diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,17 @@
+# 0.9.1.0
+
+* Add `yieldToPureList`
+
+# 0.9.0.0
+
+* Add quantified constraint `forall e es. (e <: es) => OneWayCoercible
+  (h e) (h es)` as a superclass of `Handle h`
+
+* Improve performance of `mapHandle` by using `unsafeOneWayCoerce`.
+  This can violate type safety if a `OneWayCoercibleInstance` is
+  invalid, so do not define or use invalid `OneWayCoercible`
+  instances!
+
 # 0.8.2.0
 
 * Improve performance of `Reader` and `DslBuilderEff`
diff --git a/bluefin-internal.cabal b/bluefin-internal.cabal
--- a/bluefin-internal.cabal
+++ b/bluefin-internal.cabal
@@ -1,6 +1,6 @@
 cabal-version:      3.0
 name:               bluefin-internal
-version:            0.9.0.0
+version:            0.9.1.0
 license:            MIT
 license-file:       LICENSE
 author:             Tom Ellis
diff --git a/src/Bluefin/Internal.hs b/src/Bluefin/Internal.hs
--- a/src/Bluefin/Internal.hs
+++ b/src/Bluefin/Internal.hs
@@ -1334,6 +1334,12 @@
   (as, r) <- yieldToReverseList f
   pure (reverse as, r)
 
+-- | Gather all yielded elements into a list, purely.  Can be used
+-- when only when there are no other capabilities in scope, besides
+-- the 'Yield'.
+yieldToPureList :: (forall e. Yield a e -> Eff e r) -> ([a], r)
+yieldToPureList f = runPureEff $ yieldToList $ \y -> useImpl (f y)
+
 -- |
 -- @
 -- >>> runPureEff $ withYieldToList $ \\y -> do
@@ -2051,6 +2057,8 @@
   Eff es r
 runAskCapability = runHandleReader
 
+-- | Do not use @askCapability@.  It is unsafe and will be removed in
+-- a future version.  Use 'asksCapability' instead.
 askCapability ::
   (e <: es, Handle h) =>
   HandleReader h e ->
diff --git a/test/Main.hs b/test/Main.hs
--- a/test/Main.hs
+++ b/test/Main.hs
@@ -34,12 +34,21 @@
       "List"
       (runPureEff (yieldToList (listEff ([20, 30, 40], "Hello"))))
       ([20, 30, 40], "Hello")
+    assertEqual'
+      "Pure list"
+      ( yieldToPureList $ \y -> do
+          yield y 20
+          yield y 30
+          pure "Hello"
+      )
+      ([20, 30], "Hello")
 
     test_localInHandler y
     test_generalBracket io y
     test_streamConsumeReader y
     test_streamConsumeHandleReader y
     test_unliftIOReader io y
+    test_askCapabilityEscape y
 
 (!?) :: [a] -> Int -> Maybe a
 xs !? i = runPureEff $
@@ -175,3 +184,15 @@
             assertEqual spech "myLocal" i i'
         )
         (\x -> effToIO . local r (const x) . effIO io)
+
+test_askCapabilityEscape :: (e <: es) => SpecH e -> Eff es ()
+test_askCapabilityEscape y = runConstEffect False $ \cFalse ->
+  runAskCapability cFalse $ \(ac :: HandleReader (ConstEffect Bool) e) -> do
+    -- We should not be allowed to escape `escaped` like this.  A
+    -- future version of Bluefin should fix this by removing
+    -- `askCapability`.
+    escaped <- runConstEffect True $ \cTrue -> do
+      localCapability ac (const (mapHandle cTrue)) $ do
+        useImpl (askCapability @_ @e ac)
+    let MkConstEffect escapedValue = escaped
+    assertEqual y "askCapability escape" True escapedValue