fix(scope): harden final ownership boundaries

packages/ui/acp/src/index.ts

@@ -1010,7 +1010,7 @@ export function apply(ctx: Context, config: AcpConfig): void {
    * quiescence"): for each session settle any pending prompt `cancelled`, then
    * run that session's {@link AgentHandle} `dispose()` — which stops the loop
    * (sets `disposed`, aborts the in-flight step), AWAITS the loop's exit (the
-   * final `turn/end` + `session/flush` are captured while `onAppend` is still
+   * final `turn/end` + `session/flush` are captured while the store-owned append observer is still
    * attached), unregisters the agent, and removes its session from the store.
    * The per-session disposes run in parallel. Idempotent — clears the `sessions`
    * map first and memoizes, so a second call (close racing dispose) is a no-op.

packages/ui/acp/tests/dispose.spec.ts

@@ -159,8 +159,8 @@ describe('acp bridge — disposal & HMR safety', () => {
   it('the final turn closing events are persisted across an AgentHandle dispose (durability)', async () => {
     // The teardown-ORDER guarantee: a per-agent dispose must stop the loop,
     // AWAIT its exit (so the loop's final `turn/end` + `session/flush` fire
-    // through the still-attached `session.onAppend` → `session/event`), and only
-    // THEN detach onAppend + remove the session. If the order were inverted
+    // through the still-attached store observer → `session/event`), and only
+    // THEN detach that observer + remove the session. If the order were inverted
     // (detach first), the closing events would never reach persistence. Drive a
     // CLEAN turn to completion, dispose JUST the bridge, then re-load the
     // persisted log from disk and assert the closing turn/end is on disk — the
@@ -190,7 +190,7 @@ describe('acp bridge — disposal & HMR safety', () => {
     // produced BY the dispose itself. Here the model stream HANGS, so the turn is
     // still open when teardown runs: the composite agent effect stops the loop,
     // the loop unwinds and appends `turn/end {disposed}` + runs its final
-    // `session/flush` — all while `onAppend` is still attached (the session
+    // `session/flush` — all while the store-owned append observer is still attached (the session
     // detach is the LAST disposer in the same effect's LIFO chain) — and only
     // THEN is the session detached. If the order were inverted (or the session
     // were a racing SIBLING effect), the abort-produced `turn/end` would never
@@ -255,7 +255,7 @@ describe('acp bridge — disposal & HMR safety', () => {
     // into ONE composite effect whose disposers run as a `.then()` chain. The
     // register disposer emits `agent/disposed`; if a listener throws and the
     // emit is UNCONTAINED, the rejected chain skips the LATER session-detach
-    // disposer — stranding the session in the store with `onAppend` attached (a
+    // disposer — stranding the session in the store with its append observer attached (a
     // leak AND a durability hole, since the new design relies on detach
     // running). The emit must be contained. Register a throwing listener, drive
     // a clean turn, dispose, and assert the session was STILL removed.