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

packages/core/src/agents/registry.ts

@@ -481,37 +481,4 @@ export class AgentRegistry {
   getDiscoveredDefinition(name: string): AgentDefinition | undefined {
     return this.allDefinitions.get(name);
   }
-
-  /**
-   * Generates a markdown "Phone Book" of available agents and their schemas.
-   * This MUST be injected into the System Prompt of the parent agent.
-   */
-  getDirectoryContext(): string {
-    if (this.agents.size === 0) {
-      return 'No sub-agents are currently available.';
-    }
-
-    let context = '## Available Sub-Agents\n';
-    context += `Sub-agents are specialized expert agents that you can use to assist you in
-      the completion of all or part of a task.
-
-      Each sub-agent is available as a tool of the same name.
-
-      You MUST always delegate tasks to the sub-agent with the
-      relevant expertise, if one is available.
-
-      The following tools can be used to start sub-agents:\n\n`;
-
-    for (const [name] of this.agents) {
-      context += `- ${name}\n`;
-    }
-
-    context += `Remember that the closest relevant sub-agent should still be used even if its expertise is broader than the given task.
-
-    For example:
-    - A license-agent -> Should be used for a range of tasks, including reading, validating, and updating licenses and headers.
-    - A test-fixing-agent -> Should be used both for fixing tests as well as investigating test failures.`;
-
-    return context;
-  }
 }