agentHost: defer interactive MCP client registration

Keep automatic MCP authentication probes non-interactive so unsupported dynamic client registration is only surfaced after the user chooses Authenticate.

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

.github/skills/sessions/SKILL.md

@@ -77,6 +77,7 @@ Then read the relevant spec for the area you are changing (see table below). If
 - **Every untitled-session-title fallback must be quick-chat aware**: an untitled session's title observable is `''`, so a hardcoded `localize(…, "New Session")` fallback shows "New Session" even for a quick chat (whose composer says "New Chat"). Route **all** such fallbacks through the shared `getUntitledSessionTitle(isQuickChat)` helper (`services/sessions/common/session.ts`, boolean param so each caller controls reader-tracked `.read(reader)` vs `.get()`). There are ≥5 sites — titlebar (`sessionsTitleBarWidget`), session header (×2: title + rename placeholder), list-row hover (`sessionHoverContent`), sessions picker (`sessionsActions`) — keep them on the helper; never hardcode "New Session". (The Cmd+N *action* title stays "New Session" — that action creates a session, unrelated to a session's own title.)
 - **`NeedsInput` is still an active turn for live turn UI**: agent-host tool and input confirmations intentionally transition a running chat from `InProgress` to `NeedsInput` without ending `activeTurn`. Live status surfaces such as the chat input pills must use `isActiveSessionStatus` so they do not disappear until the next output returns the chat to `InProgress`.
 - **Agent-host-only exclusions for built-in client tools belong in `ClientToolSetsContribution`, not the global tool registration**: `AgentHostActiveClientService.getClientTools` advertises enabled members of every non-deprecated tool set, including extension-contributed sets. Omit an unsupported built-in tool from the client tool sets so normal Copilot chat can continue using it; do not treat this contribution as the sole Agent Host allowlist.
+- **Non-interactive MCP authentication probes must not create dynamic authentication providers**: Provider creation can prompt for manual client registration when dynamic registration is unsupported. With `allowInteraction: false`, only inspect existing providers and sessions; defer metadata discovery and provider creation until the user invokes the `mcpAuthenticationRequired` action.
 
 ## Capturing Feedback (meta-rule)
 

src/vs/workbench/contrib/chat/browser/agentSessions/agentHost/agentHostAuth.ts

@@ -279,7 +279,7 @@ export async function resolveMcpServerAuthentication(
 	const scopes = options.scopes;
 	for (const authorizationServer of protectedResource.authorization_servers ?? []) {
 		const authorizationServerUri = URI.parse(authorizationServer);
-		const providerId = await getOrCreateProviderForMcpResource(authorizationServerUri, protectedResource, authenticationService, logService, options.logPrefix);
+		const providerId = await getOrCreateProviderForMcpResource(authorizationServerUri, protectedResource, authenticationService, logService, options.logPrefix, options.allowInteraction);
 		if (!providerId) {
 			continue;
 		}
@@ -317,10 +317,11 @@ async function getOrCreateProviderForMcpResource(
 	authenticationService: IAuthenticationService,
 	logService: ILogService,
 	logPrefix: string,
+	allowCreation: boolean,
 ): Promise<string | undefined> {
 	const resourceUri = URI.parse(protectedResource.resource);
 	const existing = await authenticationService.getOrActivateProviderIdForServer(authorizationServer, resourceUri);
-	if (existing) {
+	if (existing || !allowCreation) {
 		return existing;
 	}
 

src/vs/workbench/contrib/chat/test/browser/agentSessions/agentHostAuth.test.ts

@@ -237,6 +237,41 @@ suite('resolveMcpServerAuthentication', () => {
 			requestedScopes: [['notifications']],
 		});
 	});
+
+	test('does not attempt dynamic provider creation without user interaction', async () => {
+		const warnings: string[] = [];
+		const logService = new class extends NullLogService {
+			override warn(message: string): void {
+				warnings.push(message);
+			}
+		}();
+		const instantiationService = disposables.add(new TestInstantiationService());
+		instantiationService.stub(IAuthenticationService, createMockAuthService({}));
+		instantiationService.stub(IAuthenticationMcpAccessService, {});
+		instantiationService.stub(IAuthenticationMcpService, {
+			getAccountPreference: () => undefined,
+		});
+		instantiationService.stub(IAuthenticationMcpUsageService, {});
+		instantiationService.stub(ILogService, logService);
+
+		const result = await instantiationService.invokeFunction(resolveMcpServerAuthentication, {
+			resource: 'https://mcp.example.com',
+			authorization_servers: ['not-a-valid-authorization-server'],
+		}, {
+			allowInteraction: false,
+			logPrefix: '[AgentHost]',
+			mcpServerId: 'server-id',
+			mcpServerName: 'Example',
+			mcpServerUrl: 'https://mcp.example.com',
+			scopes: [],
+			authenticate: async () => { },
+		});
+
+		assert.deepStrictEqual({ result, warnings }, {
+			result: false,
+			warnings: [],
+		});
+	});
 });
 
 suite('authenticateProtectedResources', () => {