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/web.rs

@@ -128,6 +128,9 @@ pub async fn serve(addr: &str, state: AppState) -> anyhow::Result<()> {
         // Protocol 14 (§20.8): open one Dangerous Treasures event. The plugin remembers the key;
         // DT picks the spot and despawns its own chest, so nothing here is kept either.
         .route("/dt/start", post(dt_start))
+        // Protocol 14 (§20.9): place one guarded crate. The plugin remembers the key; the crate is
+        // kept when the run ends (Guarded Crate cannot end one alone), so nothing is kept here.
+        .route("/gc/place", post(gc_place))
         // Protocol 10 (§29): who took part, what they may redeem, and a line in chat. The tally
         // is counted and held by the plugin, the kit catalogue is Kits' own, and whether a chat
         // line was already said is the plugin's memory. These move lines, like everything above.
@@ -573,6 +576,13 @@ async fn dt_start(State(st): State<AppState>, Json(body): Json<Value>) -> Respon
     forward_object(&st, body, "dt.start", "a Dangerous Treasures start").await
 }
 
+/// Place one guarded crate for a run's step (protocol 14). `gc.placed` (where it landed, and
+/// `repeat` for a key already seen) or `gc.error` with a reason, `npcspawn-missing` among them.
+/// Guarded Crate ends its own event, so nothing is remembered here.
+async fn gc_place(State(st): State<AppState>, Json(body): Json<Value>) -> Response {
+    forward_object(&st, body, "gc.place", "a guarded crate placement").await
+}
+
 /// Start counting who takes part in a run. `tally.ok` or `tally.error` with a reason.
 async fn tally_open(State(st): State<AppState>, Json(body): Json<Value>) -> Response {
     forward_object(&st, body, "tally.open", "a tally").await
@@ -1319,6 +1329,23 @@ mod tests {
         assert!(stamp(json!(2), "dt.start", "r-61").is_none());
     }
 
+    /// Protocol 14, Guarded Crate: a placement is stamped `gc.place` whatever its body names, so
+    /// the route can place a guarded crate and nothing else, and its key, event and location pass
+    /// through.
+    #[test]
+    fn protocol_14_gc_place_is_stamped() {
+        let body = json!({ "cmd": "dt.start", "reqId": "theirs", "key": "12:4", "event": "Elite", "monument": "powerplant_1", "offsetX": 10.0 });
+        let stamped = stamp(body, "gc.place", "r-62").expect("an object is stamped");
+
+        assert_eq!(stamped["cmd"], "gc.place");
+        assert_eq!(stamped["reqId"], "r-62");
+        assert_eq!(stamped["key"], "12:4");
+        assert_eq!(stamped["event"], "Elite");
+        assert_eq!(stamped["monument"], "powerplant_1");
+        assert_eq!(stamped["offsetX"], 10.0);
+        assert!(stamp(json!("Elite"), "gc.place", "r-63").is_none());
+    }
+
     /// Protocol 12: a title set is forwarded whole. The markup inside each `text` is the module's
     /// and the plugin's business, so it must arrive byte for byte as the website composed it.
     #[test]