fix(server-runtime): preserve explicit empty route destinations (#1324)

---------

Co-authored-by: Neko <neko@ayaka.moe>
Co-authored-by-agent: Sisyphus <clio-agent@sisyphuslabs.ai>
Co-authored-by-agent: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

packages/server-runtime/src/middlewares/route.test.ts

@@ -93,6 +93,22 @@ describe('route middleware', () => {
     expect(collectDestinations(event)).toEqual(['label:env=prod'])
   })
 
+  it('treats an explicit empty route destination list as the override', () => {
+    const event = createSparkNotifyEvent({
+      data: {
+        id: 'evt-override',
+        eventId: 'spark-override',
+        kind: 'ping',
+        urgency: 'soon',
+        headline: 'hello',
+        destinations: ['module:character'],
+      },
+      route: { destinations: [] },
+    })
+
+    expect(collectDestinations(event)).toEqual([])
+  })
+
   it('matches destinations by label selector', () => {
     const peer = createPeer({
       id: 'peer-2',

packages/server-runtime/src/middlewares/route.ts

@@ -79,7 +79,7 @@ export function createPolicyMiddleware(policy: RoutingPolicy): RouteMiddleware {
 }
 
 export function collectDestinations(event: WebSocketEvent | (Omit<WebSocketEvent, 'metadata'> & Partial<Pick<WebSocketEvent, 'metadata'>>)) {
-  if (event.route?.destinations?.length) {
+  if (event.route?.destinations !== undefined) {
     return event.route.destinations
   }