feat(director): add authored camera directions and anchors

src/ui/navigationController.js

@@ -1,3 +1,4 @@
+import { createStateChannel } from '../app/stateChannel.js';
 import * as Cesium from 'cesium';
 import {
   beginDeferredNavigation,
@@ -34,6 +35,9 @@ export class NavigationController {
       cancelOrientation,
     });
     this._navigationGeneration = 0;
+    this._cameraHandoffs = createStateChannel(() => ({
+      generation: this._navigationGeneration,
+    }));
     this._activeLocationSearchGeneration = null;
     this._disposed = false;
   }
@@ -45,6 +49,7 @@ export class NavigationController {
     const { flightsLayer, militaryFlightsLayer, satellitesLayer } =
       this.tracking;
     this._navigationGeneration += 1;
+    this._cameraHandoffs?.publish();
     // A newer destination owns the camera, so the last free-text search is no
     // longer where we are. DEFERRED navigation opts out here and clears at the
     // reassert seam instead: a geocode that never resolves moves no camera, and
@@ -247,8 +252,14 @@ export class NavigationController {
       },
     });
   }
+  /** Subscribe to ownership changes without claiming the camera or exposing mutable state. */
+  subscribeCameraHandoff(listener) {
+    return this._cameraHandoffs.subscribe(listener, { emitCurrent: false });
+  }
   stop() {
     this._disposed = true;
+    this._cameraHandoffs?.publish();
+    this._cameraHandoffs?.destroy();
   }
   destroy() {
     this.stop();