feat(core): add adk.agentSessionSubagentEnabled flag (#26947)

packages/cli/src/config/settingsSchema.test.ts

@@ -571,6 +571,18 @@ describe('SettingsSchema', () => {
       expect(agentSessionNoninteractiveEnabled.description).toBe(
         'Enable non-interactive agent sessions.',
       );
+
+      const agentSessionSubagentEnabled =
+        adk.properties.agentSessionSubagentEnabled;
+      expect(agentSessionSubagentEnabled).toBeDefined();
+      expect(agentSessionSubagentEnabled.type).toBe('boolean');
+      expect(agentSessionSubagentEnabled.category).toBe('Experimental');
+      expect(agentSessionSubagentEnabled.default).toBe(false);
+      expect(agentSessionSubagentEnabled.requiresRestart).toBe(true);
+      expect(agentSessionSubagentEnabled.showInDialog).toBe(false);
+      expect(agentSessionSubagentEnabled.description).toBe(
+        'Route subagent invocations through the AgentSession protocol instead of legacy executors.',
+      );
     });
   });
 

packages/cli/src/config/settingsSchema.ts

@@ -2194,6 +2194,16 @@ const SETTINGS_SCHEMA = {
               'Enable the agent session implementation for the interactive CLI.',
             showInDialog: false,
           },
+          agentSessionSubagentEnabled: {
+            type: 'boolean',
+            label: 'Agent Session Subagent Enabled',
+            category: 'Experimental',
+            requiresRestart: true,
+            default: false,
+            description:
+              'Route subagent invocations through the AgentSession protocol instead of legacy executors.',
+            showInDialog: false,
+          },
         },
       },
       enableAgents: {

packages/core/src/config/config.ts

@@ -237,6 +237,7 @@ export interface GemmaModelRouterSettings {
 export interface ADKSettings {
   agentSessionNoninteractiveEnabled?: boolean;
   agentSessionInteractiveEnabled?: boolean;
+  agentSessionSubagentEnabled?: boolean;
 }
 
 export interface ExtensionSetting {
@@ -913,6 +914,7 @@ export class Config implements McpContext, AgentLoopContext {
   private readonly gemmaModelRouter: GemmaModelRouterSettings;
   private readonly agentSessionNoninteractiveEnabled: boolean;
   private readonly agentSessionInteractiveEnabled: boolean;
+  private readonly agentSessionSubagentEnabled: boolean;
 
   private readonly retryFetchErrors: boolean;
   private readonly maxAttempts: number;
@@ -1359,6 +1361,8 @@ export class Config implements McpContext, AgentLoopContext {
       params.adk?.agentSessionNoninteractiveEnabled ?? false;
     this.agentSessionInteractiveEnabled =
       params.adk?.agentSessionInteractiveEnabled ?? false;
+    this.agentSessionSubagentEnabled =
+      params.adk?.agentSessionSubagentEnabled ?? false;
     this.retryFetchErrors = params.retryFetchErrors ?? true;
     this.maxAttempts = Math.min(
       params.maxAttempts ?? DEFAULT_MAX_ATTEMPTS,
@@ -2573,6 +2577,10 @@ export class Config implements McpContext, AgentLoopContext {
     return this.contextManagement.enabled;
   }
 
+  isAgentSessionSubagentEnabled(): boolean {
+    return this.agentSessionSubagentEnabled;
+  }
+
   getMemoryBoundaryMarkers(): readonly string[] {
     return this.memoryBoundaryMarkers;
   }