first pass of merging in warp (doesn't build)

app/src/local_control/handlers.rs

@@ -0,0 +1,19 @@
+//! App-side action handlers invoked by the local-control bridge.
+use ::local_control::{ActionKind, InstanceId};
+use serde_json::json;
+
+pub(super) mod app_state;
+pub(super) mod close;
+pub(super) mod layout;
+pub(super) mod metadata;
+pub(super) mod metadata_config;
+pub(super) mod settings_surfaces;
+
+/// Standard acknowledgement payload shared by mutation handlers.
+pub(crate) fn ack(instance_id: &Option<InstanceId>, action: ActionKind) -> serde_json::Value {
+    json!({
+        "action": action.as_str(),
+        "ok": true,
+        "instance_id": instance_id.as_ref().map(|id| id.0.as_str()),
+    })
+}