test(native-chat): make composition frames carry isComposing, not just inputType

This suite's comment claimed "Gating onChange on `isComposing` breaks here."
It did not. composeFrame() fired `input` with `inputType` but never set
`isComposing`, so a gate on `isComposing` passed all four tests untouched —
the suite asserted a discriminator it did not exercise.

Composition frames now carry both, so neither gate is exempt. Verified by
pointing the mutant at it: with an `isComposing` gate on the composer's
onChange, this suite now fails 3 of 4 (it passed 4 of 4 before), and the
ordinary-English arm correctly survives, since a composition gate should not
touch it. Production code is unchanged and stays gate-free; the mutation was
applied, measured, and reverted.

Found while excluding NativeChatView's question-card remount as the owner of
#12118 / STA-3219: the remount is real, but the preedit survives it precisely
because this write path has no composition gate.

src/renderer/src/components/native-chat/native-chat-question-card-composition-survival.test.tsx

@@ -190,7 +190,14 @@ function setInteractivePrompt(prompt: string | null, rendered: ReturnType<typeof
  *  `value` without this is what made the loss look real. */
 function composeFrame(el: HTMLTextAreaElement, value: string, data: string): void {
   fireEvent.compositionUpdate(el, { data })
-  fireEvent.input(el, { target: { value }, inputType: 'insertCompositionText', data })
+  // `isComposing` is set as well as `inputType`: a gate on either one is a plausible
+  // regression, and omitting it silently exempted the `isComposing` variant.
+  fireEvent.input(el, {
+    target: { value },
+    inputType: 'insertCompositionText',
+    data,
+    isComposing: true
+  })
 }
 
 describe('native chat question card vs an in-flight composition', () => {
@@ -257,7 +264,10 @@ describe('native chat question card vs an in-flight composition', () => {
 
     // The mechanism, pinned directly: onChange fires on composition `input`
     // frames, so the draft cache — not the unmounted DOM node — is what carries
-    // the preedit across the swap. Gating onChange on `isComposing` breaks here.
+    // the preedit across the swap. Gating onChange on either `isComposing` or
+    // `inputType` breaks here — the frames now carry both, so neither gate is
+    // exempt. Previously only `inputType` was set, so an `isComposing` gate
+    // passed this suite untouched despite the claim.
     setInteractivePrompt(ASK_USER_QUESTION, rendered)
     expect(readNativeChatDraftCache(PANE_KEY)).toBe('가')
   })