Enable BYOK in air-gapped scenarios/without GitHub auth

[dmitrivMS]

Air-gapped BYOK: enable chat and some other AI functionality when user is not authenticated (with or without utility models enabled).

Fixes #246551
Fixes #275591
Fixes #313461
Fixes #272843

Related #294708

Fixes https://github.com/microsoft/vscode-internalbacklog/issues/7044

Related https://github.com/microsoft/vscode-internalbacklog/issues/5892

[Copilot]

Pull request overview

This PR updates VS Code’s Copilot Chat integration to better support BYOK (bring-your-own-key) usage in air‑gapped / signed-out scenarios by avoiding hard dependencies on GitHub authentication for parts of the extension that don’t strictly require it.

Changes:

• Adjusts sign-in UI surfacing and welcome messaging so BYOK availability suppresses GitHub-auth-specific warnings.
• Adds “no GitHub auth” guards/fallbacks in Copilot extension components (model metadata fetch, embeddings, prompt JSON rendering).
• Changes conversation feature activation logic to allow activation when non-Copilot (BYOK) chat models are present.

Show a summary per file

File	Description
src/vs/workbench/contrib/chat/browser/chatSetup/chatSetupContributions.ts	Tweaks Accounts menu sign-in action label/visibility logic.
extensions/copilot/src/platform/endpoint/node/modelMetadataFetcher.ts	Stops model metadata fetch when Copilot token acquisition fails (BYOK-only).
extensions/copilot/src/platform/embeddings/common/remoteEmbeddingsComputer.ts	Adds early auth guard for remote embeddings requests.
extensions/copilot/src/extension/prompts/node/base/promptRenderer.ts	Falls back to a stub endpoint when utility model resolution fails during JSON rendering.
extensions/copilot/src/extension/prompt/node/chatMLFetcher.ts	Loosens Copilot token dependency for BYOK endpoints (but see comments).
extensions/copilot/src/extension/conversation/vscode-node/languageModelAccess.ts	Prevents registering LM/embeddings features without a GitHub session.
extensions/copilot/src/extension/conversation/vscode-node/conversationFeature.ts	Activates conversation features based on BYOK model presence; adds auth gating for search providers (but contains issues).
extensions/copilot/src/extension/conversation/vscode-node/chatParticipants.ts	Avoids resolving the utility endpoint unless a quota fallback is needed.
extensions/copilot/src/extension/chatSessions/copilotcli/node/copilotCli.ts	Skips CLI model fetch without a GitHub session.
extensions/copilot/src/extension/authentication/vscode-node/authentication.contribution.ts	Alters permissive-auth upgrade flow behavior when signed out.
extensions/copilot/package.json	Hides Copilot auth-related welcome messages when BYOK models are present.

Copilot's findings

Comments suppressed due to low confidence (1)

extensions/copilot/src/extension/conversation/vscode-node/conversationFeature.ts:222

• Same typo here: anyGithubSession should be anyGitHubSession to match the authentication service API and avoid a compile error.

		// Don't register for no auth user or or BYOK-only users
		if (!this.authenticationService.anyGithubSession || this.authenticationService.copilotToken?.isNoAuthUser) {
			this.logService.debug('ConversationFeature: Skipping settings search provider registration - no GitHub session available');
			return;

• Files reviewed: 11/11 changed files
• Comments generated: 6

[Copilot]

Copilot's findings

• Files reviewed: 20/20 changed files
• Comments generated: 2

[Copilot]

Copilot's findings

Comments suppressed due to low confidence (2)

extensions/copilot/src/extension/conversation/vscode-node/conversationFeature.ts:199

• In BYOK-only mode, registerSearchProvider() sets _searchProviderRegistered = true before checking for a GitHub session and then returns early. If the user later signs in, the provider will never register because the flag blocks future attempts and activation doesn’t re-run. Consider only setting _searchProviderRegistered after successful registration, or re-attempting registration when auth becomes available (and/or clearing the flag on auth change).

This issue also appears on line 208 of the same file.

	private registerSearchProvider(): IDisposable | undefined {
		if (this._searchProviderRegistered) {
			return;
		} else {
			this._searchProviderRegistered = true;

			// Don't register for no auth user or BYOK-only users
			if (!this.authenticationService.anyGitHubSession || this.authenticationService.copilotToken?.isNoAuthUser) {
				this.logService.debug('ConversationFeature: Skipping search provider registration - no GitHub session available');
				return;
			}

extensions/copilot/src/extension/conversation/vscode-node/conversationFeature.ts:220

• Same issue as registerSearchProvider(): _settingsSearchProviderRegistered is set before the GitHub-session guard and can prevent later registration when the feature was activated via BYOK first and the user signs in afterwards. Defer setting the flag until after registration succeeds, or re-run registration on auth/session changes.

	private registerSettingsSearchProvider(): IDisposable | undefined {
		if (this._settingsSearchProviderRegistered) {
			return;
		}

		this._settingsSearchProviderRegistered = true;

		// Don't register for no auth user or or BYOK-only users
		if (!this.authenticationService.anyGitHubSession || this.authenticationService.copilotToken?.isNoAuthUser) {
			this.logService.debug('ConversationFeature: Skipping settings search provider registration - no GitHub session available');
			return;
		}

• Files reviewed: 21/21 changed files
• Comments generated: 2

[github-actions]

Base: 827fd6c6 Current: 96ab5ab3

No screenshot changes.