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/goal/command-goal/tests/command-goal.spec.ts

@@ -20,7 +20,7 @@ interface Harness {
 function stubAgent(ctx: Context, id: string): { agent: Agent; session: Session } {
   // Store-created: the command executor durably logs lifecycle events on it.
   const session = ctx.sessions.create(SessionId(id))
-  const inbox = new Inbox(session, { inserted: () => {}, discarded: () => {} })
+  const inbox = new Inbox(session, { inserted: () => {}, discarded: () => {}, claimed: () => {} })
   let status: AgentStatus = 'idle'
   const agent: Agent = {
     id: session.id,