Add support for GH Custom Agents (#278251)

src/vs/workbench/api/browser/mainThreadChatAgents2.ts

@@ -26,6 +26,7 @@ import { IUriIdentityService } from '../../../platform/uriIdentity/common/uriIde
 import { IChatWidgetService } from '../../contrib/chat/browser/chat.js';
 import { AddDynamicVariableAction, IAddDynamicVariableContext } from '../../contrib/chat/browser/contrib/chatDynamicVariables.js';
 import { IChatAgentHistoryEntry, IChatAgentImplementation, IChatAgentRequest, IChatAgentService } from '../../contrib/chat/common/chatAgents.js';
+import { ICustomAgentQueryOptions, IPromptsService } from '../../contrib/chat/common/promptSyntax/service/promptsService.js';
 import { IChatEditingService, IChatRelatedFileProviderMetadata } from '../../contrib/chat/common/chatEditingService.js';
 import { IChatModel } from '../../contrib/chat/common/chatModel.js';
 import { ChatRequestAgentPart } from '../../contrib/chat/common/chatParserTypes.js';
@@ -96,6 +97,9 @@ export class MainThreadChatAgents2 extends Disposable implements MainThreadChatA
 
 	private readonly _chatRelatedFilesProviders = this._register(new DisposableMap<number, IDisposable>());
 
+	private readonly _customAgentsProviders = this._register(new DisposableMap<number, IDisposable>());
+	private readonly _customAgentsProviderEmitters = this._register(new DisposableMap<number, Emitter<void>>());
+
 	private readonly _pendingProgress = new Map<string, { progress: (parts: IChatProgress[]) => void; chatSession: IChatModel | undefined }>();
 	private readonly _proxy: ExtHostChatAgentsShape2;
 
@@ -115,6 +119,7 @@ export class MainThreadChatAgents2 extends Disposable implements MainThreadChatA
 		@ILogService private readonly _logService: ILogService,
 		@IExtensionService private readonly _extensionService: IExtensionService,
 		@IUriIdentityService private readonly _uriIdentityService: IUriIdentityService,
+		@IPromptsService private readonly _promptsService: IPromptsService,
 	) {
 		super();
 		this._proxy = extHostContext.getProxy(ExtHostContext.ExtHostChatAgents2);
@@ -427,6 +432,46 @@ export class MainThreadChatAgents2 extends Disposable implements MainThreadChatA
 	$unregisterRelatedFilesProvider(handle: number): void {
 		this._chatRelatedFilesProviders.deleteAndDispose(handle);
 	}
+
+	async $registerCustomAgentsProvider(handle: number, extensionId: ExtensionIdentifier): Promise<void> {
+		const extension = await this._extensionService.getExtension(extensionId.value);
+		if (!extension) {
+			this._logService.error(`[MainThreadChatAgents2] Could not find extension for CustomAgentsProvider: ${extensionId.value}`);
+			return;
+		}
+
+		const emitter = new Emitter<void>();
+		this._customAgentsProviderEmitters.set(handle, emitter);
+
+		const disposable = this._promptsService.registerCustomAgentsProvider(extension, {
+			onDidChangeCustomAgents: emitter.event,
+			provideCustomAgents: async (options: ICustomAgentQueryOptions, token: CancellationToken) => {
+				const agents = await this._proxy.$provideCustomAgents(handle, options, token);
+				if (!agents) {
+					return undefined;
+				}
+				// Convert UriComponents to URI
+				return agents.map(agent => ({
+					...agent,
+					uri: URI.revive(agent.uri)
+				}));
+			}
+		});
+
+		this._customAgentsProviders.set(handle, disposable);
+	}
+
+	$unregisterCustomAgentsProvider(handle: number): void {
+		this._customAgentsProviders.deleteAndDispose(handle);
+		this._customAgentsProviderEmitters.deleteAndDispose(handle);
+	}
+
+	$onDidChangeCustomAgents(handle: number): void {
+		const emitter = this._customAgentsProviderEmitters.get(handle);
+		if (emitter) {
+			emitter.fire();
+		}
+	}
 }
 
 

src/vs/workbench/api/common/extHost.api.impl.ts

@@ -1541,6 +1541,10 @@ export function createApiFactoryAndRegisterActors(accessor: ServicesAccessor): I
 				checkProposedApiEnabled(extension, 'chatContextProvider');
 				return extHostChatContext.registerChatContextProvider(selector ? checkSelector(selector) : undefined, `${extension.id}-${id}`, provider);
 			},
+			registerCustomAgentsProvider(provider: vscode.CustomAgentsProvider): vscode.Disposable {
+				checkProposedApiEnabled(extension, 'chatParticipantPrivate');
+				return extHostChatAgents2.registerCustomAgentsProvider(extension, provider);
+			},
 		};
 
 		// namespace: lm
@@ -1942,7 +1946,8 @@ export function createApiFactoryAndRegisterActors(accessor: ServicesAccessor): I
 			McpStdioServerDefinition: extHostTypes.McpStdioServerDefinition,
 			McpStdioServerDefinition2: extHostTypes.McpStdioServerDefinition,
 			McpToolAvailability: extHostTypes.McpToolAvailability,
-			SettingsSearchResultKind: extHostTypes.SettingsSearchResultKind
+			SettingsSearchResultKind: extHostTypes.SettingsSearchResultKind,
+			CustomAgentTarget: extHostTypes.CustomAgentTarget,
 		};
 	};
 }

src/vs/workbench/api/common/extHost.protocol.ts

@@ -65,6 +65,7 @@ import { IChatRequestVariableValue } from '../../contrib/chat/common/chatVariabl
 import { ChatAgentLocation } from '../../contrib/chat/common/constants.js';
 import { IChatMessage, IChatResponsePart, ILanguageModelChatMetadataAndIdentifier, ILanguageModelChatSelector } from '../../contrib/chat/common/languageModels.js';
 import { IPreparedToolInvocation, IToolInvocation, IToolInvocationPreparationContext, IToolProgressStep, IToolResult, ToolDataSource } from '../../contrib/chat/common/languageModelToolsService.js';
+import { ICustomAgentQueryOptions, IExternalCustomAgent } from '../../contrib/chat/common/promptSyntax/service/promptsService.js';
 import { DebugConfigurationProviderTriggerKind, IAdapterDescriptor, IConfig, IDebugSessionReplMode, IDebugTestRunReference, IDebugVisualization, IDebugVisualizationContext, IDebugVisualizationTreeItem, MainThreadDebugVisualization } from '../../contrib/debug/common/debug.js';
 import { McpCollectionDefinition, McpConnectionState, McpServerDefinition, McpServerLaunch } from '../../contrib/mcp/common/mcpTypes.js';
 import * as notebookCommon from '../../contrib/notebook/common/notebookCommon.js';
@@ -1393,6 +1394,9 @@ export interface MainThreadChatAgentsShape2 extends IChatAgentProgressShape, IDi
 	$unregisterChatParticipantDetectionProvider(handle: number): void;
 	$registerRelatedFilesProvider(handle: number, metadata: IChatRelatedFilesProviderMetadata): void;
 	$unregisterRelatedFilesProvider(handle: number): void;
+	$registerCustomAgentsProvider(handle: number, extension: ExtensionIdentifier): void;
+	$unregisterCustomAgentsProvider(handle: number): void;
+	$onDidChangeCustomAgents(handle: number): void;
 	$registerAgentCompletionsProvider(handle: number, id: string, triggerCharacters: string[]): void;
 	$unregisterAgentCompletionsProvider(handle: number, id: string): void;
 	$updateAgent(handle: number, metadataUpdate: IExtensionChatAgentMetadata): void;
@@ -1457,6 +1461,7 @@ export interface ExtHostChatAgentsShape2 {
 	$releaseSession(sessionId: string): void;
 	$detectChatParticipant(handle: number, request: Dto<IChatAgentRequest>, context: { history: IChatAgentHistoryEntryDto[] }, options: { participants: IChatParticipantMetadata[]; location: ChatAgentLocation }, token: CancellationToken): Promise<IChatParticipantDetectionResult | null | undefined>;
 	$provideRelatedFiles(handle: number, request: Dto<IChatRequestDraft>, token: CancellationToken): Promise<Dto<IChatRelatedFile>[] | undefined>;
+	$provideCustomAgents(handle: number, options: ICustomAgentQueryOptions, token: CancellationToken): Promise<Dto<IExternalCustomAgent>[] | undefined>;
 	$setRequestTools(requestId: string, tools: UserSelectedTools): void;
 }
 export interface IChatParticipantMetadata {

src/vs/workbench/api/common/extHostChatAgents2.ts

@@ -34,6 +34,7 @@ import { ExtHostLanguageModels } from './extHostLanguageModels.js';
 import { ExtHostLanguageModelTools } from './extHostLanguageModelTools.js';
 import * as typeConvert from './extHostTypeConverters.js';
 import * as extHostTypes from './extHostTypes.js';
+import { ICustomAgentQueryOptions, IExternalCustomAgent } from '../../contrib/chat/common/promptSyntax/service/promptsService.js';
 
 export class ChatAgentResponseStream {
 
@@ -395,6 +396,9 @@ export class ExtHostChatAgents2 extends Disposable implements ExtHostChatAgentsS
 	private static _relatedFilesProviderIdPool = 0;
 	private readonly _relatedFilesProviders = new Map<number, ExtHostRelatedFilesProvider>();
 
+	private static _customAgentsProviderIdPool = 0;
+	private readonly _customAgentsProviders = new Map<number, { extension: IExtensionDescription; provider: vscode.CustomAgentsProvider }>();
+
 	private readonly _sessionDisposables: DisposableMap<string, DisposableStore> = this._register(new DisposableMap());
 	private readonly _completionDisposables: DisposableMap<number, DisposableStore> = this._register(new DisposableMap());
 
@@ -472,6 +476,28 @@ export class ExtHostChatAgents2 extends Disposable implements ExtHostChatAgentsS
 		});
 	}
 
+	registerCustomAgentsProvider(extension: IExtensionDescription, provider: vscode.CustomAgentsProvider): vscode.Disposable {
+		const handle = ExtHostChatAgents2._customAgentsProviderIdPool++;
+		this._customAgentsProviders.set(handle, { extension, provider });
+		this._proxy.$registerCustomAgentsProvider(handle, extension.identifier);
+
+		const disposables = new DisposableStore();
+
+		// Listen to provider change events and notify main thread
+		if (provider.onDidChangeCustomAgents) {
+			disposables.add(provider.onDidChangeCustomAgents(() => {
+				this._proxy.$onDidChangeCustomAgents(handle);
+			}));
+		}
+
+		disposables.add(toDisposable(() => {
+			this._customAgentsProviders.delete(handle);
+			this._proxy.$unregisterCustomAgentsProvider(handle);
+		}));
+
+		return disposables;
+	}
+
 	async $provideRelatedFiles(handle: number, request: IChatRequestDraft, token: CancellationToken): Promise<Dto<IChatRelatedFile>[] | undefined> {
 		const provider = this._relatedFilesProviders.get(handle);
 		if (!provider) {
@@ -482,6 +508,15 @@ export class ExtHostChatAgents2 extends Disposable implements ExtHostChatAgentsS
 		return await provider.provider.provideRelatedFiles(extRequestDraft, token) ?? undefined;
 	}
 
+	async $provideCustomAgents(handle: number, options: ICustomAgentQueryOptions, token: CancellationToken): Promise<IExternalCustomAgent[] | undefined> {
+		const providerData = this._customAgentsProviders.get(handle);
+		if (!providerData) {
+			return Promise.resolve(undefined);
+		}
+
+		return await providerData.provider.provideCustomAgents(options, token) ?? undefined;
+	}
+
 	async $detectChatParticipant(handle: number, requestDto: Dto<IChatAgentRequest>, context: { history: IChatAgentHistoryEntryDto[] }, options: { location: ChatAgentLocation; participants?: vscode.ChatParticipantMetadata[] }, token: CancellationToken): Promise<vscode.ChatParticipantDetectionResult | null | undefined> {
 		const detector = this._participantDetectionProviders.get(handle);
 		if (!detector) {

src/vs/workbench/api/common/extHostTypes.ts

@@ -3492,6 +3492,11 @@ export enum ChatErrorLevel {
 	Error = 2
 }
 
+export enum CustomAgentTarget {
+	GitHubCopilot = 'github-copilot',
+	VSCode = 'vscode',
+}
+
 export class LanguageModelChatMessage implements vscode.LanguageModelChatMessage {
 
 	static User(content: string | (LanguageModelTextPart | LanguageModelToolResultPart | LanguageModelToolCallPart | LanguageModelDataPart)[], name?: string): LanguageModelChatMessage {

src/vs/workbench/contrib/chat/browser/modelPicker/modePickerActionItem.ts

@@ -27,7 +27,7 @@ import { IProductService } from '../../../../../platform/product/common/productS
 import { IChatAgentService } from '../../common/chatAgents.js';
 import { ChatMode, IChatMode, IChatModeService } from '../../common/chatModes.js';
 import { ChatAgentLocation, ChatConfiguration, ChatModeKind } from '../../common/constants.js';
-import { PromptsStorage } from '../../common/promptSyntax/service/promptsService.js';
+import { ExtensionAgentSourceType, PromptsStorage } from '../../common/promptSyntax/service/promptsService.js';
 import { getOpenChatActionIdForMode } from '../actions/chatActions.js';
 import { IToggleChatModeArgs, ToggleAgentModeActionId } from '../actions/chatExecuteActions.js';
 
@@ -104,7 +104,7 @@ export class ModePickerActionItem extends ActionWidgetDropdownActionViewItem {
 				const otherBuiltinModes = modes.builtin.filter(mode => mode.id !== ChatMode.Agent.id);
 				const customModes = groupBy(
 					modes.custom,
-					mode => mode.source?.storage === PromptsStorage.extension && mode.source.extensionId.value === productService.defaultChatAgent?.chatExtensionId ?
+					mode => mode.source?.storage === PromptsStorage.extension && mode.source.extensionId.value === productService.defaultChatAgent?.chatExtensionId && mode.source.type === ExtensionAgentSourceType.contribution ?
 						'builtin' : 'custom');
 
 				const customBuiltinModeActions = customModes.builtin?.map(mode => {

src/vs/workbench/contrib/chat/common/chatModes.ts

@@ -20,7 +20,7 @@ import { IChatAgentService } from './chatAgents.js';
 import { ChatContextKeys } from './chatContextKeys.js';
 import { ChatConfiguration, ChatModeKind } from './constants.js';
 import { IHandOff } from './promptSyntax/promptFileParser.js';
-import { IAgentSource, ICustomAgent, IPromptsService, PromptsStorage } from './promptSyntax/service/promptsService.js';
+import { ExtensionAgentSourceType, IAgentSource, ICustomAgent, IPromptsService, PromptsStorage } from './promptSyntax/service/promptsService.js';
 
 export const IChatModeService = createDecorator<IChatModeService>('chatModeService');
 export interface IChatModeService {
@@ -419,7 +419,7 @@ export class CustomChatMode implements IChatMode {
 }
 
 type IChatModeSourceData =
-	| { readonly storage: PromptsStorage.extension; readonly extensionId: string }
+	| { readonly storage: PromptsStorage.extension; readonly extensionId: string; type?: ExtensionAgentSourceType }
 	| { readonly storage: PromptsStorage.local | PromptsStorage.user };
 
 function isChatModeSourceData(value: unknown): value is IChatModeSourceData {
@@ -438,7 +438,7 @@ function serializeChatModeSource(source: IAgentSource | undefined): IChatModeSou
 		return undefined;
 	}
 	if (source.storage === PromptsStorage.extension) {
-		return { storage: PromptsStorage.extension, extensionId: source.extensionId.value };
+		return { storage: PromptsStorage.extension, extensionId: source.extensionId.value, type: source.type };
 	}
 	return { storage: source.storage };
 }
@@ -448,7 +448,7 @@ function reviveChatModeSource(data: IChatModeSourceData | undefined): IAgentSour
 		return undefined;
 	}
 	if (data.storage === PromptsStorage.extension) {
-		return { storage: PromptsStorage.extension, extensionId: new ExtensionIdentifier(data.extensionId) };
+		return { storage: PromptsStorage.extension, extensionId: new ExtensionIdentifier(data.extensionId), type: data.type ?? ExtensionAgentSourceType.contribution };
 	}
 	return { storage: data.storage };
 }

src/vs/workbench/contrib/chat/common/promptSyntax/service/promptsService.ts

@@ -15,6 +15,44 @@ import { PromptsType } from '../promptTypes.js';
 import { IHandOff, ParsedPromptFile } from '../promptFileParser.js';
 import { ResourceSet } from '../../../../../../base/common/map.js';
 
+/**
+ * Target environment for custom agents.
+ */
+export enum CustomAgentTarget {
+	GitHubCopilot = 'github-copilot',
+	VSCode = 'vscode',
+}
+
+/**
+ * Options for querying custom agents.
+ */
+export interface ICustomAgentQueryOptions {
+	/**
+	 * Filter agents by target environment.
+	 */
+	readonly target?: CustomAgentTarget;
+}
+
+/**
+ * Represents a custom agent resource from an external provider.
+ */
+export interface IExternalCustomAgent {
+	/**
+	 * The unique identifier/name of the custom agent resource.
+	 */
+	readonly name: string;
+
+	/**
+	 * A description of what the custom agent resource does.
+	 */
+	readonly description: string;
+
+	/**
+	 * The URI to the agent or prompt resource file.
+	 */
+	readonly uri: URI;
+}
+
 /**
  * Provides prompt services.
  */
@@ -29,6 +67,14 @@ export enum PromptsStorage {
 	extension = 'extension'
 }
 
+/**
+ * The type of source for extension agents.
+ */
+export enum ExtensionAgentSourceType {
+	contribution = 'contribution',
+	provider = 'provider',
+}
+
 /**
  * Represents a prompt path with its type.
  * This is used for both prompt files and prompt source folders.
@@ -67,6 +113,7 @@ export interface IExtensionPromptPath extends IPromptPathBase {
 	readonly extension: IExtensionDescription;
 	readonly name: string;
 	readonly description: string;
+	readonly source: ExtensionAgentSourceType;
 }
 export interface ILocalPromptPath extends IPromptPathBase {
 	readonly storage: PromptsStorage.local;
@@ -78,6 +125,7 @@ export interface IUserPromptPath extends IPromptPathBase {
 export type IAgentSource = {
 	readonly storage: PromptsStorage.extension;
 	readonly extensionId: ExtensionIdentifier;
+	readonly type: ExtensionAgentSourceType;
 } | {
 	readonly storage: PromptsStorage.local | PromptsStorage.user;
 };
@@ -270,6 +318,18 @@ export interface IPromptsService extends IDisposable {
 	 */
 	setDisabledPromptFiles(type: PromptsType, uris: ResourceSet): void;
 
+	/**
+	 * Registers a CustomAgentsProvider that can provide custom agents for repositories.
+	 * This is part of the proposed API and requires the chatParticipantPrivate proposal.
+	 * @param extension The extension registering the provider.
+	 * @param provider The provider implementation with optional change event.
+	 * @returns A disposable that unregisters the provider when disposed.
+	 */
+	registerCustomAgentsProvider(extension: IExtensionDescription, provider: {
+		onDidChangeCustomAgents?: Event<void>;
+		provideCustomAgents: (options: ICustomAgentQueryOptions, token: CancellationToken) => Promise<IExternalCustomAgent[] | undefined>;
+	}): IDisposable;
+
 	/**
 	 * Gets list of claude skills files.
 	 */

src/vs/workbench/contrib/chat/common/promptSyntax/service/promptsServiceImpl.ts

@@ -6,7 +6,7 @@
 import { CancellationToken } from '../../../../../../base/common/cancellation.js';
 import { CancellationError } from '../../../../../../base/common/errors.js';
 import { Emitter, Event } from '../../../../../../base/common/event.js';
-import { Disposable, IDisposable } from '../../../../../../base/common/lifecycle.js';
+import { Disposable, DisposableStore, IDisposable } from '../../../../../../base/common/lifecycle.js';
 import { ResourceMap, ResourceSet } from '../../../../../../base/common/map.js';
 import { dirname, isEqual } from '../../../../../../base/common/resources.js';
 import { URI } from '../../../../../../base/common/uri.js';
@@ -17,6 +17,7 @@ import { localize } from '../../../../../../nls.js';
 import { IConfigurationService } from '../../../../../../platform/configuration/common/configuration.js';
 import { IExtensionDescription } from '../../../../../../platform/extensions/common/extensions.js';
 import { IFileService } from '../../../../../../platform/files/common/files.js';
+import { IExtensionService } from '../../../../../services/extensions/common/extensions.js';
 import { IInstantiationService } from '../../../../../../platform/instantiation/common/instantiation.js';
 import { ILabelService } from '../../../../../../platform/label/common/label.js';
 import { ILogService } from '../../../../../../platform/log/common/log.js';
@@ -29,10 +30,9 @@ import { getCleanPromptName } from '../config/promptFileLocations.js';
 import { PROMPT_LANGUAGE_ID, PromptsType, getPromptsTypeForLanguageId } from '../promptTypes.js';
 import { PromptFilesLocator } from '../utils/promptFilesLocator.js';
 import { PromptFileParser, ParsedPromptFile, PromptHeaderAttributes } from '../promptFileParser.js';
-import { IAgentInstructions, IAgentSource, IChatPromptSlashCommand, ICustomAgent, IExtensionPromptPath, ILocalPromptPath, IPromptPath, IPromptsService, IClaudeSkill, IUserPromptPath, PromptsStorage } from './promptsService.js';
+import { IAgentInstructions, IAgentSource, IChatPromptSlashCommand, ICustomAgent, IExtensionPromptPath, ILocalPromptPath, IPromptPath, IPromptsService, IClaudeSkill, IUserPromptPath, PromptsStorage, ICustomAgentQueryOptions, IExternalCustomAgent, ExtensionAgentSourceType } from './promptsService.js';
 import { Delayer } from '../../../../../../base/common/async.js';
 import { Schemas } from '../../../../../../base/common/network.js';
-import { IExtensionService } from '../../../../../services/extensions/common/extensions.js';
 
 /**
  * Provides prompt services.
@@ -154,16 +154,107 @@ export class PromptsService extends Disposable implements IPromptsService {
 		const prompts = await Promise.all([
 			this.fileLocator.listFiles(type, PromptsStorage.user, token).then(uris => uris.map(uri => ({ uri, storage: PromptsStorage.user, type } satisfies IUserPromptPath))),
 			this.fileLocator.listFiles(type, PromptsStorage.local, token).then(uris => uris.map(uri => ({ uri, storage: PromptsStorage.local, type } satisfies ILocalPromptPath))),
-			this.getExtensionContributions(type)
+			this.getExtensionPromptFiles(type, token),
 		]);
 
 		return [...prompts.flat()];
 	}
 
+	/**
+	 * Registry of CustomAgentsProvider instances. Extensions can register providers via the proposed API.
+	 */
+	private readonly customAgentsProviders: Array<{
+		extension: IExtensionDescription;
+		onDidChangeCustomAgents?: Event<void>;
+		provideCustomAgents: (options: ICustomAgentQueryOptions, token: CancellationToken) => Promise<IExternalCustomAgent[] | undefined>;
+	}> = [];
+
+	/**
+	 * Registers a CustomAgentsProvider. This will be called by the extension host bridge when
+	 * an extension registers a provider via vscode.chat.registerCustomAgentsProvider().
+	 */
+	public registerCustomAgentsProvider(extension: IExtensionDescription, provider: {
+		onDidChangeCustomAgents?: Event<void>;
+		provideCustomAgents: (options: ICustomAgentQueryOptions, token: CancellationToken) => Promise<IExternalCustomAgent[] | undefined>;
+	}): IDisposable {
+		const providerEntry = { extension, ...provider };
+		this.customAgentsProviders.push(providerEntry);
+
+		const disposables = new DisposableStore();
+
+		// Listen to provider change events to rerun computeListPromptFiles
+		if (provider.onDidChangeCustomAgents) {
+			disposables.add(provider.onDidChangeCustomAgents(() => {
+				this.cachedFileLocations[PromptsType.agent] = undefined;
+				this.cachedCustomAgents.refresh();
+			}));
+		}
+
+		// Invalidate agent cache when providers change
+		this.cachedFileLocations[PromptsType.agent] = undefined;
+		this.cachedCustomAgents.refresh();
+
+		disposables.add({
+			dispose: () => {
+				const index = this.customAgentsProviders.findIndex((p) => p === providerEntry);
+				if (index >= 0) {
+					this.customAgentsProviders.splice(index, 1);
+					this.cachedFileLocations[PromptsType.agent] = undefined;
+					this.cachedCustomAgents.refresh();
+				}
+			}
+		});
+
+		return disposables;
+	}
+
+	private async listCustomAgentsFromProvider(token: CancellationToken): Promise<IPromptPath[]> {
+		const result: IPromptPath[] = [];
+
+		if (this.customAgentsProviders.length === 0) {
+			return result;
+		}
+
+		// Collect agents from all providers
+		for (const providerEntry of this.customAgentsProviders) {
+			try {
+				const agents = await providerEntry.provideCustomAgents({}, token);
+				if (!agents || token.isCancellationRequested) {
+					continue;
+				}
+
+				for (const agent of agents) {
+					try {
+						await this.filesConfigService.updateReadonly(agent.uri, true);
+					} catch (e) {
+						const msg = e instanceof Error ? e.message : String(e);
+						this.logger.error(`[listCustomAgentsFromProvider] Failed to make agent file readonly: ${agent.uri}`, msg);
+					}
+
+					result.push({
+						uri: agent.uri,
+						name: agent.name,
+						description: agent.description,
+						storage: PromptsStorage.extension,
+						type: PromptsType.agent,
+						extension: providerEntry.extension,
+						source: ExtensionAgentSourceType.provider
+					} satisfies IExtensionPromptPath);
+				}
+			} catch (e) {
+				this.logger.error(`[listCustomAgentsFromProvider] Failed to get custom agents from provider`, e instanceof Error ? e.message : String(e));
+			}
+		}
+
+		return result;
+	}
+
+
+
 	public async listPromptFilesForStorage(type: PromptsType, storage: PromptsStorage, token: CancellationToken): Promise<readonly IPromptPath[]> {
 		switch (storage) {
 			case PromptsStorage.extension:
-				return this.getExtensionContributions(type);
+				return this.getExtensionPromptFiles(type, token);
 			case PromptsStorage.local:
 				return this.fileLocator.listFiles(type, PromptsStorage.local, token).then(uris => uris.map(uri => ({ uri, storage: PromptsStorage.local, type } satisfies ILocalPromptPath)));
 			case PromptsStorage.user:
@@ -173,9 +264,14 @@ export class PromptsService extends Disposable implements IPromptsService {
 		}
 	}
 
-	private async getExtensionContributions(type: PromptsType): Promise<IPromptPath[]> {
+	private async getExtensionPromptFiles(type: PromptsType, token: CancellationToken): Promise<IPromptPath[]> {
 		await this.extensionService.whenInstalledExtensionsRegistered();
-		return Promise.all(this.contributedFiles[type].values());
+		const contributedFiles = await Promise.all(this.contributedFiles[type].values());
+		if (type === PromptsType.agent) {
+			const providerAgents = await this.listCustomAgentsFromProvider(token);
+			return [...contributedFiles, ...providerAgents];
+		}
+		return contributedFiles;
 	}
 
 	public getSourceFolders(type: PromptsType): readonly IPromptPath[] {
@@ -359,7 +455,7 @@ export class PromptsService extends Disposable implements IPromptsService {
 				const msg = e instanceof Error ? e.message : String(e);
 				this.logger.error(`[registerContributedFile] Failed to make prompt file readonly: ${uri}`, msg);
 			}
-			return { uri, name, description, storage: PromptsStorage.extension, type, extension } satisfies IExtensionPromptPath;
+			return { uri, name, description, storage: PromptsStorage.extension, type, extension, source: ExtensionAgentSourceType.contribution } satisfies IExtensionPromptPath;
 		})();
 		bucket.set(uri, entryPromise);
 
@@ -578,7 +674,8 @@ namespace IAgentSource {
 		if (promptPath.storage === PromptsStorage.extension) {
 			return {
 				storage: PromptsStorage.extension,
-				extensionId: promptPath.extension.identifier
+				extensionId: promptPath.extension.identifier,
+				type: promptPath.source
 			};
 		} else {
 			return {

src/vs/workbench/contrib/chat/test/common/mockPromptsService.ts

@@ -11,7 +11,7 @@ import { ITextModel } from '../../../../../editor/common/model.js';
 import { IExtensionDescription } from '../../../../../platform/extensions/common/extensions.js';
 import { PromptsType } from '../../common/promptSyntax/promptTypes.js';
 import { ParsedPromptFile } from '../../common/promptSyntax/promptFileParser.js';
-import { IClaudeSkill, ICustomAgent, IPromptPath, IPromptsService, PromptsStorage } from '../../common/promptSyntax/service/promptsService.js';
+import { IClaudeSkill, ICustomAgent, ICustomAgentQueryOptions, IExternalCustomAgent, IPromptPath, IPromptsService, PromptsStorage } from '../../common/promptSyntax/service/promptsService.js';
 import { ResourceSet } from '../../../../../base/common/map.js';
 
 export class MockPromptsService implements IPromptsService {
@@ -53,6 +53,7 @@ export class MockPromptsService implements IPromptsService {
 	getAgentFileURIFromModeFile(oldURI: URI): URI | undefined { throw new Error('Not implemented'); }
 	getDisabledPromptFiles(type: PromptsType): ResourceSet { throw new Error('Method not implemented.'); }
 	setDisabledPromptFiles(type: PromptsType, uris: ResourceSet): void { throw new Error('Method not implemented.'); }
+	registerCustomAgentsProvider(extension: IExtensionDescription, provider: { provideCustomAgents: (options: ICustomAgentQueryOptions, token: CancellationToken) => Promise<IExternalCustomAgent[] | undefined> }): IDisposable { throw new Error('Method not implemented.'); }
 	findClaudeSkills(token: CancellationToken): Promise<IClaudeSkill[] | undefined> { throw new Error('Method not implemented.'); }
 	dispose(): void { }
 }

src/vs/workbench/contrib/chat/test/common/promptSyntax/service/promptsService.test.ts

@@ -36,7 +36,7 @@ import { ComputeAutomaticInstructions, newInstructionsCollectionEvent } from '..
 import { PromptsConfig } from '../../../../common/promptSyntax/config/config.js';
 import { INSTRUCTION_FILE_EXTENSION, INSTRUCTIONS_DEFAULT_SOURCE_FOLDER, LEGACY_MODE_DEFAULT_SOURCE_FOLDER, PROMPT_DEFAULT_SOURCE_FOLDER, PROMPT_FILE_EXTENSION } from '../../../../common/promptSyntax/config/promptFileLocations.js';
 import { INSTRUCTIONS_LANGUAGE_ID, PROMPT_LANGUAGE_ID, PromptsType } from '../../../../common/promptSyntax/promptTypes.js';
-import { ICustomAgent, IPromptsService, PromptsStorage } from '../../../../common/promptSyntax/service/promptsService.js';
+import { ExtensionAgentSourceType, ICustomAgent, ICustomAgentQueryOptions, IPromptsService, PromptsStorage } from '../../../../common/promptSyntax/service/promptsService.js';
 import { PromptsService } from '../../../../common/promptSyntax/service/promptsServiceImpl.js';
 import { mockFiles } from '../testUtils/mockFilesystem.js';
 import { InMemoryStorageService, IStorageService } from '../../../../../../../platform/storage/common/storage.js';
@@ -1071,6 +1071,58 @@ suite('PromptsService', () => {
 			assert.strictEqual(actual[0].type, PromptsType.instructions);
 			registered.dispose();
 		});
+
+		test('Custom agent provider', async () => {
+			const agentUri = URI.parse('file://extensions/my-extension/myAgent.agent.md');
+			const extension = {
+				identifier: { value: 'test.my-extension' },
+				enabledApiProposals: ['chatParticipantPrivate']
+			} as unknown as IExtensionDescription;
+
+			// Mock the agent file content
+			await mockFiles(fileService, [
+				{
+					path: agentUri.path,
+					contents: [
+						'---',
+						'description: \'My custom agent from provider\'',
+						'tools: [ tool1, tool2 ]',
+						'---',
+						'I am a custom agent from a provider.',
+					]
+				}
+			]);
+
+			const provider = {
+				provideCustomAgents: async (_options: ICustomAgentQueryOptions, _token: CancellationToken) => {
+					return [
+						{
+							name: 'myAgent',
+							description: 'My custom agent from provider',
+							uri: agentUri
+						}
+					];
+				}
+			};
+
+			const registered = service.registerCustomAgentsProvider(extension, provider);
+
+			const actual = await service.getCustomAgents(CancellationToken.None);
+			assert.strictEqual(actual.length, 1);
+			assert.strictEqual(actual[0].name, 'myAgent');
+			assert.strictEqual(actual[0].description, 'My custom agent from provider');
+			assert.strictEqual(actual[0].uri.toString(), agentUri.toString());
+			assert.strictEqual(actual[0].source.storage, PromptsStorage.extension);
+			if (actual[0].source.storage === PromptsStorage.extension) {
+				assert.strictEqual(actual[0].source.type, ExtensionAgentSourceType.provider);
+			}
+
+			registered.dispose();
+
+			// After disposal, the agent should no longer be listed
+			const actualAfterDispose = await service.getCustomAgents(CancellationToken.None);
+			assert.strictEqual(actualAfterDispose.length, 0);
+		});
 	});
 
 	suite('findClaudeSkills', () => {

src/vscode-dts/vscode.proposed.chatParticipantPrivate.d.ts

@@ -314,4 +314,73 @@ declare module 'vscode' {
 	}
 
 	// #endregion
+
+	// #region CustomAgentsProvider
+
+	/**
+	 * Represents a custom agent resource file (e.g., .agent.md or .prompt.md) available for a repository.
+	 */
+	export interface CustomAgentResource {
+		/**
+		 * The unique identifier/name of the custom agent resource.
+		 */
+		readonly name: string;
+
+		/**
+		 * A description of what the custom agent resource does.
+		 */
+		readonly description: string;
+
+		/**
+		 * The URI to the agent or prompt resource file.
+		 */
+		readonly uri: Uri;
+	}
+
+	/**
+	 * Target environment for custom agents.
+	 */
+	export enum CustomAgentTarget {
+		GitHubCopilot = 'github-copilot',
+		VSCode = 'vscode',
+	}
+
+	/**
+	 * Options for querying custom agents.
+	 */
+	export interface CustomAgentQueryOptions {
+		/**
+		 * Filter agents by target environment.
+		 */
+		readonly target?: CustomAgentTarget;
+	}
+
+	/**
+	 * A provider that supplies custom agent resources (from .agent.md and .prompt.md files) for repositories.
+	 */
+	export interface CustomAgentsProvider {
+		/**
+		 * An optional event to signal that custom agents have changed.
+		 */
+		onDidChangeCustomAgents?: Event<void>;
+
+		/**
+		 * Provide the list of custom agent resources available for a given repository.
+		 * @param options Optional query parameters.
+		 * @param token A cancellation token.
+		 * @returns An array of custom agent resources or a promise that resolves to such.
+		 */
+		provideCustomAgents(options: CustomAgentQueryOptions, token: CancellationToken): ProviderResult<CustomAgentResource[]>;
+	}
+
+	export namespace chat {
+		/**
+		 * Register a provider for custom agents.
+		 * @param provider The custom agents provider.
+		 * @returns A disposable that unregisters the provider when disposed.
+		 */
+		export function registerCustomAgentsProvider(provider: CustomAgentsProvider): Disposable;
+	}
+
+	// #endregion
 }