parallelize graceful agent drains, serialize container stops on fast lane; unify shutdown+checkpoint+compact prompt

docs/turn-loop.md

@@ -517,6 +517,12 @@ ttl_seconds?, to?)`, `answer(id, answer)`.
   explicit `from: "graceful-stop"` message instead of an empty inbox.
   This unmissably directs the agent to flush durable state (`/state`
   files) and end the turn — the container exits when the turn completes.
+  This is a **single** wake: the graceful-stop turn *is* the checkpoint
+  (its prompt carries the full notes/CLAUDE.md/TODO.md flush guidance),
+  so the harness compacts directly afterwards if the context crossed the
+  watermark (`CompactionMode::CompactOnly`) rather than waking a second
+  dedicated checkpoint turn. Compacting before shutdown keeps a later
+  cold start cheap instead of re-uploading a huge transcript.
 - `ask` — surface a structured question to the operator (default) or
   a peer agent (`to: "<agent>"`). Non-blocking — returns a question
   id; the answer arrives as a `question_answered` system event in the