sessions: persist main chat rename across restore for agent host (#323785)

* sessions: persist main chat rename across restore for agent host

For agent host multichat sessions, renaming the default/main chat sets an
independent title persisted on the host as customChatTitle:<defaultChatUri>.
However restoreSession always re-seeded the default chat with an empty title
(inherit the session title), so after a process restart or idle eviction the
main chat tab reverted to the session title. Peer chats were already restored
via _restorePeerChats.

Read the persisted default-chat title on restore and seed it back through
restoreSession/_ensureDefaultChat, mirroring the peer-chat restore path.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* sessions: clarify _readPersistedChatTitle doc comment

Addresses CCR feedback: the helper now reads the default chat's title too,
not only peer chats.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

---------

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

.github/skills/sessions/SKILL.md

@@ -61,6 +61,8 @@ Then read the relevant spec for the area you are changing (see table below). If
 
 Whenever the user flags a wrong pattern, rejects an approach, or gives design/rules feedback, **automatically add it** as a concise pitfall/learning to this `Common Pitfalls` section (or the most relevant spec doc) in the same change — without being asked again. Keep each entry 1–3 sentences: the anti-pattern, why it is wrong, and the preferred pattern.
 
+- **Default/main chat title persistence differs per provider — don't unify them**: For the **agent host**, the default (main) chat title is independent of the session title (`AgentHostSessionAdapter._defaultChatTitleOverride`, persisted on the host as `customChatTitle:<defaultChatUri>`); it must be seeded back on restore via `restoreSession`/`_ensureDefaultChat` (mirroring `_restorePeerChats`), or it reverts to the session title after a process restart / idle eviction. For the **local chat sessions provider** (`localChatSessionsProvider`), the primary chat and the session intentionally **share one `_title` observable**, so renaming the first/main chat updates the session title live — this is by design; do not "fix" it to be independent. Only additional (non-primary) local chats have their own title.
+
 ## Validating Changes
 
 You **must** run these checks before declaring work complete:

src/vs/platform/agentHost/node/agentHostStateManager.ts

@@ -598,7 +598,7 @@ export class AgentHostStateManager extends Disposable {
 	 * notification because the session is already known to clients via
 	 * `listSessions`.
 	 */
-	restoreSession(summary: SessionSummary, turns: Turn[], options?: { readonly draft?: Message }): SessionState {
+	restoreSession(summary: SessionSummary, turns: Turn[], options?: { readonly draft?: Message; readonly defaultChatTitle?: string }): SessionState {
 		const key = summary.resource;
 		const existing = this._sessionStates.get(key);
 		if (existing) {
@@ -611,7 +611,7 @@ export class AgentHostStateManager extends Disposable {
 			lifecycle: SessionLifecycle.Ready,
 		};
 		this._sessionStates.set(key, this._newEntry(state, summary));
-		this._ensureDefaultChat(key, summary, turns, options?.draft);
+		this._ensureDefaultChat(key, summary, turns, options?.draft, options?.defaultChatTitle);
 		this._summaryNotifier.announce(key, summary);
 
 		this._logService.trace(`[AgentHostStateManager] Restored session: ${key} (${turns.length} turns)`);
@@ -631,13 +631,11 @@ export class AgentHostStateManager extends Disposable {
 	 * at creation/restore time, so the snapshot a client later receives on
 	 * subscribe already reflects the default chat.
 	 */
-	private _ensureDefaultChat(sessionKey: string, summary: SessionSummary, turns?: Turn[], draft?: Message): void {
+	private _ensureDefaultChat(sessionKey: string, summary: SessionSummary, turns?: Turn[], draft?: Message, defaultChatTitle?: string): void {
 		const chatUri = buildDefaultChatUri(sessionKey);
-		// The default chat starts with an empty title so it inherits the session
-		// title for display. It only gets its own title when renamed independently
-		// (via a per-chat `SessionChatUpdated`). This keeps the session title and
-		// the default chat tab title independent.
-		const chatSummary: ChatSummary = { ...createDefaultChatSummary(summary, chatUri), title: '' };
+		// Empty title means "inherit the session title"; a persisted independent
+		// rename (`defaultChatTitle`) is seeded back here so it survives restore.
+		const chatSummary: ChatSummary = { ...createDefaultChatSummary(summary, chatUri), title: defaultChatTitle ?? '' };
 		this._chatStates.set(chatUri, { ...createChatState(chatSummary), turns: turns ?? [], draft });
 		const entry = this._sessionStates.get(sessionKey);
 		if (entry) {

src/vs/platform/agentHost/node/agentService.ts

@@ -1673,8 +1673,12 @@ export class AgentService extends Disposable implements IAgentService {
 			_meta: sessionMetadata
 		};
 
-		const defaultDraft = await this._getChatDraft(session, URI.parse(buildDefaultChatUri(sessionStr)));
-		this._stateManager.restoreSession(summary, [...turns], { draft: defaultDraft });
+		const defaultChatUri = URI.parse(buildDefaultChatUri(sessionStr));
+		const [defaultDraft, defaultChatTitle] = await Promise.all([
+			this._getChatDraft(session, defaultChatUri),
+			this._readPersistedChatTitle(session, defaultChatUri),
+		]);
+		this._stateManager.restoreSession(summary, [...turns], { draft: defaultDraft, defaultChatTitle });
 
 		const promises: Promise<unknown>[] = [];
 		// Eagerly register subagent child sessions discovered in the event log
@@ -1798,7 +1802,7 @@ export class AgentService extends Disposable implements IAgentService {
 		}
 	}
 
-	/** Reads a peer chat's persisted custom title, if any. */
+	/** Reads a chat's persisted custom title (default or peer chat), if any. */
 	private async _readPersistedChatTitle(session: URI, chatUri: URI): Promise<string | undefined> {
 		const ref = await this._sessionDataService.tryOpenDatabase?.(session);
 		if (!ref) {

src/vs/platform/agentHost/test/node/agentService.test.ts

@@ -2501,6 +2501,25 @@ suite('AgentService (node dispatcher)', () => {
 			});
 		});
 
+		test('restoreSession restores the default chat\'s independently-renamed title', async () => {
+			const db = new TestSessionDatabase();
+			const localService = disposables.add(new AgentService(new NullLogService(), fileService, createSessionDataService(db), { _serviceBrand: undefined } as IProductService, createNoopGitService()));
+			localService.registerProvider(copilotAgent);
+			await copilotAgent.createSession();
+			const sessionResource = (await copilotAgent.listSessions())[0].session;
+			copilotAgent.sessionMessages = [];
+
+			// The host persists an independent default-chat rename under this key;
+			// restore must seed it back or the main chat tab reverts to the session title.
+			const defaultChatUri = buildDefaultChatUri(sessionResource.toString());
+			await db.setMetadata(`customChatTitle:${defaultChatUri}`, 'Renamed Default Chat');
+
+			await localService.restoreSession(sessionResource);
+
+			const state = localService.stateManager.getSessionState(sessionResource.toString());
+			assert.strictEqual(state?.chats.find(c => c.resource === defaultChatUri)?.title, 'Renamed Default Chat');
+		});
+
 		test('restoreSession preserves peer chat catalog order regardless of load timing', async () => {
 			class MultiChatAgent extends MockAgent {
 				async createChat(_session: URI, _chat: URI): Promise<void> { }

src/vs/sessions/contrib/providers/agentHost/AGENT_HOST_SESSIONS_PROVIDER.md

@@ -141,7 +141,8 @@ When restoring Copilot SDK history, `mapSessionEvents` best-effort reconstructs
 ## CRUD & Stubbed Operations
 
 - `archiveSession` / `unarchiveSession` / `deleteSession` — round-trip to the backend. `deleteSessions` is the batch variant (used when multiple sessions are selected): it disposes each backend session and emits a single removal change event. Sessions advertise `capabilities.supportsDelete`, so the shared sessions-list "Delete..." action (contributed by the sessions workbench, gated on `SessionSupportsDeleteContext`) confirms and invokes deletion — there is no provider-specific delete action.
-- `renameChat` — updates the session title.
+- `renameChat` — renames a single chat independently of the session title. For an additional peer chat it dispatches `SessionTitleChanged` on that chat's channel; for the default/main chat it dispatches on the default chat channel (`setDefaultChatTitle`). The host persists the new title under `customChatTitle:<chatUri>` and re-applies it on restore — the default chat's title is seeded back through `restoreSession`/`_ensureDefaultChat`, peer chats through `_restorePeerChats` — so an independently-renamed main/peer chat survives a process restart or idle eviction instead of reverting to the session title.
+- `renameSession` — updates the session-level title.
 - `deleteChat` — no-op (agent host sessions don't model individually deletable chats).
 - `forkChat(sessionId, sourceChat, turnId)` — multi-chat only. Mints a peer chat URI and calls `connection.createChat(sessionUri, chatUri, { fork: { source, turnId } })`, where `source` is the backend chat URI (a `chatId` fragment addresses a peer chat, otherwise the session's default chat). The host seeds the new chat with the forked history; the provider waits for it to surface in `cached.chats` and returns it. Routed from the **Fork Conversation** gesture via `ISessionsManagementService.forkChatInSession`; single-chat sessions instead fork into a new session (the workbench `AgentHostSessionHandler.forkSession`).