fix(tasks): bind cleanup and notices to exact owners

Task records previously retained only ownerSession. If an old agent scope unwound after another agent reused the same agent and session ids, cleanup selected both records and could cancel replacement work. The completion surface also re-resolved the session at settlement, which could inject an old task notice into the replacement agent.

Retain the exact Agent instance for lifecycle work, select owner cleanup by object identity, and pass that exact owner to completion listeners. Keep read, list, kill, and wait authorization session-based as the runtime RFC intends. Add regressions for cleanup and notice routing under id reuse, then update the public docs and generated API catalogs.

packages/tasks/tool-tasks/src/index.ts

@@ -93,19 +93,15 @@ export function apply(ctx: Context, config: Config): void {
     text: 'Track every background task id you start. You are notified in-session when a task finishes — do not busy-poll or sleep on one; keep working on independent steps and do not duplicate a running task\'s work. Before giving a final answer, collect every still-relevant task with task_output (set wait: true only when you are genuinely blocked on it), and task_kill tasks that stopped mattering.',
   })
 
-  // Background completion → inject a notice into the owning agent's session.
-  // `ctx.get('agents')` (not static inject): this listener runs from a
-  // detached settlement continuation on the tasks fiber — a foreign fiber —
-  // where the `ctx.agents` property proxy would throw; `ctx.get` is the
-  // topology-independent lookup. No registry mounted → drop the notice.
-  ctx.tasks.onTaskDone((snapshot) => {
+  // Background completion → inject a notice through the exact lifecycle owner.
+  // Re-resolving by a reusable agent/session id could target a replacement
+  // while the old owner's scope is still unwinding.
+  ctx.tasks.onTaskDone((snapshot, owner) => {
     // A reported terminal state was already surfaced by an explicit
     // read/wait/kill response — a notice would be a redundant "finished".
-    if (snapshot.reported || snapshot.ownerSession === undefined) return
-    const agent = ctx.get('agents')?.list().find(a => a.session.header.id === snapshot.ownerSession)
-    if (!agent) return
+    if (snapshot.reported || owner === undefined) return
     try {
-      agent.inject(
+      owner.inject(
         [{ type: 'text', text: `background task ${snapshot.id} (${snapshot.kind}: ${snapshot.label}) finished ${statusLine(snapshot)}. Read its output with task_output.` }],
         { source: { kind: 'plugin', plugin: 'tool-tasks' } },
       )