fix(acp): report end_turn for non-client turn aborts

TurnEndReasonMap aborted endings no longer map to 'cancelled': the ACP
spec reserves StopReason::Cancelled for the client's own session/cancel
notification (plus disposal, both settled out of band). A turn aborted by
a hook or another agent owner is ordinary quiescence and now settles as
end_turn, matching the README/note contract. interrupted keeps
'cancelled' as the crash-orphan marker.

packages/acp/acp/src/codec.ts

@@ -17,7 +17,11 @@ export function turnEndToStopReason(reason: TurnEndReason): StopReason {
       return 'end_turn'
     case 'max-tokens':
       return 'max_tokens'
+    // `cancelled` is reserved for explicit client cancellation (`session/cancel`)
+    // and disposal, both settled out of band; a turn aborted by a hook or
+    // another owner is ordinary quiescence and reports `end_turn`.
     case 'aborted':
+      return 'end_turn'
     case 'interrupted':
       return 'cancelled'
     case 'blocked':

packages/acp/acp/tests/codec.spec.ts

@@ -6,7 +6,7 @@ describe('ACP codec', () => {
   it.each([
     [{ kind: 'completed' }, 'end_turn'],
     [{ kind: 'max-tokens' }, 'max_tokens'],
-    [{ kind: 'aborted', reason: { kind: 'user' } }, 'cancelled'],
+    [{ kind: 'aborted', reason: { kind: 'user' } }, 'end_turn'],
     [{ kind: 'interrupted' }, 'cancelled'],
     [{ kind: 'blocked' }, 'end_turn'],
     [{ kind: 'error', error: { message: 'failed', code: 'UNKNOWN' } }, 'end_turn'],

packages/acp/acp/tests/turns.spec.ts

@@ -166,6 +166,18 @@ describe('ACP prompt lifecycle', () => {
       .toEqual({ kind: 'aborted', reason: { kind: 'user' } })
   })
 
+  it('settles a hook-cancelled turn as end_turn, not cancelled', async () => {
+    harness = await makeBridgeHarness({ script: ['hang'] })
+    const sessionId = await newSession(harness)
+    const prompt = harness.client.prompt({ sessionId, prompt: [{ type: 'text', text: 'go' }] })
+    const agent = harness.ctx.agents.get(SessionId(sessionId))!
+    await vi.waitFor(() => { expect(agent.status).toBe('running') })
+    // A hook or another owner cancels the agent: the ACP client never called
+    // session/cancel, so this is ordinary quiescence and reports end_turn.
+    agent.cancel({ kind: 'hook', reason: 'owner intervention' })
+    await expect(prompt).resolves.toEqual({ stopReason: 'end_turn' })
+  })
+
   it('cancels autonomous running work without an in-flight prompt', async () => {
     harness = await makeBridgeHarness({ script: ['hang'] })
     const sessionId = await newSession(harness)