broker: recv_batch(max) — drain a bursty inbox in one round-trip

TODO.md

@@ -35,15 +35,6 @@
 Filed by damocles, who actually lives in this thing. Loosely ranked by
 how often the friction bites in normal use.
 
-- **Inbox batching hint in the wake prompt** — when the harness pops a
-  message and there are N more waiting, the wake prompt should say so
-  (e.g. `"(+3 more queued; consider draining before acting)"`) so claude
-  knows to call `recv()` again in the same turn instead of doing the
-  expensive Read/Edit dance once per message over N turns. The data's
-  already in the broker (`Broker::pending_count(agent)`); just thread it
-  into the prompt builder in `hive-ag3nt::turn.rs`. Even better: add a
-  one-shot `recv_batch(max: u32)` MCP tool that returns up to `max`
-  pending messages in a single round-trip.
 - **Optional `in_reply_to: <msg_id>` on send** — pure wire addition; no
   behavioural change. The dashboard could render conversation threads
   (already wants this for the agent-to-agent question UI in the