feat(sidecar): protocol 14 — the guarded crate placement forward (PLAN_REDESIGNS §14.3.5)

POST /gc/place stamps the body gc.place and forwards it; the plugin keeps the
key and the crate is kept when the run ends, so nothing is kept here. Spec:
docs rust-link/PROTOCOL.md §20.9.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01E14m6SuuY6i1vASFeGDBeY

sidecar/src/main.rs

@@ -203,6 +203,11 @@ use tracing_subscriber::EnvFilter;
 /// retry never opens a second; DT despawns its own chest. `dt.started`, `dt.won` and `dt.ended`
 /// ride the feed like any other event.
 ///
+/// Guarded Crate (§20.9, the module's PLAN_REDESIGNS.md §14.3.5) adds one forward,
+/// `POST /gc/place`: place one guarded crate for a run's step. The plugin remembers the key so a
+/// retry never places a second; the crate is kept when the run ends (D373). `gc.started`,
+/// `gc.ended` and `gc.failed` ride the feed like any other event.
+///
 /// `docs/rust-link/PROTOCOL.md` is the specification — §8 the read path, §9 identity, §10 the
 /// mirror, §11 configuration, §12 clans, §13 the raid frame, §14 the leases, §15 the world verbs,
 /// §16 the rewards, §17 the map, §18 the optional mods, §19 the walk's fixes, §20 the step editor;