refactor(agent): publish agent/inbox/claimed from Inbox.claim

Move the claimed-message notification loop out of the loop's pre-step
into Inbox.claim(target, turn), so the step-boundary operation publishes
its own claimed notifications like insertions and discards do.

packages/tasks/tasks-local/tests/tasks.spec.ts

@@ -23,7 +23,7 @@ function stubAgent(ctx: Context, rawId: string): Agent {
     id,
     options: {},
     session,
-    inbox: new Inbox(session, { inserted: () => {}, discarded: () => {} }),
+    inbox: new Inbox(session, { inserted: () => {}, discarded: () => {}, claimed: () => {} }),
     status: 'idle' as const,
     ctx: scopeFiber.ctx,
     send: () => {},