diff --git a/src/vs/sessions/services/sessions/browser/sessionsService.ts b/src/vs/sessions/services/sessions/browser/sessionsService.ts
index d28754f327637..f8167bafac8e9 100644
--- a/src/vs/sessions/services/sessions/browser/sessionsService.ts
+++ b/src/vs/sessions/services/sessions/browser/sessionsService.ts
@@ -472,6 +472,9 @@ export class SessionsService extends Disposable implements ISessionsService {
 		// no slot remains); drive the open flow below so the fallback is fully
 		// opened.
 		if (e.removed.length) {
+			for (const session of e.removed) {
+				this._sessionStates.delete(session.resource);
+			}
 			this._visibility.removeMany(e.removed.map(r => r.sessionId));
 		}
 
@@ -886,6 +889,26 @@ export class SessionsService extends Disposable implements ISessionsService {
 
 	private _saveSessionStates(): void {
 		const entries = this._snapshotVisibleSessionStates();
+
+		// Also persist the per-session state (closed chats, last active chat) of
+		// sessions that are not currently visible, so a session switched out of
+		// the grid keeps its closed-chat set across a reload. Grid-placement
+		// fields are stripped so they are not restored into the grid.
+		const visible = new ResourceMap<true>();
+		for (const entry of entries) {
+			visible.set(URI.parse(entry.sessionResource), true);
+		}
+		for (const [resource, state] of this._sessionStates) {
+			if (visible.has(resource)) {
+				continue;
+			}
+			entries.push({
+				sessionResource: state.sessionResource,
+				activeChatResource: state.activeChatResource,
+				closedChatResources: state.closedChatResources,
+			});
+		}
+
 		this.storageService.store(ACTIVE_SESSION_STATES_KEY, JSON.stringify(entries), StorageScope.WORKSPACE, StorageTarget.MACHINE);
 	}
 
diff --git a/src/vs/sessions/services/sessions/test/browser/sessionsManagementService.test.ts b/src/vs/sessions/services/sessions/test/browser/sessionsManagementService.test.ts
index 4dd446a0af1bd..af94e90a61efc 100644
--- a/src/vs/sessions/services/sessions/test/browser/sessionsManagementService.test.ts
+++ b/src/vs/sessions/services/sessions/test/browser/sessionsManagementService.test.ts
@@ -1404,6 +1404,62 @@ suite('SessionsManagementService', () => {
 			await second.restoreVisibleSessions();
 			assert.deepStrictEqual((second.activeSession.get()?.closedChats.get() ?? []).map(c => c.title.get()), ['b']);
 		});
+
+		test('a chat closed in a non-active session stays closed across a restart', async () => {
+			const mainA = chat('mainA');
+			const chatA2 = chat('a2');
+			const sessionA = stubSession({
+				sessionId: 'A', providerId: 'test',
+				status: constObservable(SessionStatus.Completed),
+				chats: constObservable([mainA, chatA2]),
+				mainChat: constObservable(mainA),
+				capabilities: constObservable({ supportsMultipleChats: true }),
+			});
+			const mainB = chat('mainB');
+			const chatB2 = chat('b2');
+			const sessionB = stubSession({
+				sessionId: 'B', providerId: 'test',
+				status: constObservable(SessionStatus.Completed),
+				chats: constObservable([mainB, chatB2]),
+				mainChat: constObservable(mainB),
+				capabilities: constObservable({ supportsMultipleChats: true }),
+			});
+			const storage = disposables.add(new InMemoryStorageService());
+			const provider = new class extends TestSessionsProvider {
+				constructor() { super(sessionA); }
+				override getSessions(): ISession[] { return [sessionA, sessionB]; }
+			};
+			const makeView = () => {
+				const instantiationService = disposables.add(new TestInstantiationService());
+				instantiationService.stub(IStorageService, storage);
+				instantiationService.stub(ILogService, new NullLogService());
+				instantiationService.stub(IContextKeyService, disposables.add(new MockContextKeyService()));
+				instantiationService.stub(ISessionsProvidersService, new TestSessionsProvidersService([provider]));
+				instantiationService.stub(IUriIdentityService, { extUri: extUriBiasedIgnorePathCase });
+				instantiationService.stub(IChatWidgetService, new TestChatWidgetService());
+				instantiationService.stub(IProgressService, new TestProgressService());
+				instantiationService.stub(IChatService, new class extends mock<IChatService>() {
+					override readonly onDidSubmitRequest = Event.None;
+				});
+				const service = disposables.add(instantiationService.createInstance(SessionsManagementService));
+				return createView(instantiationService, service, disposables);
+			};
+
+			// First window: close a chat in each session, end on session A so B is
+			// no longer visible, then simulate shutdown (flush storage).
+			const first = makeView();
+			await first.openSession(sessionB.resource);
+			await first.closeChat(first.activeSession.get()!, chatB2);
+			await first.openSession(sessionA.resource);
+			await first.closeChat(first.activeSession.get()!, chatA2);
+			await storage.flush();
+
+			// Second window: restore, then switch to B and confirm its chat is still closed.
+			const second = makeView();
+			await second.restoreVisibleSessions();
+			await second.openSession(sessionB.resource);
+			assert.deepStrictEqual((second.activeSession.get()?.closedChats.get() ?? []).map(c => c.title.get()), ['b2']);
+		});
 	});
 
 	suite('createQuickChat', () => {