diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,14 @@
 # Revision history for kiroku-metrics
 
+## 0.3.0.1 — 2026-10-20
+
+### Bug Fixes
+
+- Keep sanitized 503 responses for typed `ConnectionLost`,
+  `PoolAcquisitionTimeout` and `TransientTransactionFailure` store failures.
+  Permanent server errors use the sanitized 500 response. Existing envelope
+  fields, messages and route-specific unavailable codes are preserved.
+
 ## 0.3.0.0 — 2026-10-11
 
 ### Breaking Changes
diff --git a/kiroku-metrics.cabal b/kiroku-metrics.cabal
--- a/kiroku-metrics.cabal
+++ b/kiroku-metrics.cabal
@@ -1,6 +1,6 @@
 cabal-version:   3.0
 name:            kiroku-metrics
-version:         0.3.0.0
+version:         0.3.0.1
 synopsis:
   Metrics, health, and event-streaming HTTP endpoints for Kiroku
 
diff --git a/src/Kiroku/Metrics/JSON.hs b/src/Kiroku/Metrics/JSON.hs
--- a/src/Kiroku/Metrics/JSON.hs
+++ b/src/Kiroku/Metrics/JSON.hs
@@ -62,5 +62,8 @@
 storeErrorResponse :: Text -> StoreError -> Response
 storeErrorResponse unavailableCode = \case
     ConnectionError _ -> errorResponse status503 unavailableCode "The event store is unavailable." Nothing
+    ConnectionLost _ -> errorResponse status503 unavailableCode "The event store is unavailable." Nothing
+    PoolAcquisitionTimeout -> errorResponse status503 unavailableCode "The event store is unavailable." Nothing
+    TransientTransactionFailure _ _ -> errorResponse status503 unavailableCode "The event store is unavailable." Nothing
     EventDecodeFailed _ -> errorResponse status500 "event_decode_failed" "An event could not be decoded." Nothing
     _ -> errorResponse status500 "store_error" "The event store operation failed." Nothing
diff --git a/test/Test/BrowseSpec.hs b/test/Test/BrowseSpec.hs
--- a/test/Test/BrowseSpec.hs
+++ b/test/Test/BrowseSpec.hs
@@ -8,6 +8,7 @@
 import Data.Aeson (Value (..), object, (.=))
 import Data.Aeson qualified as Aeson
 import Data.Aeson.KeyMap qualified as KM
+import Data.ByteString qualified as BS
 import Data.ByteString.Builder (toLazyByteString)
 import Data.ByteString.Lazy qualified as LBS
 import Data.Generics.Labels ()
@@ -59,6 +60,14 @@
         (disabled, _, disabledBody) <- capture browseNotConfiguredApp "GET" ["streams"]
         disabled `shouldBe` status404
         code disabledBody `shouldBe` Just "store_browsing_not_configured"
+    it "sanitizes typed transient and permanent failures on browse routes" $ do
+        forM_ [(Store.ConnectionLost "secret", status503, "store_unavailable"), (Store.PoolAcquisitionTimeout, status503, "store_unavailable"), (Store.TransientTransactionFailure "40001" "secret", status503, "store_unavailable"), (Store.TransientTransactionFailure "40P01" "secret", status503, "store_unavailable"), (Store.UnexpectedServerError "42P01" "secret SQL", status500, "store_error")] $ \(err, expected, expectedCode) -> do
+            let app = browseApp (StoreBrowser (\_ -> pure (Left err)) defaultBrowseLimits)
+            (status, headers, responseBody) <- capture app "GET" ["events"]
+            status `shouldBe` expected
+            code responseBody `shouldBe` Just expectedCode
+            responseBody `shouldSatisfy` (not . BS.isInfixOf "secret" . LBS.toStrict)
+            capture app "HEAD" ["events"] `shouldReturn` (status, headers, "")
     it "serves all browse routes, names and exclusive pages through the shared server" $ withTestStore $ \store -> do
         append store "orders-1" 3
         append store "orders-2" 1
diff --git a/test/Test/CheckpointsSpec.hs b/test/Test/CheckpointsSpec.hs
--- a/test/Test/CheckpointsSpec.hs
+++ b/test/Test/CheckpointsSpec.hs
@@ -88,7 +88,7 @@
         readIORef calls `shouldReturn` 2
 
     it "sanitizes typed failures and preserves HEAD error status and headers" $ do
-        let failures = [(Store.ConnectionError "postgres://secret", status503, "checkpoint_inventory_unavailable"), (Store.StreamNotFound (Store.StreamName "secret"), status500, "store_error"), (Store.EventDecodeFailed (DecodeFailure (Store.EventId UUID.nil) "secret"), status500, "event_decode_failed")]
+        let failures = [(Store.ConnectionError "postgres://secret", status503, "checkpoint_inventory_unavailable"), (Store.ConnectionLost "secret", status503, "checkpoint_inventory_unavailable"), (Store.PoolAcquisitionTimeout, status503, "checkpoint_inventory_unavailable"), (Store.TransientTransactionFailure "40001" "secret", status503, "checkpoint_inventory_unavailable"), (Store.TransientTransactionFailure "40P01" "secret", status503, "checkpoint_inventory_unavailable"), (Store.UnexpectedServerError "42P01" "secret SQL", status500, "store_error"), (Store.StreamNotFound (Store.StreamName "secret"), status500, "store_error"), (Store.EventDecodeFailed (DecodeFailure (Store.EventId UUID.nil) "secret"), status500, "event_decode_failed")]
         forM_ failures $ \(err, expected, expectedCode) -> do
             let app = checkpointsApp (pure (Left err))
             (status, headers, body) <- capture app "GET"
diff --git a/test/Test/CorsSpec.hs b/test/Test/CorsSpec.hs
--- a/test/Test/CorsSpec.hs
+++ b/test/Test/CorsSpec.hs
@@ -173,7 +173,7 @@
             errorEnvelope "origin_not_allowed" "Denied." Nothing `shouldBe` object ["error" .= object ["code" .= ("origin_not_allowed" :: Text), "message" .= ("Denied." :: Text)]]
             errorEnvelope "invalid_query_parameter" "Invalid." (Just (object ["parameter" .= ("limit" :: Text)])) `shouldBe` object ["error" .= object ["code" .= ("invalid_query_parameter" :: Text), "message" .= ("Invalid." :: Text), "details" .= object ["parameter" .= ("limit" :: Text)]]]
         it "sanitizes unavailable and other store errors" $ do
-            forM_ [(ConnectionError "postgres://secret", status503, "store_unavailable"), (StreamNotFound (StreamName "private"), status500, "store_error"), (EventDecodeFailed (DecodeFailure (EventId UUID.nil) "secret payload"), status500, "event_decode_failed")] $ \(err, expected, code) -> do
+            forM_ [(ConnectionError "postgres://secret", status503, "store_unavailable"), (ConnectionLost "secret", status503, "store_unavailable"), (PoolAcquisitionTimeout, status503, "store_unavailable"), (TransientTransactionFailure "40001" "secret", status503, "store_unavailable"), (TransientTransactionFailure "40P01" "secret", status503, "store_unavailable"), (UnexpectedServerError "42P01" "secret SQL", status500, "store_error"), (StreamNotFound (StreamName "private"), status500, "store_error"), (EventDecodeFailed (DecodeFailure (EventId UUID.nil) "secret payload"), status500, "event_decode_failed")] $ \(err, expected, code) -> do
                 (status, _, body) <- capture (\_ respond -> respond (storeErrorResponse "store_unavailable" err)) "GET" []
                 status `shouldBe` expected
                 errorCode body `shouldBe` Just (String code)
diff --git a/test/Test/DeadLettersSpec.hs b/test/Test/DeadLettersSpec.hs
--- a/test/Test/DeadLettersSpec.hs
+++ b/test/Test/DeadLettersSpec.hs
@@ -81,7 +81,7 @@
         missing `shouldBe` status404
         code body `shouldBe` Just "dead_letters_not_configured"
     it "sanitizes typed store failures and preserves HEAD error headers" $ do
-        forM_ [(Store.ConnectionError "postgres://secret", status503, "dead_letters_unavailable"), (Store.StreamNotFound (Store.StreamName "secret"), status500, "store_error"), (Store.EventDecodeFailed (Store.DecodeFailure (Store.EventId UUID.nil) "secret"), status500, "event_decode_failed")] $ \(err, expected, expectedCode) -> do
+        forM_ [(Store.ConnectionError "postgres://secret", status503, "dead_letters_unavailable"), (Store.ConnectionLost "secret", status503, "dead_letters_unavailable"), (Store.PoolAcquisitionTimeout, status503, "dead_letters_unavailable"), (Store.TransientTransactionFailure "40001" "secret", status503, "dead_letters_unavailable"), (Store.TransientTransactionFailure "40P01" "secret", status503, "dead_letters_unavailable"), (Store.UnexpectedServerError "42P01" "secret SQL", status500, "store_error"), (Store.StreamNotFound (Store.StreamName "secret"), status500, "store_error"), (Store.EventDecodeFailed (Store.DecodeFailure (Store.EventId UUID.nil) "secret"), status500, "event_decode_failed")] $ \(err, expected, expectedCode) -> do
             let app = deadLettersApp (\_ -> pure (Left err))
             (status, headers, body) <- capture app "GET" route []
             status `shouldBe` expected