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/pty/pty-local/tests/local.spec.ts

@@ -35,8 +35,9 @@ function stubAgent(ctx: Context, rawId: string): Agent {
   const scope = ctx.plugin(() => {})
   const session = Session.create(id)
   return {
-    id, options: {}, session, inbox: new Inbox(session, { inserted: () => {}, discarded: () => {} }),
-    status: 'idle', ctx: scope.ctx,
+    id, options: {}, session, inbox: new Inbox(session, { inserted: () => {}, discarded: () => {}, claimed: () => {} }),
+    status: 'idle',
+    ctx: scope.ctx,
     send: () => {},
     followup: () => {}, steer: () => {}, inject: () => {}, cancel() {},
     runMaintenance: task => task(new AbortController().signal),