Replace chat.subagents.maxDepth with chat.subagents.allowInvocationsF… (#304435)

Replace chat.subagents.maxDepth with chat.subagents.allowInvocationsFromSubagents

Author: aeschli

src/vs/workbench/contrib/chat/browser/chat.contribution.ts

@@ -1307,12 +1307,11 @@ configurationRegistry.registerConfiguration({
 				mode: 'auto'
 			}
 		},
-		[ChatConfiguration.SubagentsMaxDepth]: {
-			type: 'number',
-			description: nls.localize('chat.subagents.maxDepth', "Maximum nesting depth for subagents. Set to 0 to disable nested subagents. A subagent at this depth will not be able to launch further subagents."),
-			default: 0,
-			minimum: 0,
-			maximum: 20,
+		[ChatConfiguration.SubagentsAllowInvocationsFromSubagents]: {
+			type: 'boolean',
+			description: nls.localize('chat.subagents.allowInvocationsFromSubagents', "Allow subagents to invoke subagents."),
+			markdownDescription: nls.localize('chat.subagents.allowInvocationsFromSubagents.md', "Controls whether subagents can invoke other subagents. When enabled, nesting is limited to a maximum depth of 5."),
+			default: false,
 			experiment: {
 				mode: 'auto'
 			}

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

@@ -48,7 +48,7 @@ export enum ChatConfiguration {
 	ChatViewProgressBadgeEnabled = 'chat.viewProgressBadge.enabled',
 	ChatContextUsageEnabled = 'chat.contextUsage.enabled',
 	SubagentToolCustomAgents = 'chat.customAgentInSubagent.enabled',
-	SubagentsMaxDepth = 'chat.subagents.maxDepth',
+	SubagentsAllowInvocationsFromSubagents = 'chat.subagents.allowInvocationsFromSubagents',
 	ShowCodeBlockProgressAnimation = 'chat.agent.codeBlockProgress',
 	RestoreLastPanelSession = 'chat.restoreLastPanelSession',
 	ExitAfterDelegation = 'chat.exitAfterDelegation',

src/vs/workbench/contrib/chat/common/tools/builtinTools/runSubagentTool.ts

@@ -58,6 +58,8 @@ export interface IRunSubagentToolInputParams {
 	agentName?: string;
 }
 
+export const RUN_SUBAGENT_MAX_NESTING_DEPTH = 5;
+
 export class RunSubagentTool extends Disposable implements IToolImpl {
 
 	static readonly Id = 'runSubagent';
@@ -250,7 +252,8 @@ export class RunSubagentTool extends Disposable implements IToolImpl {
 			};
 
 			// Determine whether the subagent should be allowed to spawn its own subagents.
-			const maxDepth = this.configurationService.getValue<number>(ChatConfiguration.SubagentsMaxDepth) ?? 0;
+			const allowInvocationsFromSubagents = this.configurationService.getValue<boolean>(ChatConfiguration.SubagentsAllowInvocationsFromSubagents) ?? false;
+			const maxDepth = allowInvocationsFromSubagents ? RUN_SUBAGENT_MAX_NESTING_DEPTH : 0;
 			const sessionKey = invocation.context.sessionResource.toString();
 			const currentDepth = this._sessionDepth.get(sessionKey) ?? 0;
 			const depthAllowed = currentDepth + 1 <= maxDepth;
@@ -270,7 +273,7 @@ export class RunSubagentTool extends Disposable implements IToolImpl {
 			modeTools['copilot_askQuestions'] = false;
 
 			if (maxDepth > 0) {
-				this.logService.debug(`RunSubagentTool: Nested subagents enabling ${modeTools[RunSubagentTool.Id]}: session ${sessionKey}, currentDepth: ${currentDepth}, maxDepth: ${maxDepth}`);
+				this.logService.debug(`RunSubagentTool: Nested subagents enabling ${modeTools[RunSubagentTool.Id]}: session ${sessionKey}, currentDepth: ${currentDepth}, maxDepth: ${maxDepth}, allowInvocationsFromSubagents: ${allowInvocationsFromSubagents}`);
 			}
 
 			const variableSet = new ChatRequestVariableSet();

src/vs/workbench/contrib/chat/test/common/tools/builtinTools/runSubagentTool.test.ts

@@ -9,7 +9,7 @@ import { URI } from '../../../../../../../base/common/uri.js';
 import { ensureNoDisposablesAreLeakedInTestSuite } from '../../../../../../../base/test/common/utils.js';
 import { NullLogService } from '../../../../../../../platform/log/common/log.js';
 import { TestConfigurationService } from '../../../../../../../platform/configuration/test/common/testConfigurationService.js';
-import { RunSubagentTool } from '../../../../common/tools/builtinTools/runSubagentTool.js';
+import { RUN_SUBAGENT_MAX_NESTING_DEPTH, RunSubagentTool } from '../../../../common/tools/builtinTools/runSubagentTool.js';
 import { MockLanguageModelToolsService } from '../mockLanguageModelToolsService.js';
 import { IChatAgentHistoryEntry, IChatAgentRequest, IChatAgentResult, IChatAgentService, UserSelectedTools } from '../../../../common/participants/chatAgents.js';
 import { IChatProgress, IChatService } from '../../../../common/chatService/chatService.js';
@@ -502,12 +502,12 @@ suite('RunSubagentTool', () => {
 		 */
 		let callIdCounter = 0;
 		function createInvokableTool(opts: {
-			maxDepth: number;
+			allowInvocationsFromSubagents: boolean;
 			capturedRequests: IChatAgentRequest[];
 		}) {
 			const mockToolsService = testDisposables.add(new MockLanguageModelToolsService());
 			const configService = new TestConfigurationService({
-				[ChatConfiguration.SubagentsMaxDepth]: opts.maxDepth,
+				[ChatConfiguration.SubagentsAllowInvocationsFromSubagents]: opts.allowInvocationsFromSubagents,
 			});
 			const promptsService = new MockPromptsService();
 
@@ -565,9 +565,9 @@ suite('RunSubagentTool', () => {
 		const countTokens = async () => 0;
 		const noProgress: ToolProgress = { report() { } };
 
-		test('disables runSubagent tool when maxDepth is 0', async () => {
+		test('disables runSubagent tool when nesting is disabled', async () => {
 			const capturedRequests: IChatAgentRequest[] = [];
-			const { tool } = createInvokableTool({ maxDepth: 0, capturedRequests });
+			const { tool } = createInvokableTool({ allowInvocationsFromSubagents: false, capturedRequests });
 			const sessionUri = URI.parse('test://session/depth0');
 
 			await tool.invoke(createInvocation(sessionUri), countTokens, noProgress, CancellationToken.None);
@@ -576,9 +576,9 @@ suite('RunSubagentTool', () => {
 			assert.strictEqual(capturedRequests[0].userSelectedTools?.['runSubagent'], false);
 		});
 
-		test('enables runSubagent tool at depth 0 when maxDepth >= 1', async () => {
+		test('enables runSubagent tool at depth 0 when nesting is enabled', async () => {
 			const capturedRequests: IChatAgentRequest[] = [];
-			const { tool } = createInvokableTool({ maxDepth: 3, capturedRequests });
+			const { tool } = createInvokableTool({ allowInvocationsFromSubagents: true, capturedRequests });
 			const sessionUri = URI.parse('test://session/depth-enabled');
 
 			await tool.invoke(createInvocation(sessionUri), countTokens, noProgress, CancellationToken.None);
@@ -587,38 +587,40 @@ suite('RunSubagentTool', () => {
 			assert.strictEqual(capturedRequests[0].userSelectedTools?.['runSubagent'], true);
 		});
 
-		test('disables runSubagent tool when depth reaches maxDepth', async () => {
+		test('disables runSubagent tool when depth reaches hard limit', async () => {
 			const capturedRequests: IChatAgentRequest[] = [];
 			const sessionUri = URI.parse('test://session/depth-limit');
 
-			// maxDepth=1, so the first invoke (depth 0→1) should allow nesting,
-			// but the second invoke (depth 1→2) should not since 1+1 <= 1 is false.
-			const { tool, mockChatAgentService } = createInvokableTool({ maxDepth: 1, capturedRequests });
+			// When nesting is enabled, the tool enforces a hardcoded maximum depth of 5.
+			// Simulate nested invocation until we exceed the limit and ensure it disables nesting.
+			const { tool, mockChatAgentService } = createInvokableTool({ allowInvocationsFromSubagents: true, capturedRequests });
 
 			// Simulate nested invocation: the first invoke's invokeAgent callback
 			// triggers a second invoke on the same tool (same session).
 			capturedRequests.length = 0;
+			let nestedInvocations = 0;
 			mockChatAgentService.invokeAgent = async (_id: string, request: IChatAgentRequest) => {
 				capturedRequests.push(request);
-				// On the first call (depth 0), simulate a nested subagent call
-				if (capturedRequests.length === 1) {
+				// Keep nesting until we go beyond the hardcoded maxDepth
+				if (nestedInvocations++ < RUN_SUBAGENT_MAX_NESTING_DEPTH + 1) {
 					await tool.invoke(createInvocation(sessionUri), countTokens, noProgress, CancellationToken.None);
 				}
 				return {};
 			};
 
 			await tool.invoke(createInvocation(sessionUri), countTokens, noProgress, CancellationToken.None);
 
-			assert.strictEqual(capturedRequests.length, 2);
-			// First call at depth 0: should enable (0 + 1 <= 1)
-			assert.strictEqual(capturedRequests[0].userSelectedTools?.['runSubagent'], true);
-			// Second call at depth 1: should disable (1 + 1 <= 1 is false)
-			assert.strictEqual(capturedRequests[1].userSelectedTools?.['runSubagent'], false);
+			assert.ok(capturedRequests.length >= 2);
+			// At depth 0..(maxDepth-1), nesting is allowed. Once depth reaches maxDepth, the next call should disable nesting.
+			const enabledFlags = capturedRequests.map(r => r.userSelectedTools?.['runSubagent']);
+			assert.strictEqual(enabledFlags[0], true);
+			assert.strictEqual(enabledFlags[1], true);
+			assert.strictEqual(enabledFlags[RUN_SUBAGENT_MAX_NESTING_DEPTH], false);
 		});
 
 		test('depth is decremented after invoke completes', async () => {
 			const capturedRequests: IChatAgentRequest[] = [];
-			const { tool } = createInvokableTool({ maxDepth: 2, capturedRequests });
+			const { tool } = createInvokableTool({ allowInvocationsFromSubagents: true, capturedRequests });
 			const sessionUri = URI.parse('test://session/depth-decrement');
 
 			// First invoke