Share one discovery limiter across overlapping passes

A limiter created per invocation gave each discovery pass its own quota, so overlapping passes still scaled the number of simultaneous reads with the number of passes. Move the limiter to the service so all discovery reads share a single bound, and cover the overlapping-pass case in the test.

Author: abmahdy

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

@@ -68,6 +68,25 @@ const PROMPT_FILE_DISCOVERY_CONCURRENCY = 10;
 export class PromptsService extends Disposable implements IPromptsService {
 	public declare readonly _serviceBrand: undefined;
 
+	/**
+	 * Bounds how many prompt files discovery reads in parallel.
+	 *
+	 * Owned by the service rather than created per invocation on purpose: an
+	 * invalidation clears the cached discovery promise without cancelling the
+	 * computation it was tracking, so several passes can run at once. A limiter
+	 * per invocation would give each pass its own quota and the aggregate would
+	 * still grow with the number of passes, which is the exhaustion this bound
+	 * exists to prevent.
+	 */
+	private readonly _discoveryLimiter = this._register(new Limiter<unknown>(PROMPT_FILE_DISCOVERY_CONCURRENCY));
+
+	/**
+	 * Queues a discovery file read on the shared, service-wide limiter.
+	 */
+	private queueDiscoveryRead<T>(task: () => Promise<T>): Promise<T> {
+		return this._discoveryLimiter.queue(task) as Promise<T>;
+	}
+
 	/**
 	 * Prompt files locator utility.
 	 */
@@ -546,8 +565,7 @@ export class PromptsService extends Disposable implements IPromptsService {
 			...enabledSkills,
 		];
 
-		const slashCommandLimiter = new Limiter<ISlashCommandDiscoveryResult>(PROMPT_FILE_DISCOVERY_CONCURRENCY);
-		const parseResults = await Promise.all(slashCommandFiles.map(promptPath => slashCommandLimiter.queue(async () => {
+		const parseResults = await Promise.all(slashCommandFiles.map(promptPath => this.queueDiscoveryRead(async () => {
 			try {
 				const parsedPromptFile = await this.parseNew(promptPath.uri, token);
 				let rawName: string;
@@ -746,8 +764,7 @@ export class PromptsService extends Disposable implements IPromptsService {
 		const userHome = userHomeUri.scheme === Schemas.file ? userHomeUri.fsPath : userHomeUri.path;
 		const defaultFolder = this.workspaceService.getWorkspace().folders[0];
 
-		const agentLimiter = new Limiter<IAgentDiscoveryResult>(PROMPT_FILE_DISCOVERY_CONCURRENCY);
-		const files = await Promise.all(allAgentFiles.map(promptPath => agentLimiter.queue(async (): Promise<IAgentDiscoveryResult> => {
+		const files = await Promise.all(allAgentFiles.map(promptPath => this.queueDiscoveryRead(async (): Promise<IAgentDiscoveryResult> => {
 			const uri = promptPath.uri;
 			const isEnabled = !disabledAgents.has(uri);
 
@@ -1270,8 +1287,7 @@ export class PromptsService extends Disposable implements IPromptsService {
 			sourceUri?: URI;
 			hasDisabledClaudeHooks?: boolean;
 		};
-		const hookLimiter = new Limiter<HookFileResult>(PROMPT_FILE_DISCOVERY_CONCURRENCY);
-		const fileResults = await Promise.all(hookFiles.map(hookFile => hookLimiter.queue(async (): Promise<HookFileResult> => {
+		const fileResults = await Promise.all(hookFiles.map(hookFile => this.queueDiscoveryRead(async (): Promise<HookFileResult> => {
 			const name = basename(hookFile.uri);
 
 			// Plugins are handled separately down below because they do their own parsing+interpolation

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

@@ -972,6 +972,31 @@ suite('PromptsService', () => {
 				maxInFlight < agentCount,
 				`Must not read all ${agentCount} agent files at once, but read ${maxInFlight} concurrently.`,
 			);
+
+			// A discovery pass can be invalidated while it is still running, which
+			// starts a second pass alongside the first. Both passes must share the
+			// same quota, otherwise the number of open files grows with the number
+			// of passes.
+			const singlePassPeak = maxInFlight;
+			maxInFlight = 0;
+
+			const firstPass = service.getCustomAgents(CancellationToken.None);
+			const contributedAgent = URI.joinPath(rootFolderUri, '.github/agents/agent0.agent.md');
+			const registered = service.registerContributedFile(
+				PromptsType.agent,
+				contributedAgent,
+				{ identifier: new ExtensionIdentifier('test.extension'), name: 'test' } as IExtensionDescription,
+				undefined,
+				undefined,
+			);
+			const secondPass = service.getCustomAgents(CancellationToken.None);
+			await Promise.all([firstPass, secondPass]);
+			registered.dispose();
+
+			assert.ok(
+				maxInFlight <= singlePassPeak,
+				`Overlapping discovery passes must share one quota, but read ${maxInFlight} concurrently versus ${singlePassPeak} for a single pass.`,
+			);
 		});