add agent-facing compact tool gated on context usage

docs/turn-loop/mcp.md

@@ -110,6 +110,19 @@ at_unix_timestamp?)`, `request_next_turn()`.
   `homeserver`); omitted for agents with no matrix provisioning. Omit
   `name` to query self.
 
+**Always-on, no tool group** (like `set_status`): `compact()`.
+
+- `compact` — agent self-service equivalent of the operator dashboard's
+  `/compact` button. No args. Gated server-side on the last completed
+  turn's context usage: refused (with an explanation, no side effect)
+  unless usage is above 66% of the effective context window. On a
+  pass, queues the same deferred `compact_pending` flag the dashboard
+  button sets — consumed at the end of the current turn, so it never
+  races a live claude process, and the usual pre-compaction
+  notes-checkpoint turn still fires first. Dispatched through the
+  in-agent socket (`hive-agent-sock::Request::Compact`), not the
+  broker — see `hive-agent/src/todo_server.rs`.
+
 ## Privileged tools (by tool group)
 
 - **Bash execution** (`execution`) — background shell tasks. See