fix(ui): hidden retained chat panes silently clear unread for sessions you are not viewing (#123247)

Since retained panes (#121625) every pane — hidden or presented — keeps
its sessions subscription alive, and applySessionsState marked the
pane's selected session read unconditionally. New activity in a
recently-viewed session was cleared by its hidden pane instantly: the
sidebar unread dot never stuck, agentStatus attention was wiped by the
read patch, and "Mark as unread" self-reverted. Gate the read-marking
on this.presented, matching applyActiveSessionBindings.

ui/src/pages/chat/chat-pane-context.ts

@@ -105,7 +105,11 @@ export abstract class ChatPaneContext extends ChatPaneLifecycle {
     this.refreshSwarmRoster();
     const selectedSession = selectedChatSessionRow(state);
     if (applySelectedSessionProjection(state, selectedSession)) {
-      this.markSessionRead(selectedSession);
+      // Hidden retained panes keep this subscription alive; only the pane the
+      // user is actually looking at may clear unread/attention state.
+      if (this.presented) {
+        this.markSessionRead(selectedSession);
+      }
     }
     this.syncSessionSuggestionTarget(
       stateValue.agentId ?? resolveChatAgentId(state) ?? "main",

ui/src/pages/chat/chat-pane.read-marker.test.ts

@@ -89,4 +89,44 @@ describe("chat pane read markers", () => {
     expect(state.chatError).toBeNull();
     expect(state.lastError).toBeNull();
   });
+
+  it("does not clear unread from a hidden retained pane", () => {
+    const patch = vi.fn().mockResolvedValue(null);
+    const { pane } = createTestChatPane({
+      client: {} as GatewayBrowserClient,
+      sessions: { patch } as unknown as SessionCapability,
+    });
+    const sessionsState = (presented: boolean) => {
+      pane.presented = presented;
+      pane.applySessionsState({
+        result: {
+          sessions: [
+            {
+              key: "agent:main:current",
+              kind: "direct",
+              label: "Background activity",
+              updatedAt: 20,
+              unread: true,
+            },
+          ],
+        },
+        agentId: "main",
+        loading: false,
+        error: null,
+        deletedSessions: [],
+      } as unknown as Parameters<typeof pane.applySessionsState>[0]);
+    };
+
+    // Hidden retained panes keep the subscription alive but must not mark
+    // the session read — the user is not looking at it.
+    sessionsState(false);
+    expect(patch).not.toHaveBeenCalled();
+
+    sessionsState(true);
+    expect(patch).toHaveBeenCalledWith(
+      "agent:main:current",
+      { unread: false },
+      { agentId: "main" },
+    );
+  });
 });

ui/src/pages/chat/chat-pane.test-support.ts

@@ -134,6 +134,7 @@ export type TestChatPane = HTMLElement & {
   headerPlacementReclaimingKey: string | null;
   reclaimHeaderPlacement: (row: GatewaySessionRow) => Promise<void>;
   markSessionRead: (row: GatewaySessionRow | undefined) => void;
+  applySessionsState: (stateValue: ApplicationContext["sessions"]["state"]) => void;
   renderPaneHeader: (
     workspace: ReturnType<typeof createSessionWorkspaceProps>,
     tasks: ReturnType<typeof createBackgroundTasksProps>,