fix(extension): preserve existing tab scope semantics

apps/extension/src/session-manager/__tests__/manager.test.ts

@@ -175,6 +175,15 @@ describe("SessionManager", () => {
       reservation.commit({ tabId: 42, originalWindowId: 7, originalIndex: 3 });
       expect(isAgentControlledTab(ctx, 42)).toBe(true);
     });
+
+    it("forgets an agent-created tab after Chrome removes it", async () => {
+      const sm = new SessionManager({ agentWindow: fakeAgentWindow() });
+      const ctx = await sm.start("aa11");
+      ctx.agentCreatedTabs.add(42);
+      sm.forgetAgentCreatedTab(42);
+      expect(ctx.agentCreatedTabs.has(42)).toBe(false);
+      expect(isAgentControlledTab(ctx, 0)).toBe(true);
+    });
   });
 
   describe("findBorrowingSession", () => {

apps/extension/src/session-manager/manager.ts

@@ -117,6 +117,13 @@ export class SessionManager {
     return Array.from(this.sessions.values());
   }
 
+  /** Remove a closed tab from agent-created ownership tracking. */
+  forgetAgentCreatedTab(tabId: number): void {
+    for (const ctx of this.sessions.values()) {
+      ctx.agentCreatedTabs.delete(tabId);
+    }
+  }
+
   /**
    * Look up whether `tabId` is currently borrowed by some *other*
    * session than the one calling. Used by M8 `tab_borrow` to refuse