refactor: add authoritative revalidation on app resume and reconnect

packages/server/src/shared/messages.stream-parsing.test.ts

@@ -15,6 +15,7 @@ describe('shared messages stream parsing', () => {
       payload: {
         requestId: 'req-1',
         agentId: 'agent_live',
+        agent: null,
         direction: 'tail',
         projection: 'projected',
         epoch: 'epoch-1',

packages/server/src/shared/messages.ts

@@ -1594,6 +1594,7 @@ export const FetchAgentTimelineResponseMessageSchema = z.object({
   payload: z.object({
     requestId: z.string(),
     agentId: z.string(),
+    agent: AgentSnapshotPayloadSchema.nullable(),
     direction: z.enum(['tail', 'before', 'after']),
     projection: z.enum(['projected', 'canonical']),
     epoch: z.string(),