docs: drop history/rationale framing from recv docs, state current behavior only

docs/turn-loop/mcp.md

@@ -36,10 +36,8 @@ ttl_seconds?, to?)`, `answer(id, answer)`, `ack_until(up_to)`.
   `[ "operator" ]` to restrict a sub-agent to operator messages only
   (the topology parent is always reachable regardless of this list —
   that carve-out is structural, keyed on parent relationship, not name).
-- `recv` — drain inbox. Always an immediate peek, never blocks (#2814
-  — dropped the `wait_seconds` long-poll param entirely; nobody had a
-  use case for it that wasn't already better served by ending the
-  turn). `max` (default 1, cap 5) drains up to N rows. Each returned row is prefixed with
+- `recv` — drain inbox. Always an immediate peek, never blocks. `max`
+  (default 1, cap 5) drains up to N rows. Each returned row is prefixed with
   `[msg #<id>]` (broker row id; note the highest id seen, then pass
   it to `ack_until` to bulk-triage the batch). **Graceful shutdown**: when the harness
   receives a stop signal, the inbox becomes fenced and `recv` returns an