Refactor subagent delegation to be one tool per agent (#17346)

packages/core/src/config/config.test.ts

@@ -155,8 +155,8 @@ vi.mock('../agents/registry.js', () => {
   return { AgentRegistry: AgentRegistryMock };
 });
 
-vi.mock('../agents/delegate-to-agent-tool.js', () => ({
-  DelegateToAgentTool: vi.fn(),
+vi.mock('../agents/subagent-tool.js', () => ({
+  SubagentTool: vi.fn(),
 }));
 
 vi.mock('../resources/resource-registry.js', () => ({
@@ -966,12 +966,15 @@ describe('Server Config (config.ts)', () => {
       AgentRegistryMock.prototype.getDefinition.mockReturnValue(
         mockAgentDefinition,
       );
+      AgentRegistryMock.prototype.getAllDefinitions.mockReturnValue([
+        mockAgentDefinition,
+      ]);
 
-      const DelegateToAgentToolMock = (
-        (await vi.importMock('../agents/delegate-to-agent-tool.js')) as {
-          DelegateToAgentTool: Mock;
+      const SubAgentToolMock = (
+        (await vi.importMock('../agents/subagent-tool.js')) as {
+          SubagentTool: Mock;
         }
-      ).DelegateToAgentTool;
+      ).SubagentTool;
 
       await config.initialize();
 
@@ -981,8 +984,8 @@ describe('Server Config (config.ts)', () => {
         }
       ).ToolRegistry.prototype.registerTool;
 
-      expect(DelegateToAgentToolMock).toHaveBeenCalledTimes(1);
-      expect(DelegateToAgentToolMock).toHaveBeenCalledWith(
+      expect(SubAgentToolMock).toHaveBeenCalledTimes(1);
+      expect(SubAgentToolMock).toHaveBeenCalledWith(
         expect.anything(), // AgentRegistry
         config,
         expect.anything(), // MessageBus
@@ -990,7 +993,7 @@ describe('Server Config (config.ts)', () => {
 
       const calls = registerToolMock.mock.calls;
       const registeredWrappers = calls.filter(
-        (call) => call[0] instanceof DelegateToAgentToolMock,
+        (call) => call[0] instanceof SubAgentToolMock,
       );
       expect(registeredWrappers).toHaveLength(1);
     });
@@ -1007,15 +1010,15 @@ describe('Server Config (config.ts)', () => {
       };
       const config = new Config(params);
 
-      const DelegateToAgentToolMock = (
-        (await vi.importMock('../agents/delegate-to-agent-tool.js')) as {
-          DelegateToAgentTool: Mock;
+      const SubAgentToolMock = (
+        (await vi.importMock('../agents/subagent-tool.js')) as {
+          SubagentTool: Mock;
         }
-      ).DelegateToAgentTool;
+      ).SubagentTool;
 
       await config.initialize();
 
-      expect(DelegateToAgentToolMock).not.toHaveBeenCalled();
+      expect(SubAgentToolMock).not.toHaveBeenCalled();
     });
 
     describe('with minified tool class names', () => {

packages/core/src/config/config.ts

@@ -101,8 +101,7 @@ import { getCodeAssistServer } from '../code_assist/codeAssist.js';
 import type { Experiments } from '../code_assist/experiments/experiments.js';
 import { AgentRegistry } from '../agents/registry.js';
 import { setGlobalProxy } from '../utils/fetch.js';
-import { DelegateToAgentTool } from '../agents/delegate-to-agent-tool.js';
-import { DELEGATE_TO_AGENT_TOOL_NAME } from '../tools/tool-names.js';
+import { SubagentTool } from '../agents/subagent-tool.js';
 import { getExperiments } from '../code_assist/experiments/experiments.js';
 import { ExperimentFlags } from '../code_assist/experiments/flagNames.js';
 import { debugLogger } from '../utils/debugLogger.js';
@@ -218,6 +217,7 @@ import {
 } from '../utils/extensionLoader.js';
 import { McpClientManager } from '../tools/mcp-client-manager.js';
 import type { EnvironmentSanitizationConfig } from '../services/environmentSanitization.js';
+import { getErrorMessage } from '../utils/errors.js';
 
 export type { FileFilteringOptions };
 export {
@@ -1967,8 +1967,7 @@ export class Config {
     }
 
     // Register Subagents as Tools
-    // Register DelegateToAgentTool if agents are enabled
-    this.registerDelegateToAgentTool(registry);
+    this.registerSubAgentTools(registry);
 
     await registry.discoverAllTools();
     registry.sortTools();
@@ -1976,27 +1975,36 @@ export class Config {
   }
 
   /**
-   * Registers the DelegateToAgentTool if agents or related features are enabled.
+   * Registers SubAgentTools for all available agents.
    */
-  private registerDelegateToAgentTool(registry: ToolRegistry): void {
+  private registerSubAgentTools(registry: ToolRegistry): void {
     const agentsOverrides = this.getAgentsSettings().overrides ?? {};
     if (
       this.isAgentsEnabled() ||
       agentsOverrides['codebase_investigator']?.enabled !== false ||
       agentsOverrides['cli_help']?.enabled !== false
     ) {
-      // Check if the delegate tool itself is allowed (if allowedTools is set)
       const allowedTools = this.getAllowedTools();
-      const isAllowed =
-        !allowedTools || allowedTools.includes(DELEGATE_TO_AGENT_TOOL_NAME);
+      const definitions = this.agentRegistry.getAllDefinitions();
 
-      if (isAllowed) {
-        const delegateTool = new DelegateToAgentTool(
-          this.agentRegistry,
-          this,
-          this.getMessageBus(),
-        );
-        registry.registerTool(delegateTool);
+      for (const definition of definitions) {
+        const isAllowed =
+          !allowedTools || allowedTools.includes(definition.name);
+
+        if (isAllowed) {
+          try {
+            const tool = new SubagentTool(
+              definition,
+              this,
+              this.getMessageBus(),
+            );
+            registry.registerTool(tool);
+          } catch (e: unknown) {
+            debugLogger.warn(
+              `Failed to register tool for agent ${definition.name}: ${getErrorMessage(e)}`,
+            );
+          }
+        }
       }
     }
   }
@@ -2092,7 +2100,7 @@ export class Config {
 
   private onAgentsRefreshed = async () => {
     if (this.toolRegistry) {
-      this.registerDelegateToAgentTool(this.toolRegistry);
+      this.registerSubAgentTools(this.toolRegistry);
     }
     // Propagate updates to the active chat session
     const client = this.getGeminiClient();