Data.Bifunctor (first)
+import System.FilePath (takeDirectory, takeFileName)
 
 data KitManifest = KitManifest
   { version :: !Int,
@@ -55,13 +59,49 @@
   | AgentKind
   deriving stock (Eq, Ord, Show)
 
-agentSources :: AgentEntry -> [(FilePath, FilePath)]
-agentSources entry =
-  case entry ^. #files of
-    Just fs -> [(Text.unpack (entry ^. #path) </> Text.unpack f, Text.unpack f) | f <- fs]
-    Nothing ->
-      let source = Text.unpack (entry ^. #path)
-       in [(source, takeFileName source)]
+-- | The manifest versions this installer understands. Both decode
+--   identically today; a future version with different semantics must be
+--   refused rather than misinstalled.
+supportedManifestVersions :: [Int]
+supportedManifestVersions = [1, 2]
+
+-- | Where an item's files live inside the kit checkout: a directory
+--   relative to the checkout and file names relative to that directory
+--   (the first is the agent body for agents).
+--
+--   Lexically validated; physical checks are
+--   'Baikai.Kit.Path.safeSourcePath'.
+data ItemSources = ItemSources
+  { base :: !FilePath,
+    files :: ![FilePath]
+  }
+  deriving stock (Eq, Generic, Show)
+
+-- | Derive an item's source list. Fails with 'KitUnsafeName',
+--   'KitUnsafePath' or 'KitItemHasNoFiles'. The item name is validated
+--   here too, so every consumer of the result has already seen it pass.
+itemSources :: KitItem -> Either KitError ItemSources
+itemSources item = do
+  _ <- first (KitUnsafeName (itemName item)) (safeItemName (itemName item))
+  case item of
+    KitSkillItem entry -> do
+      base <- lexPath (entry ^. #path)
+      files <- traverse lexPath (entry ^. #files)
+      nonEmpty ItemSources {base, files}
+    KitAgentItem entry ->
+      case entry ^. #files of
+        Just declared -> do
+          base <- lexPath (entry ^. #path)
+          files <- traverse lexPath declared
+          nonEmpty ItemSources {base, files}
+        Nothing -> do
+          source <- lexPath (entry ^. #path)
+          pure ItemSources {base = takeDirectory source, files = [takeFileName source]}
+  where
+    lexPath raw = first (KitUnsafePath raw) (safeRelativePath raw)
+    nonEmpty sources
+      | null (sources ^. #files) = Left (KitItemHasNoFiles (itemName item))
+      | otherwise = Right sources
 
 itemName :: KitItem -> Text
 itemName (KitSkillItem entry) = entry ^. #name
diff --git a/src/Baikai/Kit/Path.hs b/src/Baikai/Kit/Path.hs
--- a/src/Baikai/Kit/Path.hs
+++ b/src/Baikai/Kit/Path.hs
@@ -1,12 +1,16 @@
 module Baikai.Kit.Path
   ( safeItemName,
     safeRelativePath,
-    safeUnder,
+    safeSourcePath,
   )
 where
 
+import Baikai.Kit.Error (KitError (..))
 import Baikai.Prelude
+import Control.Exception (IOException, try)
+import Data.List (isPrefixOf)
 import Data.Text qualified as Text
+import System.Directory (canonicalizePath, doesFileExist, doesPathExist, pathIsSymbolicLink)
 import System.FilePath (isAbsolute, normalise, splitDirectories, (</>))
 
 safeRelativePath :: Text -> Either Text FilePath
@@ -36,5 +40,58 @@
       | length (splitDirectories name) /= 1 = Left "name must be a single path segment"
       | otherwise = Right name
 
-safeUnder :: FilePath -> Text -> Either Text FilePath
-safeUnder base rel = (base </>) <$> safeRelativePath rel
+-- | Resolve an untrusted relative source path below a trusted kit
+--   checkout.
+--
+--   Runs 'safeRelativePath' on the relative path, then walks every prefix
+--   of it below @root@: a prefix that does not exist is
+--   'KitSourceMissing', a prefix that is a symbolic link
+--   ('pathIsSymbolicLink') is 'KitSourceSymlink'. Finally the canonical
+--   form of the full path must lie component-wise below the canonical
+--   form of @root@ ('canonicalizePath' on both, compared with
+--   'splitDirectories'), else 'KitSourceEscapes', and the full path must
+--   be a regular file ('doesFileExist'), else 'KitSourceMissing'. Any
+--   'IOException' raised while inspecting a prefix is
+--   'KitSourceUnreadable'. Returns @root '</>' rel@.
+--
+--   Check-then-read: the caller reads the returned path afterwards; a
+--   writer to the checkout could swap a file for a link in between, which
+--   is accepted because the checkout is owned by the invoking user and
+--   written only by git before this runs.
+safeSourcePath :: FilePath -> FilePath -> IO (Either KitError FilePath)
+safeSourcePath root rel =
+  case safeRelativePath (Text.pack rel) of
+    Left reason -> pure (Left (KitUnsafePath (Text.pack rel) reason))
+    Right validated -> do
+      let full = root </> validated
+          components = filter (/= ".") (splitDirectories validated)
+      outcome <- try @IOException (inspect root full components)
+      pure (either (Left . KitSourceUnreadable full . Text.pack . show) id outcome)
+  where
+    inspect base full components = do
+      walked <- walkPrefixes base components
+      case walked of
+        Just err -> pure (Left err)
+        Nothing -> do
+          canonRoot <- canonicalizePath base
+          canonFull <- canonicalizePath full
+          if not (splitDirectories canonRoot `isPrefixOf` splitDirectories canonFull)
+            then pure (Left (KitSourceEscapes canonFull canonRoot))
+            else do
+              isFile <- doesFileExist full
+              pure (if isFile then Right full else Left (KitSourceMissing full))
+
+    walkPrefixes _ [] = pure Nothing
+    walkPrefixes base (component : rest) = do
+      let here = base </> component
+      -- 'doesPathExist' is False for a dangling link, which refuses the
+      -- path without following it; 'pathIsSymbolicLink' throws when the
+      -- path is absent, so the existence check comes first.
+      exists <- doesPathExist here
+      if not exists
+        then pure (Just (KitSourceMissing here))
+        else do
+          isLink <- pathIsSymbolicLink here
+          if isLink
+            then pure (Just (KitSourceSymlink here))
+            else walkPrefixes here rest
diff --git a/src/Baikai/Kit/Repo.hs b/src/Baikai/Kit/Repo.hs
--- a/src/Baikai/Kit/Repo.hs
+++ b/src/Baikai/Kit/Repo.hs
@@ -1,19 +1,20 @@
 module Baikai.Kit.Repo
-  ( ensureKitRepo,
+  ( KitRepo (..),
+    RepoRefresh (..),
+    ensureKitRepo,
     PullResult (..),
     pullKitRepo,
   )
 where
 
 import Baikai.Kit.Config (KitConfig, kitCacheDir)
+import Baikai.Kit.Error (KitError (..))
 import Baikai.Prelude
 import Control.Exception (IOException, try)
 import Data.Text qualified as Text
-import Data.Text.IO qualified as Text.IO
 import System.Directory (createDirectoryIfMissing, doesDirectoryExist, doesFileExist)
-import System.Exit (ExitCode (..), exitFailure)
+import System.Exit (ExitCode (..))
 import System.FilePath ((</>))
-import System.IO (hPutStrLn, stderr)
 import System.Process (readProcessWithExitCode)
 
 data PullResult
@@ -21,37 +22,58 @@
   | PullFailed !Text
   deriving stock (Eq, Show)
 
-ensureKitRepo :: KitConfig -> IO FilePath
+-- | What happened to the cache on the way to returning it.
+data RepoRefresh
+  = -- | The cache did not exist and was cloned.
+    RepoCloned
+  | -- | The cache existed and was pulled.
+    RepoPulled
+  | -- | The refresh failed and the cached copy is being used as it is;
+    --   the 'Text' is git's output. A caller that needs fresh content
+    --   (@kit update@) treats this as a failure; the others warn.
+    RepoStale !Text
+  deriving stock (Eq, Show)
+
+data KitRepo = KitRepo
+  { dir :: !FilePath,
+    refresh :: !RepoRefresh
+  }
+  deriving stock (Eq, Generic, Show)
+
+-- | Resolve the kit cache, refreshing it if it is already a checkout and
+--   cloning it if it is not. Never prints and never exits: a first clone
+--   that fails with no usable cache is 'KitCloneFailed', and a failed
+--   refresh over a usable cache is 'RepoStale'.
+ensureKitRepo :: KitConfig -> IO (Either KitError KitRepo)
 ensureKitRepo config = do
   cacheDir <- kitCacheDir config
   exists <- doesDirectoryExist (cacheDir </> ".git")
   if exists
     then do
       result <- pullKitRepo config cacheDir
-      case result of
-        PullSucceeded -> pure ()
-        PullFailed err ->
-          hPutStrLn stderr $ "Warning: git pull failed, using cached data. " <> Text.unpack err
-      pure cacheDir
+      pure . Right $ case result of
+        PullSucceeded -> KitRepo {dir = cacheDir, refresh = RepoPulled}
+        PullFailed err -> KitRepo {dir = cacheDir, refresh = RepoStale err}
     else do
-      Text.IO.putStrLn $ "Fetching " <> (config ^. #toolName) <> "-kit..."
-      createDirectoryIfMissing True cacheDir
-      (exitCode, _, errOut) <-
-        readProcessWithExitCode
-          "git"
-          ["clone", "--depth", "1", Text.unpack (config ^. #repoUrl), cacheDir]
-          ""
-      case exitCode of
-        ExitSuccess -> pure cacheDir
-        ExitFailure _ -> do
-          manifestExists <- doesFileExist (cacheDir </> "kit.json")
-          if manifestExists
-            then do
-              hPutStrLn stderr $ "Warning: git clone failed, using cached data. " <> errOut
-              pure cacheDir
-            else do
-              hPutStrLn stderr $ "Error: Failed to fetch kit repository: " <> errOut
-              exitFailure
+      cloned <-
+        try @IOException $ do
+          createDirectoryIfMissing True cacheDir
+          readProcessWithExitCode
+            "git"
+            ["clone", "--depth", "1", Text.unpack (config ^. #repoUrl), cacheDir]
+            ""
+      case cloned of
+        -- A missing `git` binary arrives here as an IOException.
+        Left e -> staleOrFailed cacheDir (Text.pack (show e))
+        Right (ExitSuccess, _, _) -> pure (Right KitRepo {dir = cacheDir, refresh = RepoCloned})
+        Right (ExitFailure _, _, errOut) -> staleOrFailed cacheDir (Text.pack errOut)
+  where
+    staleOrFailed cacheDir output = do
+      manifestExists <- doesFileExist (cacheDir </> "kit.json")
+      pure $
+        if manifestExists
+          then Right KitRepo {dir = cacheDir, refresh = RepoStale output}
+          else Left (KitCloneFailed (config ^. #repoUrl) output)
 
 pullKitRepo :: KitConfig -> FilePath -> IO PullResult
 pullKitRepo _config cacheDir = do
diff --git a/src/Baikai/Kit/Sidecar.hs b/src/Baikai/Kit/Sidecar.hs
--- a/src/Baikai/Kit/Sidecar.hs
+++ b/src/Baikai/Kit/Sidecar.hs
@@ -1,58 +1,93 @@
 module Baikai.Kit.Sidecar
   ( SidecarMeta (..),
     computeKitHash,
+    hashEntries,
     newSidecarMeta,
     sidecarPath,
     readSidecar,
-    writeSidecar,
   )
 where
 
 import Baikai.AgentAssets (AgentAssetProvider, agentTargetPath, skillTargetPath)
 import Baikai.Interactive (InteractiveScope (InteractiveProjectScope))
-import Baikai.Kit.Manifest (KitItem, KitItemKind (..), itemKind, itemName, itemVersion, kitItemKind)
-import Baikai.Kit.Path (safeRelativePath)
+import Baikai.Kit.Error (KitError (..))
+import Baikai.Kit.Manifest (KitItem, KitItemKind (..), itemKind, itemName, itemVersion)
+import Baikai.Kit.Path (safeSourcePath)
 import Baikai.Prelude
+import Control.Exception (IOException, try)
 import Crypto.Hash (Digest, SHA256)
 import Crypto.Hash qualified as Hash
-import Data.Aeson (eitherDecodeFileStrict', encode)
+import Data.Aeson (eitherDecodeFileStrict')
 import Data.Binary.Put (putWord64be, runPut)
 import Data.ByteString qualified as BS
 import Data.ByteString.Lazy qualified as LBS
-import Data.List (sort)
+import Data.List (sortOn)
 import Data.Text qualified as Text
 import Data.Text.Encoding qualified as Text.Encoding
 import Data.Time.Clock (getCurrentTime)
 import Data.Time.Format (defaultTimeLocale, formatTime)
-import System.Directory (createDirectoryIfMissing, doesFileExist)
-import System.FilePath (dropExtension, takeDirectory, (</>))
+import System.Directory (doesFileExist)
+import System.FilePath (dropExtension, (</>))
 import System.IO (hPutStrLn, stderr)
 
+-- | The metadata written beside each installed asset.
+--
+--   @installedFiles@ and @installedHash@ describe what this tool wrote
+--   for one provider — the file names relative to that provider's target
+--   directory, and the hash of exactly those bytes — so @kit update@ can
+--   tell a file the user edited from one it installed. Both are 'Nothing'
+--   in sidecars written before those fields existed, and such an item is
+--   updated without the check.
 data SidecarMeta = SidecarMeta
   { name :: !Text,
     kind :: !Text,
     version :: !(Maybe Text),
     hash :: !Text,
-    installedAt :: !Text
+    installedAt :: !Text,
+    installedFiles :: !(Maybe [Text]),
+    installedHash :: !(Maybe Text)
   }
   deriving stock (Eq, Generic, Show)
   deriving anyclass (FromJSON, ToJSON)
 
-computeKitHash :: FilePath -> [Text] -> IO Text
-computeKitHash baseDir relFiles = do
-  chunks <- mapM (readOne baseDir) (sort relFiles)
-  let digest = Hash.hash (BS.concat chunks) :: Digest SHA256
-      hex = Text.pack (show digest)
-  pure ("sha256:" <> hex)
+-- | Content hash of the listed files, which lie at @base '</>' file@
+--   below the kit checkout @root@.
+--
+--   The hashed bytes are, per file sorted by name: the file name relative
+--   to @base@, NUL, the big-endian length, the content, NUL — unchanged
+--   from earlier releases, so existing sidecars keep matching. Every file
+--   is resolved through 'safeSourcePath' first, so a symbolic link
+--   anywhere below @root@ refuses the hash instead of being read through.
+computeKitHash :: FilePath -> FilePath -> [FilePath] -> IO (Either KitError Text)
+computeKitHash root base relFiles = do
+  results <- traverse readOne relFiles
+  pure (hashEntries <$> sequence results)
   where
-    readOne :: FilePath -> Text -> IO BS.ByteString
-    readOne dir rel = do
-      safeRel <- either (ioError . userError . Text.unpack) pure (safeRelativePath rel)
-      content <- BS.readFile (dir </> safeRel)
-      let pathBytes = Text.Encoding.encodeUtf8 (Text.pack safeRel)
-          lenBytes = LBS.toStrict (runPut (putWord64be (fromIntegral (BS.length content))))
-      pure $ BS.concat [pathBytes, BS.singleton 0x00, lenBytes, content, BS.singleton 0x00]
+    readOne :: FilePath -> IO (Either KitError (FilePath, BS.ByteString))
+    readOne rel = do
+      resolved <- safeSourcePath root (base </> rel)
+      case resolved of
+        Left err -> pure (Left err)
+        Right path -> do
+          content <- try @IOException (BS.readFile path)
+          pure $ case content of
+            Left e -> Left (KitSourceUnreadable path (Text.pack (show e)))
+            Right bytes -> Right (rel, bytes)
 
+-- | The pure core: hash already-read (relative name, bytes) pairs.
+hashEntries :: [(FilePath, BS.ByteString)] -> Text
+hashEntries entries = "sha256:" <> Text.pack (show digest)
+  where
+    digest = Hash.hash (BS.concat (map chunk (sortOn fst entries))) :: Digest SHA256
+    chunk (rel, content) =
+      BS.concat
+        [ Text.Encoding.encodeUtf8 (Text.pack rel),
+          BS.singleton 0x00,
+          LBS.toStrict (runPut (putWord64be (fromIntegral (BS.length content)))),
+          content,
+          BS.singleton 0x00
+        ]
+
 sidecarPath :: AgentAssetProvider -> KitItemKind -> Text -> FilePath -> Text -> FilePath
 sidecarPath provider SkillKind itemName' targetBase sidecarName =
   targetBase
@@ -76,15 +111,11 @@
           hPutStrLn stderr $ "Warning: failed to parse sidecar " <> p <> ": " <> err
           pure Nothing
 
-writeSidecar :: AgentAssetProvider -> KitItem -> FilePath -> Text -> Text -> IO ()
-writeSidecar provider item targetBase sidecarName hashStr = do
-  meta <- newSidecarMeta item hashStr
-  let out = sidecarPath provider (kitItemKind item) (itemName item) targetBase sidecarName
-  createDirectoryIfMissing True (takeDirectory out)
-  LBS.writeFile out (encode meta)
-
-newSidecarMeta :: KitItem -> Text -> IO SidecarMeta
-newSidecarMeta item hashStr = do
+-- | Build the sidecar for one provider: the upstream content hash, the
+--   names this install writes for that provider, and the hash of the
+--   bytes it writes.
+newSidecarMeta :: KitItem -> Text -> [Text] -> Text -> IO SidecarMeta
+newSidecarMeta item hashStr writtenFiles writtenHash = do
   now <- getCurrentTime
   let stamp = Text.pack (formatTime defaultTimeLocale "%Y-%m-%dT%H:%M:%SZ" now)
   pure
@@ -93,5 +124,7 @@
         kind = itemKind item,
         version = itemVersion item,
         hash = hashStr,
-        installedAt = stamp
+        installedAt = stamp,
+        installedFiles = Just writtenFiles,
+        installedHash = Just writtenHash
       }
diff --git a/src/Baikai/Kit/Status.hs b/src/Baikai/Kit/Status.hs
--- a/src/Baikai/Kit/Status.hs
+++ b/src/Baikai/Kit/Status.hs
@@ -1,28 +1,30 @@
 module Baikai.Kit.Status
   ( KitState (..),
+    StatusReport (..),
     StatusRow (..),
+    UpstreamAvailability (..),
     classify,
     collectStatus,
     kitStatus,
     renderState,
+    renderStatusTable,
   )
 where
 
 import Baikai.AgentAssets (AgentAssetProvider, agentTargetPath, skillTargetPath)
 import Baikai.Interactive (InteractiveScope (InteractiveProjectScope))
 import Baikai.Kit.Config (KitConfig, KitScope (..), providerAgentsBase, providerLabel, sidecarFileName)
+import Baikai.Kit.Error (KitError (..))
 import Baikai.Kit.Install (loadManifestMaybe, lookupItem)
-import Baikai.Kit.Manifest (AgentEntry, KitItem (..), KitItemKind (..), agentSources, itemKind, itemVersion, kindLabel)
-import Baikai.Kit.Repo (ensureKitRepo)
+import Baikai.Kit.Manifest (KitItem, KitItemKind (..), itemKind, itemSources, itemVersion, kindLabel)
+import Baikai.Kit.Repo (RepoRefresh (..), ensureKitRepo)
 import Baikai.Kit.Sidecar (SidecarMeta, computeKitHash, readSidecar, sidecarPath)
 import Baikai.Prelude
-import Control.Exception (IOException, try)
 import Control.Monad (forM)
 import Data.List (groupBy, isPrefixOf, isSuffixOf, nub, sort, sortOn)
 import Data.Maybe (fromMaybe)
 import Data.Text qualified as Text
-import Data.Text.IO qualified as Text.IO
-import System.Directory (doesDirectoryExist, doesFileExist, listDirectory)
+import System.Directory (doesDirectoryExist, listDirectory)
 import System.FilePath (takeDirectory, (</>))
 
 data KitState
@@ -31,9 +33,29 @@
   | KitDirty
   | KitDirtyOutdated
   | KitDelisted
+  | KitUpstreamRefused
   | KitUnknown
   deriving stock (Eq, Ord, Show)
 
+-- | Whether the cached upstream could be consulted for this report.
+data UpstreamAvailability
+  = -- | The cache was refreshed and its manifest read.
+    UpstreamReady
+  | -- | The cache could not be refreshed; the rows compare against the
+    --   copy already on disk. The 'Text' is git's output.
+    UpstreamStale !Text
+  | -- | There is no usable cache: the rows say what is installed and
+    --   nothing about how it compares.
+    UpstreamUnavailable !KitError
+  deriving stock (Eq, Show)
+
+-- | What @kit status@ found, for the caller to render.
+data StatusReport = StatusReport
+  { upstream :: !UpstreamAvailability,
+    rows :: ![StatusRow]
+  }
+  deriving stock (Eq, Generic, Show)
+
 data StatusRow = StatusRow
   { name :: !Text,
     kind :: !Text,
@@ -52,6 +74,7 @@
   KitDirty -> "dirty"
   KitDirtyOutdated -> "dirty+outdated"
   KitDelisted -> "delisted"
+  KitUpstreamRefused -> "refused"
   KitUnknown -> "unknown"
 
 classify :: Maybe SidecarMeta -> Maybe KitItem -> Maybe Text -> KitState
@@ -70,22 +93,43 @@
         (False, True) -> KitDirty
         (False, False) -> KitUpToDate
 
-kitStatus :: KitConfig -> IO ()
+-- | Collect the status of everything installed. Needs no network: a kit
+--   repository that cannot be reached is reported as
+--   'UpstreamUnavailable' and the installed rows are still returned.
+kitStatus :: KitConfig -> IO StatusReport
 kitStatus config = do
-  cacheDir <- resolveCacheOrEmpty config
-  rows <- collectStatus config cacheDir [(UserScope, "user"), (ProjectScope, "project")]
-  renderStatusTable rows
+  repo <- ensureKitRepo config
+  case repo of
+    Left err -> report (UpstreamUnavailable err) ""
+    Right resolved -> do
+      let availability = case resolved ^. #refresh of
+            RepoStale err -> UpstreamStale err
+            RepoCloned -> UpstreamReady
+            RepoPulled -> UpstreamReady
+      manifest <- loadManifestMaybe (resolved ^. #dir)
+      case manifest of
+        Left err -> report (UpstreamUnavailable err) ""
+        Right Nothing -> report availability ""
+        Right (Just _) -> report availability (resolved ^. #dir)
+  where
+    report upstream cacheDir = do
+      rows <- collectStatus config cacheDir [(UserScope, "user"), (ProjectScope, "project")]
+      pure StatusReport {upstream, rows}
 
 collectStatus :: KitConfig -> FilePath -> [(KitScope, Text)] -> IO [StatusRow]
 collectStatus config cacheDir scopes = do
-  mManifest <- loadManifestMaybe cacheDir
+  -- A manifest that cannot be read is treated here as no manifest; the
+  -- report as a whole says so through 'UpstreamUnavailable'.
+  mManifest <- either (const Nothing) id <$> loadManifestMaybe cacheDir
   fmap concat . forM scopes $ \(scope, scopeText) -> do
     items <- scanInstalled config scope
     forM items $ \(provider, baseDir, itemName', scannedKind) -> do
       let mItem = lookupItem itemName' =<< mManifest
       mSidecar <- readSidecar (sidecarPath provider scannedKind itemName' baseDir (sidecarFileName config))
-      mUpstreamHash <- upstreamHash cacheDir mItem
-      let state' = classify mSidecar mItem mUpstreamHash
+      upstream <- upstreamHash cacheDir mItem
+      let state' = case upstream of
+            Left _ -> KitUpstreamRefused
+            Right mUpstreamHash -> classify mSidecar mItem mUpstreamHash
       pure
         StatusRow
           { name = itemName',
@@ -97,29 +141,25 @@
             state = state'
           }
 
-resolveCacheOrEmpty :: KitConfig -> IO FilePath
-resolveCacheOrEmpty config = do
-  result <- try @IOException (ensureKitRepo config)
-  case result of
-    Right dir -> do
-      manifestExists <- doesFileExist (dir </> "kit.json")
-      pure (if manifestExists then dir else "")
-    Left _ -> pure ""
-
-upstreamHash :: FilePath -> Maybe KitItem -> IO (Maybe Text)
-upstreamHash "" _ = pure Nothing
-upstreamHash _ Nothing = pure Nothing
-upstreamHash cacheDir (Just (KitSkillItem entry)) =
-  tryHash (cacheDir </> Text.unpack (entry ^. #path)) (entry ^. #files)
-upstreamHash cacheDir (Just (KitAgentItem entry)) =
-  tryHash (agentSourceBase cacheDir entry) (map (Text.pack . snd) (agentSources entry))
-
-tryHash :: FilePath -> [Text] -> IO (Maybe Text)
-tryHash base files = do
-  result <- try @IOException (computeKitHash base files)
-  case result of
-    Right h -> pure (Just h)
-    Left _ -> pure Nothing
+-- | The hash of an item's sources as they are in the cached checkout.
+--
+--   @Right Nothing@ means there is nothing to compare against: no cache,
+--   no manifest entry, or an upstream source that is simply gone. A
+--   'Left' means the upstream listing is one this installer refuses to
+--   read — a symbolic link, an escaping path, an unsafe manifest string —
+--   which 'collectStatus' shows as 'KitUpstreamRefused'.
+upstreamHash :: FilePath -> Maybe KitItem -> IO (Either KitError (Maybe Text))
+upstreamHash "" _ = pure (Right Nothing)
+upstreamHash _ Nothing = pure (Right Nothing)
+upstreamHash cacheDir (Just item) =
+  case itemSources item of
+    Left err -> pure (Left err)
+    Right sources -> do
+      result <- computeKitHash cacheDir (sources ^. #base) (sources ^. #files)
+      pure $ case result of
+        Left (KitSourceMissing _) -> Right Nothing
+        Left err -> Left err
+        Right h -> Right (Just h)
 
 scanInstalled :: KitConfig -> KitScope -> IO [(AgentAssetProvider, FilePath, Text, KitItemKind)]
 scanInstalled config scope = fmap concat $
@@ -148,41 +188,40 @@
       pure [(provider, Text.pack (dropAgentExtension provider f), AgentKind) | f <- files]
     else pure []
 
-renderStatusTable :: [StatusRow] -> IO ()
-renderStatusTable [] = Text.IO.putStrLn "No kit items installed."
-renderStatusTable rows = do
-  let displayRows = aggregateStatusRows rows
-      nameW = colWidth displayRows "NAME" (^. #name)
-      kindW = colWidth displayRows "TYPE" (^. #kind)
-      scopeW = colWidth displayRows "SCOPE" (^. #scope)
-      providersW = colWidth displayRows "PROVIDERS" (^. #providers)
-      instW = colWidth displayRows "INSTALLED" (renderMVer . view #installedVersion)
-      latW = colWidth displayRows "LATEST" (renderMVer . view #latestVersion)
-      hdr =
-        Text.justifyLeft (nameW + 2) ' ' "NAME"
-          <> Text.justifyLeft (kindW + 2) ' ' "TYPE"
-          <> Text.justifyLeft (scopeW + 2) ' ' "SCOPE"
-          <> Text.justifyLeft (providersW + 2) ' ' "PROVIDERS"
-          <> Text.justifyLeft (instW + 2) ' ' "INSTALLED"
-          <> Text.justifyLeft (latW + 2) ' ' "LATEST"
-          <> "STATE"
-  Text.IO.putStrLn hdr
-  mapM_ (printRow nameW kindW scopeW providersW instW latW) displayRows
+-- | The table @kit status@ prints, without a trailing newline.
+renderStatusTable :: [StatusRow] -> Text
+renderStatusTable [] = "No kit items installed."
+renderStatusTable rows = Text.intercalate "\n" (hdr : map printRow displayRows)
   where
-    colWidth displayRows colTitle f =
+    displayRows = aggregateStatusRows rows
+    nameW = colWidth "NAME" (^. #name)
+    kindW = colWidth "TYPE" (^. #kind)
+    scopeW = colWidth "SCOPE" (^. #scope)
+    providersW = colWidth "PROVIDERS" (^. #providers)
+    instW = colWidth "INSTALLED" (renderMVer . view #installedVersion)
+    latW = colWidth "LATEST" (renderMVer . view #latestVersion)
+    hdr =
+      Text.justifyLeft (nameW + 2) ' ' "NAME"
+        <> Text.justifyLeft (kindW + 2) ' ' "TYPE"
+        <> Text.justifyLeft (scopeW + 2) ' ' "SCOPE"
+        <> Text.justifyLeft (providersW + 2) ' ' "PROVIDERS"
+        <> Text.justifyLeft (instW + 2) ' ' "INSTALLED"
+        <> Text.justifyLeft (latW + 2) ' ' "LATEST"
+        <> "STATE"
+
+    colWidth colTitle f =
       maximum (Text.length colTitle : map (Text.length . f) displayRows)
 
     renderMVer = fromMaybe "-"
 
-    printRow nameW kindW scopeW providersW instW latW row =
-      Text.IO.putStrLn $
-        Text.justifyLeft (nameW + 2) ' ' (row ^. #name)
-          <> Text.justifyLeft (kindW + 2) ' ' (row ^. #kind)
-          <> Text.justifyLeft (scopeW + 2) ' ' (row ^. #scope)
-          <> Text.justifyLeft (providersW + 2) ' ' (row ^. #providers)
-          <> Text.justifyLeft (instW + 2) ' ' (renderMVer (row ^. #installedVersion))
-          <> Text.justifyLeft (latW + 2) ' ' (renderMVer (row ^. #latestVersion))
-          <> renderState (row ^. #state)
+    printRow row =
+      Text.justifyLeft (nameW + 2) ' ' (row ^. #name)
+        <> Text.justifyLeft (kindW + 2) ' ' (row ^. #kind)
+        <> Text.justifyLeft (scopeW + 2) ' ' (row ^. #scope)
+        <> Text.justifyLeft (providersW + 2) ' ' (row ^. #providers)
+        <> Text.justifyLeft (instW + 2) ' ' (renderMVer (row ^. #installedVersion))
+        <> Text.justifyLeft (latW + 2) ' ' (renderMVer (row ^. #latestVersion))
+        <> renderState (row ^. #state)
 
 aggregateStatusRows :: [StatusRow] -> [StatusRow]
 aggregateStatusRows rows =
@@ -201,12 +240,6 @@
     summarize groupRows@(firstRow : _) =
       firstRow & #providers .~ Text.intercalate "," (sort (nub (map (^. #providers) groupRows)))
     summarize [] = error "aggregateStatusRows: empty group"
-
-agentSourceBase :: FilePath -> AgentEntry -> FilePath
-agentSourceBase repoDir entry =
-  case entry ^. #files of
-    Just _ -> repoDir </> Text.unpack (entry ^. #path)
-    Nothing -> repoDir </> takeDirectory (Text.unpack (entry ^. #path))
 
 agentExtension :: AgentAssetProvider -> String
 agentExtension provider =
diff --git a/test/Main.hs b/test/Main.hs
--- a/test/Main.hs
+++ b/test/Main.hs
@@ -5,31 +5,42 @@
 import Baikai.Interactive (InteractiveProvider (InteractiveClaude, InteractiveCodex))
 import Baikai.Kit
   ( AgentEntry (..),
+    KitCommand (..),
     KitConfig (..),
+    KitError (..),
     KitItem (..),
     KitItemKind (..),
     KitManifest (..),
     KitScope (UserScope),
     KitState (..),
+    OverwritePolicy (..),
+    PlannedWrite (..),
     PullResult (..),
     RemovalOutcome (..),
     SidecarMeta (..),
     SkillEntry (..),
+    UpstreamAvailability (..),
+    WriteContent (..),
     classify,
     collectStatus,
     computeKitHash,
+    executePlanWith,
     installItem,
+    kitStatus,
+    loadManifest,
     pullKitRepo,
     readSidecar,
+    reinstallPresent,
+    renderState,
     renderUninstallReport,
+    runKit,
     safeItemName,
     safeRelativePath,
-    safeUnder,
+    safeSourcePath,
     sidecarFileName,
     sidecarPath,
     stripYamlFrontmatter,
     uninstallItem,
-    uninstallOutcomes,
     updateKit,
   )
 import Baikai.Prelude
@@ -41,11 +52,14 @@
 import Data.Text.Encoding qualified as Text.Encoding
 import System.Directory
   ( createDirectoryIfMissing,
+    createDirectoryLink,
     doesDirectoryExist,
     doesFileExist,
     doesPathExist,
     listDirectory,
     removeDirectoryRecursive,
+    removeFile,
+    renameFile,
   )
 import System.Environment (lookupEnv, setEnv, unsetEnv)
 import System.Exit (ExitCode (..))
@@ -64,10 +78,13 @@
         [ manifestTests,
           hashTests,
           pathSafetyTests,
+          symlinkSafetyTests,
           frontmatterTests,
           classifyTests,
           statusFilesystemTests,
-          installRoundTripTests
+          installRoundTripTests,
+          typedErrorTests,
+          installFidelityTests
         ]
 
 manifestTests :: TestTree
@@ -96,16 +113,16 @@
           BS.writeFile (dir </> "a.md") "alpha"
           BS.writeFile (dir </> "b.md") "beta"
           BS.writeFile (dir </> "c.md") "gamma"
-          h1 <- computeKitHash dir ["a.md", "b.md", "c.md"]
-          h2 <- computeKitHash dir ["c.md", "a.md", "b.md"]
+          h1 <- assertRight =<< computeKitHash dir "." ["a.md", "b.md", "c.md"]
+          h2 <- assertRight =<< computeKitHash dir "." ["c.md", "a.md", "b.md"]
           h1 @?= h2
           assertBool "hash should carry sha256 prefix" ("sha256:" `Text.isPrefixOf` h1),
       testCase "computeKitHash changes when file content changes" $
         withSystemTempDirectory "baikai-kit-hash-mut" $ \dir -> do
           BS.writeFile (dir </> "a.md") "alpha"
-          before <- computeKitHash dir ["a.md"]
+          before <- assertRight =<< computeKitHash dir "." ["a.md"]
           BS.writeFile (dir </> "a.md") "alpha-modified"
-          after <- computeKitHash dir ["a.md"]
+          after <- assertRight =<< computeKitHash dir "." ["a.md"]
           assertBool "hashes must differ after content change" (before /= after)
     ]
 
@@ -164,23 +181,66 @@
       testCase "safeItemName rejects multi-component and hidden names" $ do
         safeItemName "reviewer" @?= Right "reviewer"
         mapM_ (assertLeft . safeItemName) ["a/b", ".", ".hidden"],
-      testCase "safeUnder rejects an absolute right operand" $
-        assertLeft (safeUnder "/base" "/etc/passwd"),
       testCase "install refuses a manifest file path that escapes the install root" $
         withPreparedKitHome $ \home cache -> do
           BS.writeFile (cache </> "kit.json") maliciousManifestJson
-          result <- try @ExitCode (installItem testConfig "evil" UserScope)
-          result @?= Left (ExitFailure 1)
-          assertFileMissing (takeDirectory home </> "escape.txt"),
+          result <- installItem testConfig "evil" UserScope
+          assertKitError "KitUnsafePath" isUnsafePath result
+          assertFileMissing (takeDirectory home </> "escape.txt")
+          exitResult <- try @ExitCode (runKit testConfig (KitInstall "evil" UserScope))
+          exitResult @?= Left (ExitFailure 1),
       testCase "uninstall refuses a traversal name" $
         withPreparedKitHome $ \home _cache -> do
           let victim = home </> "victim"
           createDirectoryIfMissing True victim
-          result <- try @ExitCode (uninstallItem testConfig "../victim" UserScope)
-          result @?= Left (ExitFailure 1)
+          result <- uninstallItem testConfig "../victim" UserScope
+          assertKitError "KitUnsafeName" isUnsafeName result
           assertDirectoryExists victim
+          exitResult <- try @ExitCode (runKit testConfig (KitUninstall "../victim" UserScope))
+          exitResult @?= Left (ExitFailure 1)
+          assertDirectoryExists victim
     ]
 
+symlinkSafetyTests :: TestTree
+symlinkSafetyTests =
+  testGroup
+    "Symlink safety"
+    [ testCase "safeSourcePath refuses a symlinked component" $
+        withPreparedKitHome $ \home cache -> do
+          plantSymlinkedSource home cache
+          refused <- safeSourcePath cache ("skills" </> "demo" </> "sub" </> "secret.txt")
+          refused @?= Left (KitSourceSymlink (cache </> "skills" </> "demo" </> "sub"))
+          absolute <- safeSourcePath cache "/etc/passwd"
+          case absolute of
+            Left (KitUnsafePath _ _) -> pure ()
+            other -> assertFailure ("expected KitUnsafePath, got " <> show other)
+          plain <- safeSourcePath cache ("skills" </> "demo" </> "SKILL.md")
+          plain @?= Right (cache </> "skills" </> "demo" </> "SKILL.md"),
+      testCase "computeKitHash refuses a symlinked source" $
+        withPreparedKitHome $ \home cache -> do
+          plantSymlinkedSource home cache
+          hashed <- computeKitHash cache ("skills" </> "demo") ["SKILL.md", "sub" </> "secret.txt"]
+          hashed @?= Left (KitSourceSymlink (cache </> "skills" </> "demo" </> "sub")),
+      testCase "install refuses a symlinked source and writes nothing" $
+        withPreparedKitHome $ \home cache -> do
+          plantSymlinkedSource home cache
+          let claudeSkill = home </> ".config" </> "testkit" </> "agents" </> ".claude" </> "skills" </> "demo"
+          result <- installItem testConfig "demo" UserScope
+          assertKitError "KitSourceSymlink" isSourceSymlink result
+          assertFileMissing (claudeSkill </> "sub" </> "secret.txt")
+          assertFileMissing (claudeSkill </> "SKILL.md"),
+      testCase "status reports refused when upstream lists a symlinked source" $
+        withPreparedKitHome $ \home cache -> do
+          _ <- assertRight =<< installItem testConfig "demo" UserScope
+          plantSymlinkedSource home cache
+          rows <- collectStatus testConfig cache [(UserScope, "user")]
+          let demoRows = filter ((== "demo") . view #name) rows
+          assertBool "expected demo status rows" (not (null demoRows))
+          mapM_ (\row -> row ^. #state @?= KitUpstreamRefused) demoRows,
+      testCase "renderState names the refused state" $
+        renderState KitUpstreamRefused @?= "refused"
+    ]
+
 frontmatterTests :: TestTree
 frontmatterTests =
   testGroup
@@ -191,7 +251,10 @@
         stripYamlFrontmatter "---\nname: x\n---" @?= "",
       testCase "stripYamlFrontmatter leaves non-frontmatter and unterminated blocks unchanged" $ do
         stripYamlFrontmatter "Body.\n" @?= "Body.\n"
-        stripYamlFrontmatter "---\nname: x\nBody.\n" @?= "---\nname: x\nBody.\n"
+        stripYamlFrontmatter "---\nname: x\nBody.\n" @?= "---\nname: x\nBody.\n",
+      testCase "stripYamlFrontmatter normalises line endings on every branch" $ do
+        stripYamlFrontmatter "Body.\r\n" @?= "Body.\n"
+        stripYamlFrontmatter "---\r\nname: x\r\nBody.\r\n" @?= "---\nname: x\nBody.\n"
     ]
 
 statusFilesystemTests :: TestTree
@@ -209,7 +272,7 @@
             @?= codexBase </> ".codex" </> "agents" </> "reviewer.testkit-kit.json",
       testCase "delisted installed item keeps sidecar version in status" $
         withPreparedKitHome $ \_home cache -> do
-          installItem testConfig "demo" UserScope
+          _ <- assertRight =<< installItem testConfig "demo" UserScope
           BS.writeFile (cache </> "kit.json") manifestWithoutDemoJson
           rows <- collectStatus testConfig cache [(UserScope, "user")]
           let demoRows = filter ((== "demo") . view #name) rows
@@ -218,7 +281,7 @@
           mapM_ (\row -> row ^. #installedVersion @?= Just "0.1.0") demoRows,
       testCase "version and cached hash drift reports dirty+outdated" $
         withPreparedKitHome $ \_home cache -> do
-          installItem testConfig "demo" UserScope
+          _ <- assertRight =<< installItem testConfig "demo" UserScope
           BS.writeFile (cache </> "skills" </> "demo" </> "SKILL.md") "changed instructions\n"
           BS.writeFile (cache </> "kit.json") manifestWithDemoVersionJson
           rows <- collectStatus testConfig cache [(UserScope, "user")]
@@ -242,7 +305,7 @@
               codexAgent = codexBase </> ".codex" </> "agents" </> "reviewer.toml"
               claudeAgentSidecar = claudeBase </> ".claude" </> "agents" </> "reviewer.testkit-kit.json"
               codexAgentSidecar = codexBase </> ".codex" </> "agents" </> "reviewer.testkit-kit.json"
-          installItem config "demo" UserScope
+          _ <- assertRight =<< installItem config "demo" UserScope
           assertFileExists (claudeSkill </> "SKILL.md")
           assertFileExists (codexSkill </> "SKILL.md")
           assertFileExists (claudeSkill </> ".testkit-kit.json")
@@ -252,17 +315,17 @@
               (sidecar ^. #name) @?= ("demo" :: Text)
               (sidecar ^. #kind) @?= ("skill" :: Text)
             Nothing -> assertFailure "expected a skill sidecar"
-          uninstallItem config "demo" UserScope
+          _ <- assertRight =<< uninstallItem config "demo" UserScope
           assertDirectoryMissing claudeSkill
           assertDirectoryMissing codexSkill
-          installItem config "reviewer" UserScope
+          _ <- assertRight =<< installItem config "reviewer" UserScope
           assertFileExists claudeAgent
           assertFileExists codexAgent
           assertFileExists claudeAgentSidecar
           assertFileExists codexAgentSidecar
           toml <- Text.Encoding.decodeUtf8 <$> BS.readFile codexAgent
           assertBool "Codex agent TOML should contain developer instructions" ("developer_instructions" `Text.isInfixOf` toml)
-          uninstallItem config "reviewer" UserScope
+          _ <- assertRight =<< uninstallItem config "reviewer" UserScope
           assertFileMissing claudeAgent
           assertFileMissing codexAgent
           assertFileMissing claudeAgentSidecar
@@ -271,7 +334,7 @@
         withPreparedKitHome $ \home cache -> do
           let codexAgent = home </> ".codex" </> "agents" </> "reviewer.toml"
           BS.writeFile (cache </> "agents" </> "reviewer.md") "---\r\nname: reviewer\r\n---\r\nReview carefully.\r\n"
-          installItem testConfig "reviewer" UserScope
+          _ <- assertRight =<< installItem testConfig "reviewer" UserScope
           toml <- Text.Encoding.decodeUtf8 <$> BS.readFile codexAgent
           assertBool "frontmatter name should be stripped" (not ("name: reviewer" `Text.isInfixOf` toml))
           assertBool "CR characters should be stripped" (not ("\r" `Text.isInfixOf` toml)),
@@ -281,8 +344,8 @@
               claudeAgent = claudeBase </> ".claude" </> "agents" </> "reviewer.md"
               claudeAgentSidecar = claudeBase </> ".claude" </> "agents" </> "reviewer.testkit-kit.json"
           BS.writeFile (home </> ".codex") ""
-          result <- try @ExitCode (installItem testConfig "reviewer" UserScope)
-          result @?= Left (ExitFailure 1)
+          result <- installItem testConfig "reviewer" UserScope
+          assertKitError "KitWriteFailed" isWriteFailed result
           assertFileMissing claudeAgent
           assertFileMissing claudeAgentSidecar
           tmpFiles <- findFilesWithSuffix home ".baikai-kit-tmp"
@@ -296,28 +359,169 @@
           @?= "Removed stale kit metadata for 'reviewer' from user scope."
         renderUninstallReport "demo" UserScope [RemovalOutcome InteractiveClaude False False False]
           @?= "'demo' is not installed in user scope.",
-      testCase "uninstallOutcomes reports per-provider removals" $
+      testCase "uninstallItem reports per-provider removals" $
         withPreparedKitHome $ \home _cache -> do
           let codexSkill = home </> ".agents" </> "skills" </> "demo"
-          installItem testConfig "demo" UserScope
+          _ <- assertRight =<< installItem testConfig "demo" UserScope
           removeDirectoryRecursive codexSkill
-          outcomes <- uninstallOutcomes testConfig "demo" UserScope
+          outcomes <- assertRight =<< uninstallItem testConfig "demo" UserScope
           let claudeOutcome = findOutcome InteractiveClaude outcomes
               codexOutcome = findOutcome InteractiveCodex outcomes
           view #skillRemoved claudeOutcome @?= True
           view #skillRemoved codexOutcome @?= False
           view #agentRemoved codexOutcome @?= False
           view #sidecarRemoved codexOutcome @?= False,
-      testCase "pull failure is returned and update exits nonzero" $
+      testCase "pull failure is returned as a typed error" $
         withPreparedKitHome $ \_home cache -> do
           result <- pullKitRepo testConfig cache
           case result of
             PullFailed _ -> pure ()
             PullSucceeded -> assertFailure "expected fake .git cache pull to fail"
-          updateResult <- try @ExitCode (updateKit testConfig Nothing)
-          updateResult @?= Left (ExitFailure 1)
+          updateResult <- updateKit testConfig Nothing KeepLocalEdits
+          assertKitError "KitPullFailed" isPullFailed updateResult
     ]
 
+typedErrorTests :: TestTree
+typedErrorTests =
+  testGroup
+    "Typed errors"
+    [ testCase "loadManifest returns typed errors" $
+        withSystemTempDirectory "baikai-kit-manifest" $ \dir -> do
+          missing <- loadManifest dir
+          assertKitError "KitManifestMissing" isManifestMissing missing
+          BS.writeFile (dir </> "kit.json") "{"
+          invalid <- loadManifest dir
+          assertKitError "KitManifestInvalid" isManifestInvalid invalid,
+      testCase "installItem returns KitItemNotFound" $
+        withPreparedKitHome $ \_home _cache -> do
+          result <- installItem testConfig "nope" UserScope
+          assertKitError "KitItemNotFound" (== KitItemNotFound "nope") result,
+      testCase "kit status offline on a fresh HOME exits 0" $
+        withSystemTempDirectory "baikai-kit-offline" $ \tmp -> do
+          oldHome <- lookupEnv "HOME"
+          let home = tmp </> "home"
+              config = testConfig & #repoUrl .~ "file:///nonexistent-kit"
+          createDirectoryIfMissing True home
+          setEnv "HOME" home
+          flip finally (restoreHome oldHome) $ do
+            exitResult <- try @ExitCode (runKit config KitStatus)
+            exitResult @?= Right ()
+            report <- kitStatus config
+            (report ^. #rows) @?= []
+            case report ^. #upstream of
+              UpstreamUnavailable (KitCloneFailed _ _) -> pure ()
+              other -> assertFailure ("expected an unavailable upstream, got " <> show other)
+    ]
+
+installFidelityTests :: TestTree
+installFidelityTests =
+  testGroup
+    "Install fidelity"
+    [ testCase "multi-file agent installs every listed file" $
+        withPreparedKitHome $ \home cache -> do
+          plantMultiFileAgent cache
+          let claudeBase = home </> ".config" </> "testkit" </> "agents"
+              claudeAgents = claudeBase </> ".claude" </> "agents"
+              codexAgents = home </> ".codex" </> "agents"
+          _ <- assertRight =<< installItem testConfig "reviewer" UserScope
+          assertFileExists (claudeAgents </> "reviewer.md")
+          assertFileExists (claudeAgents </> "reviewer" </> "guide.md")
+          assertFileExists (codexAgents </> "reviewer.toml")
+          assertFileExists (codexAgents </> "reviewer" </> "guide.md")
+          meta <- readSidecar (claudeAgents </> "reviewer.testkit-kit.json")
+          case meta of
+            Just sidecar -> (sidecar ^. #installedFiles) @?= Just ["reviewer.md", "reviewer" <> "/" <> "guide.md"]
+            Nothing -> assertFailure "expected an agent sidecar"
+          _ <- assertRight =<< uninstallItem testConfig "reviewer" UserScope
+          assertDirectoryMissing (claudeAgents </> "reviewer")
+          assertDirectoryMissing (codexAgents </> "reviewer"),
+      testCase "phase-two failure restores the previous files" $
+        withSystemTempDirectory "baikai-kit-journal" $ \dir -> do
+          BS.writeFile (dir </> "a.txt") "old"
+          let writes =
+                [ PlannedWrite {destination = dir </> "a.txt", content = WriteBytes "new"},
+                  PlannedWrite {destination = dir </> "b.txt", content = WriteBytes "new"}
+                ]
+              failingRename temp dest
+                | "b.txt" `isSuffixOf` dest = do
+                    takeDirectory temp @?= dir
+                    assertBool "temporary should keep the tmp suffix" (".baikai-kit-tmp" `isSuffixOf` temp)
+                    assertBool "temporary name should be unique" (temp /= dest <> ".baikai-kit-tmp")
+                    ioError (userError "boom")
+                | otherwise = renameFile temp dest
+          result <- executePlanWith failingRename writes
+          case result of
+            Left (KitWriteFailed _ restored broken) -> do
+              restored @?= [dir </> "a.txt"]
+              broken @?= []
+            other -> assertFailure ("expected KitWriteFailed, got " <> show other)
+          kept <- BS.readFile (dir </> "a.txt")
+          kept @?= "old"
+          assertFileMissing (dir </> "b.txt")
+          tmpFiles <- findFilesWithSuffix dir ".baikai-kit-tmp"
+          tmpFiles @?= []
+          bakFiles <- findFilesWithSuffix dir ".baikai-kit-bak"
+          bakFiles @?= [],
+      testCase "destination directory is refused before any write" $
+        withPreparedKitHome $ \home _cache -> do
+          let claudeAgents = home </> ".config" </> "testkit" </> "agents" </> ".claude" </> "agents"
+          createDirectoryIfMissing True (claudeAgents </> "reviewer.md")
+          result <- installItem testConfig "reviewer" UserScope
+          assertKitError "KitWriteFailed" isWriteFailed result
+          assertFileMissing (home </> ".codex" </> "agents" </> "reviewer.toml"),
+      testCase "unsupported manifest version is refused" $
+        withPreparedKitHome $ \_home cache -> do
+          BS.writeFile (cache </> "kit.json") manifestWithUnsupportedVersionJson
+          loaded <- loadManifest cache
+          case loaded of
+            Left (KitManifestVersionUnsupported _ 99) -> pure ()
+            other -> assertFailure ("expected KitManifestVersionUnsupported 99, got " <> show other)
+          installed <- installItem testConfig "demo" UserScope
+          assertKitError "KitManifestVersionUnsupported" isVersionUnsupported installed,
+      testCase "a sidecar written before the installed-file fields still decodes" $
+        case Aeson.eitherDecodeStrict' legacySidecarJson :: Either String SidecarMeta of
+          Right meta -> do
+            (meta ^. #name) @?= ("demo" :: Text)
+            (meta ^. #installedFiles) @?= Nothing
+            (meta ^. #installedHash) @?= Nothing
+          Left err -> assertFailure ("expected a legacy sidecar to decode: " <> err),
+      testCase "update skips locally modified items unless forced" $
+        withPreparedKitHome $ \home cache -> do
+          let claudeSkill = home </> ".config" </> "testkit" </> "agents" </> ".claude" </> "skills" </> "demo"
+              upstream = cache </> "skills" </> "demo" </> "SKILL.md"
+          _ <- assertRight =<< installItem testConfig "demo" UserScope
+          BS.writeFile (claudeSkill </> "SKILL.md") "my edits"
+          BS.writeFile upstream "new upstream"
+          manifest <- assertRight =<< loadManifest cache
+          kept <- assertRight =<< reinstallPresent testConfig cache manifest (Just "demo") KeepLocalEdits
+          (kept ^. #skipped) @?= [("demo", UserScope)]
+          (kept ^. #updated) @?= []
+          mine <- BS.readFile (claudeSkill </> "SKILL.md")
+          mine @?= "my edits"
+          forced <- assertRight =<< reinstallPresent testConfig cache manifest (Just "demo") OverwriteLocalEdits
+          (forced ^. #updated) @?= [("demo", UserScope)]
+          (forced ^. #skipped) @?= []
+          fresh <- BS.readFile (claudeSkill </> "SKILL.md")
+          fresh @?= "new upstream"
+          -- A sidecar from before this release records no installed hash,
+          -- so the item is reinstalled without the check.
+          BS.writeFile (claudeSkill </> ".testkit-kit.json") legacySidecarJson
+          BS.writeFile (claudeSkill </> "SKILL.md") "my edits again"
+          legacy <- assertRight =<< reinstallPresent testConfig cache manifest (Just "demo") KeepLocalEdits
+          (legacy ^. #updated) @?= [("demo", UserScope)]
+          (legacy ^. #skipped) @?= [],
+      testCase "a write failure during update is returned, not thrown" $
+        withPreparedKitHome $ \home _cache -> do
+          let claudeAgents = home </> ".config" </> "testkit" </> "agents" </> ".claude" </> "agents"
+              cache = home </> ".cache" </> "testkit" </> "kit"
+          _ <- assertRight =<< installItem testConfig "reviewer" UserScope
+          removeFile (claudeAgents </> "reviewer.md")
+          createDirectoryIfMissing True (claudeAgents </> "reviewer.md")
+          manifest <- assertRight =<< loadManifest cache
+          result <- reinstallPresent testConfig cache manifest (Just "reviewer") OverwriteLocalEdits
+          assertKitError "KitWriteFailed" isWriteFailed result
+    ]
+
 decodeFixture :: FilePath -> IO KitManifest
 decodeFixture file = do
   bytes <- BS.readFile ("test/fixtures" </> file)
@@ -332,7 +536,9 @@
       kind = "skill",
       version = mVersion,
       hash = h,
-      installedAt = "2026-05-13T00:00:00Z"
+      installedAt = "2026-05-13T00:00:00Z",
+      installedFiles = Nothing,
+      installedHash = Nothing
     }
 
 mkSkillItem :: Text -> Maybe Text -> KitItem
@@ -379,10 +585,79 @@
     BS.writeFile (cache </> "kit.json") manifestJson
     setEnv "HOME" home
     action home cache `finally` restoreHome oldHome
-  where
-    restoreHome Nothing = unsetEnv "HOME"
-    restoreHome (Just value) = setEnv "HOME" value
 
+restoreHome :: Maybe String -> IO ()
+restoreHome Nothing = unsetEnv "HOME"
+restoreHome (Just value) = setEnv "HOME" value
+
+-- | Plant a committed-symlink kit: a directory link out of the checkout
+--   and a manifest that lists a file below it.
+plantSymlinkedSource :: FilePath -> FilePath -> IO ()
+plantSymlinkedSource home cache = do
+  let outsideDir = takeDirectory home </> "outside"
+  createDirectoryIfMissing True outsideDir
+  BS.writeFile (outsideDir </> "secret.txt") "top secret\n"
+  createDirectoryLink outsideDir (cache </> "skills" </> "demo" </> "sub")
+  BS.writeFile (cache </> "kit.json") manifestWithSymlinkedFileJson
+
+manifestWithSymlinkedFileJson :: BS.ByteString
+manifestWithSymlinkedFileJson =
+  Text.Encoding.encodeUtf8 $
+    Text.concat
+      [ "{\"version\":2,",
+        "\"skills\":[{",
+        "\"name\":\"demo\",",
+        "\"description\":\"Demo skill\",",
+        "\"version\":\"0.1.0\",",
+        "\"path\":\"skills/demo\",",
+        "\"files\":[\"SKILL.md\",\"sub/secret.txt\"]",
+        "}],",
+        "\"agents\":[]} "
+      ]
+
+-- | Rewrite the fixture kit so its agent lists two files below a
+--   directory of its own.
+plantMultiFileAgent :: FilePath -> IO ()
+plantMultiFileAgent cache = do
+  createDirectoryIfMissing True (cache </> "agents" </> "reviewer")
+  BS.writeFile (cache </> "agents" </> "reviewer" </> "reviewer.md") "---\nname: reviewer\n---\nReview carefully.\n"
+  BS.writeFile (cache </> "agents" </> "reviewer" </> "guide.md") "How to review.\n"
+  BS.writeFile (cache </> "kit.json") manifestWithMultiFileAgentJson
+
+manifestWithMultiFileAgentJson :: BS.ByteString
+manifestWithMultiFileAgentJson =
+  Text.Encoding.encodeUtf8 $
+    Text.concat
+      [ "{\"version\":2,",
+        "\"skills\":[],",
+        "\"agents\":[{",
+        "\"name\":\"reviewer\",",
+        "\"description\":\"Review agent\",",
+        "\"version\":\"0.1.0\",",
+        "\"path\":\"agents/reviewer\",",
+        "\"files\":[\"reviewer.md\",\"guide.md\"]",
+        "}]} "
+      ]
+
+manifestWithUnsupportedVersionJson :: BS.ByteString
+manifestWithUnsupportedVersionJson =
+  Text.Encoding.encodeUtf8 $
+    Text.concat
+      [ "{\"version\":99,",
+        "\"skills\":[{",
+        "\"name\":\"demo\",",
+        "\"description\":\"Demo skill\",",
+        "\"version\":\"0.1.0\",",
+        "\"path\":\"skills/demo\",",
+        "\"files\":[\"SKILL.md\"]",
+        "}],",
+        "\"agents\":[]} "
+      ]
+
+legacySidecarJson :: BS.ByteString
+legacySidecarJson =
+  "{\"name\":\"demo\",\"kind\":\"skill\",\"version\":\"0.1.0\",\"hash\":\"sha256:x\",\"installedAt\":\"t\"}"
+
 manifestJson :: BS.ByteString
 manifestJson =
   Text.Encoding.encodeUtf8 $
@@ -451,6 +726,41 @@
         "}],",
         "\"agents\":[]} "
       ]
+
+isUnsafePath :: KitError -> Bool
+isUnsafePath = \case KitUnsafePath _ _ -> True; _ -> False
+
+isUnsafeName :: KitError -> Bool
+isUnsafeName = \case KitUnsafeName _ _ -> True; _ -> False
+
+isSourceSymlink :: KitError -> Bool
+isSourceSymlink = \case KitSourceSymlink _ -> True; _ -> False
+
+isWriteFailed :: KitError -> Bool
+isWriteFailed = \case KitWriteFailed {} -> True; _ -> False
+
+isPullFailed :: KitError -> Bool
+isPullFailed = \case KitPullFailed _ -> True; _ -> False
+
+isManifestMissing :: KitError -> Bool
+isManifestMissing = \case KitManifestMissing _ -> True; _ -> False
+
+isVersionUnsupported :: KitError -> Bool
+isVersionUnsupported = \case KitManifestVersionUnsupported _ _ -> True; _ -> False
+
+isManifestInvalid :: KitError -> Bool
+isManifestInvalid = \case KitManifestInvalid _ _ -> True; _ -> False
+
+assertKitError :: (Show a) => String -> (KitError -> Bool) -> Either KitError a -> IO ()
+assertKitError label matches result =
+  case result of
+    Left err | matches err -> pure ()
+    other -> assertFailure ("expected " <> label <> ", got " <> show other)
+
+assertRight :: (Show e) => Either e a -> IO a
+assertRight = \case
+  Right value -> pure value
+  Left err -> assertFailure ("expected Right, got Left " <> show err)
 
 assertLeft :: (Show b) => Either a b -> IO ()
 assertLeft result =
