feat(core): transition sub-agents to XML format and improve definitions (#18555)

packages/core/src/prompts/utils.ts

@@ -9,6 +9,8 @@ import process from 'node:process';
 import { homedir } from '../utils/paths.js';
 import { debugLogger } from '../utils/debugLogger.js';
 import type { Config } from '../config/config.js';
+import * as snippets from './snippets.js';
+import * as legacySnippets from './snippets.legacy.js';
 
 export type ResolvedPath = {
   isSwitch: boolean;
@@ -63,15 +65,25 @@ export function applySubstitutions(
   prompt: string,
   config: Config,
   skillsPrompt: string,
+  isGemini3: boolean = false,
 ): string {
   let result = prompt;
 
   result = result.replace(/\${AgentSkills}/g, skillsPrompt);
-  result = result.replace(
-    /\${SubAgents}/g,
-    config.getAgentRegistry().getDirectoryContext(),
+
+  const activeSnippets = isGemini3 ? snippets : legacySnippets;
+  const subAgentsContent = activeSnippets.renderSubAgents(
+    config
+      .getAgentRegistry()
+      .getAllDefinitions()
+      .map((d) => ({
+        name: d.displayName || d.name,
+        description: d.description,
+      })),
   );
 
+  result = result.replace(/\${SubAgents}/g, subAgentsContent);
+
   const toolRegistry = config.getToolRegistry();
   const allToolNames = toolRegistry.getAllToolNames();
   const availableToolsList =