dashboard: POST /api/rebuild-queue/{id}/cancel for queued entries (closes #447)

hive-c0re/src/dashboard.rs

@@ -77,6 +77,7 @@ pub async fn serve(port: u16, coord: Arc<Coordinator>) -> Result<()> {
         .route("/api/schedules", get(api_schedules).post(post_schedule_new))
         .route("/api/schedules/{id}/cancel", post(post_schedule_cancel))
         .route("/api/schedules/{id}/fire-now", post(post_schedule_fire_now))
+        .route("/api/rebuild-queue/{id}/cancel", post(post_rebuild_queue_cancel))
         .route("/dashboard/stream", get(dashboard_stream))
         .route("/dashboard/history", get(dashboard_history))
         // Anything not matched by the dynamic routes above falls
@@ -1459,6 +1460,28 @@ async fn post_schedule_fire_now(
     }
 }
 
+/// `POST /api/rebuild-queue/{id}/cancel` — drop a `Queued` entry
+/// from the rebuild queue (#447). Refuses `Running` / terminal
+/// entries: an in-flight rebuild owns the agent's nix store +
+/// nixos-container update lock and can't be safely interrupted
+/// from the queue side. Always returns 200; the body is
+/// `{"cancelled": true}` on a successful flip from Queued →
+/// Cancelled, `{"cancelled": false}` when the row was Running /
+/// terminal / gone. On success a fresh `RebuildQueueChanged`
+/// snapshot fires so the row's state flip surfaces live.
+async fn post_rebuild_queue_cancel(
+    State(state): State<AppState>,
+    AxumPath(id): AxumPath<u64>,
+) -> Response {
+    let cancelled = state.coord.rebuild_queue.cancel(id);
+    if cancelled {
+        state.coord.emit_rebuild_queue_snapshot();
+        axum::Json(serde_json::json!({"cancelled": true})).into_response()
+    } else {
+        axum::Json(serde_json::json!({"cancelled": false})).into_response()
+    }
+}
+
 #[derive(serde::Deserialize, Default)]
 struct CancelScheduleForm {
     /// `None` / absent / empty array → cancel whole schedule.