fix(sync): preserve mixed-client delivery guarantees

packages/app/src/panels/agent-panel.tsx

@@ -907,7 +907,7 @@ function ChatAgentContent({
     if (!agentId) {
       return;
     }
-    if (agentState.id) {
+    if (agentState.id && hasAppliedAuthoritativeHistory) {
       if (missingAgentState.kind === "resolving" || missingAgentState.kind === "not_found") {
         setMissingAgentState(reconcileMissingAgentStateWithPresentAgent);
       }
@@ -964,6 +964,7 @@ function ChatAgentContent({
       });
   }, [
     agentState.id,
+    hasAppliedAuthoritativeHistory,
     agentId,
     client,
     ensureAgentIsInitialized,

packages/server/src/server/session.test.ts

@@ -4592,6 +4592,8 @@ test("unions viewed timelines across socket sources and removes detached sources
   session.updateClientCapabilities({ selective_agent_timeline: true });
   const firstSocket = {};
   const secondSocket = {};
+  session.updateClientCapabilities({ selective_agent_timeline: true }, firstSocket);
+  session.updateClientCapabilities({ selective_agent_timeline: true }, secondSocket);
 
   await session.handleMessage(
     {
@@ -4635,6 +4637,22 @@ test("unions viewed timelines across socket sources and removes detached sources
   });
   expect(messages.filter((message) => message.type === "agent_stream")).toHaveLength(2);
 
+  const legacySocket = {};
+  session.updateClientCapabilities(null, legacySocket);
+  messages.length = 0;
+  forward({
+    type: "agent_stream",
+    agentId: "agent-not-viewed",
+    event: {
+      type: "timeline",
+      provider: "mock",
+      item: { type: "assistant_message", messageId: "message-legacy", text: "legacy" },
+    },
+  });
+  expect(messages.some((message) => message.type === "agent_stream")).toBe(true);
+
+  session.clearAgentTimelineSubscription(legacySocket);
+
   session.clearAgentTimelineSubscription(firstSocket);
   messages.length = 0;
   forward({

packages/server/src/server/session.ts

@@ -585,6 +585,7 @@ export class Session {
   private unsubscribeAgentEvents: (() => void) | null = null;
   private viewedTimelineAgentIds = new Set<string>();
   private readonly viewedTimelineAgentIdsBySource = new Map<object, Set<string>>();
+  private readonly selectiveTimelineCapabilityBySource = new Map<object, boolean>();
   private readonly defaultTimelineSubscriptionSource = {};
   private unsubscribeTerminalWorkspaceContributionEvents: (() => void) | null = null;
   private readonly agentUpdates: AgentUpdatesService;
@@ -966,17 +967,25 @@ export class Session {
     }
   }
 
-  updateClientCapabilities(capabilities: Record<string, unknown> | null): void {
+  updateClientCapabilities(capabilities: Record<string, unknown> | null, source?: object): void {
     this.clientCapabilities = parseClientCapabilities(capabilities);
-    if (!this.supports(CLIENT_CAPS.selectiveAgentTimeline)) {
+    if (source) {
+      this.selectiveTimelineCapabilityBySource.set(
+        source,
+        this.supports(CLIENT_CAPS.selectiveAgentTimeline),
+      );
+    }
+    if (!source && !this.supports(CLIENT_CAPS.selectiveAgentTimeline)) {
       this.viewedTimelineAgentIdsBySource.clear();
       this.viewedTimelineAgentIds.clear();
     }
   }
 
   clearAgentTimelineSubscription(source: object): void {
-    if (!this.viewedTimelineAgentIdsBySource.delete(source)) return;
-    this.rebuildViewedTimelineAgentIds();
+    this.selectiveTimelineCapabilityBySource.delete(source);
+    if (this.viewedTimelineAgentIdsBySource.delete(source)) {
+      this.rebuildViewedTimelineAgentIds();
+    }
   }
 
   private replaceAgentTimelineSubscription(source: object | undefined, agentIds: string[]): void {
@@ -994,6 +1003,16 @@ export class Session {
     this.viewedTimelineAgentIds = viewedAgentIds;
   }
 
+  private usesSelectiveTimelineDelivery(): boolean {
+    if (this.selectiveTimelineCapabilityBySource.size === 0) {
+      return this.supports(CLIENT_CAPS.selectiveAgentTimeline);
+    }
+    for (const capable of this.selectiveTimelineCapabilityBySource.values()) {
+      if (!capable) return false;
+    }
+    return true;
+  }
+
   supports(capability: ClientCapability): boolean {
     return this.clientCapabilities.has(capability);
   }
@@ -1308,10 +1327,7 @@ export class Session {
           "agent.session.forward_stream",
         );
 
-        if (
-          this.supports(CLIENT_CAPS.selectiveAgentTimeline) &&
-          serializedEvent.type === "attention_required"
-        ) {
+        if (this.usesSelectiveTimelineDelivery() && serializedEvent.type === "attention_required") {
           this.emit({
             type: "agent_attention_required",
             payload: {
@@ -1325,7 +1341,7 @@ export class Session {
             },
           });
         } else if (
-          !this.supports(CLIENT_CAPS.selectiveAgentTimeline) ||
+          !this.usesSelectiveTimelineDelivery() ||
           this.viewedTimelineAgentIds.has(event.agentId)
         ) {
           this.emit({
@@ -1587,7 +1603,12 @@ export class Session {
         return this.handleProviderSubagentTimelineRequest(msg);
       case "agent.timeline.set_subscription.request": {
         const agentIds = [...new Set(msg.agentIds)].sort();
-        if (this.supports(CLIENT_CAPS.selectiveAgentTimeline)) {
+        if (
+          source
+            ? (this.selectiveTimelineCapabilityBySource.get(source) ??
+              this.supports(CLIENT_CAPS.selectiveAgentTimeline))
+            : this.supports(CLIENT_CAPS.selectiveAgentTimeline)
+        ) {
           this.replaceAgentTimelineSubscription(source, agentIds);
         }
         this.emit({
@@ -4590,6 +4611,7 @@ export class Session {
         "fetch_workspaces_response_ready",
       );
       const snapshot = this.buildBootstrapSnapshot(payload.entries);
+      this.seedWorkspaceSubscriptionSnapshot(subscriptionId, payload.entries);
 
       this.emit({
         type: "fetch_workspaces_response",
@@ -4650,6 +4672,20 @@ export class Session {
     return { snapshotByWorkspaceId };
   }
 
+  private seedWorkspaceSubscriptionSnapshot(
+    subscriptionId: string | null,
+    entries: FetchWorkspacesResponseEntry[],
+  ): void {
+    const subscription = this.workspaceUpdatesSubscription;
+    if (!subscriptionId || subscription?.subscriptionId !== subscriptionId) return;
+    for (const entry of entries) {
+      subscription.lastEmittedByWorkspaceId.set(entry.id, {
+        kind: "upsert",
+        workspace: entry,
+      });
+    }
+  }
+
   private async registerWorkspaceForImportedAgent(
     workspace: PersistedWorkspaceRecord,
   ): Promise<void> {

packages/server/src/server/websocket-server.ts

@@ -1093,6 +1093,7 @@ export class VoiceAssistantWebSocketServer {
       sockets: new Set([ws]),
       externalDisconnectCleanupTimeout: null,
     };
+    session.updateClientCapabilities(clientCapabilities, ws);
     return connection;
   }
 
@@ -1166,7 +1167,7 @@ export class VoiceAssistantWebSocketServer {
       // COMPAT(selectiveAgentTimeline): added in v0.1.106. Every capable resumed
       // hello resets membership before server_info so stale retained-session
       // state cannot leak. Remove after 2027-01-12.
-      existing.session.updateClientCapabilities(newClientCapabilities);
+      existing.session.updateClientCapabilities(newClientCapabilities, ws);
       if (
         JSON.stringify(existing.clientCapabilities ?? null) !==
         JSON.stringify(newClientCapabilities ?? null)