feat: wire agent.delegate tool with sub-agent configs

- Export createAgentDelegateTool through builtin/index.ts → tools/index.ts
- Register agent.delegate in routing.ts with lazy orchestrator pattern
- Add agent.delegate + agents.list to messaging and coding policy profiles
- Add group:agents tool group to policy.ts
- Add research/code/comms agent config examples to default.yaml
- Add research/code/comms agent configs to user config.yaml
- Add 11 tests for agent-delegate tool (all pass)
- Typecheck clean, no regressions

src/backends/external.ts

@@ -0,0 +1,108 @@
+import { execFile } from 'child_process';
+
+export type ExternalBackendName = 'claude_code' | 'opencode' | 'codex' | 'gemini';
+
+export interface ExternalBackendRequest {
+  prompt: string;
+  history: Array<{ role: 'user' | 'assistant'; content: string }>;
+}
+
+export interface ExternalBackend {
+  name: ExternalBackendName;
+  process(input: ExternalBackendRequest): Promise<string>;
+}
+
+interface ExternalCliBackendOptions {
+  name: ExternalBackendName;
+  command: string;
+  args?: string[];
+  timeoutMs?: number;
+}
+
+const DEFAULT_TIMEOUT_MS = 120_000;
+
+function buildPrompt(request: ExternalBackendRequest): string {
+  const lines: string[] = [];
+  for (const item of request.history) {
+    if (!item.content.trim()) {
+      continue;
+    }
+    lines.push(`${item.role.toUpperCase()}: ${item.content}`);
+  }
+  lines.push(`USER: ${request.prompt}`);
+  return lines.join('\n\n');
+}
+
+function inferArgs(name: ExternalBackendName, prompt: string): string[] {
+  if (name === 'claude_code') {
+    return ['--print', prompt];
+  }
+  return ['-p', prompt];
+}
+
+export class ExternalCliBackend implements ExternalBackend {
+  readonly name: ExternalBackendName;
+  private readonly command: string;
+  private readonly args: string[];
+  private readonly timeoutMs: number;
+
+  constructor(options: ExternalCliBackendOptions) {
+    this.name = options.name;
+    this.command = options.command;
+    this.args = options.args ?? [];
+    this.timeoutMs = options.timeoutMs ?? DEFAULT_TIMEOUT_MS;
+  }
+
+  async process(input: ExternalBackendRequest): Promise<string> {
+    const prompt = buildPrompt(input);
+    const configuredArgs = this.args
+      .map((arg) => arg.includes('{prompt}') ? arg.replaceAll('{prompt}', prompt) : arg);
+    const hasPromptPlaceholder = this.args.some((arg) => arg.includes('{prompt}'));
+    const args = hasPromptPlaceholder
+      ? configuredArgs
+      : [...configuredArgs, ...inferArgs(this.name, prompt)];
+
+    const output = await execFileAsync(this.command, args, this.timeoutMs);
+    const trimmed = output.trim();
+    if (!trimmed) {
+      throw new Error(`External backend "${this.name}" returned no output`);
+    }
+    return trimmed;
+  }
+}
+
+export class ClaudeCodeBackend extends ExternalCliBackend {
+  constructor(path?: string, args?: string[], timeoutMs?: number) {
+    super({ name: 'claude_code', command: path ?? 'claude', args, timeoutMs });
+  }
+}
+
+export class OpenCodeBackend extends ExternalCliBackend {
+  constructor(path?: string, args?: string[], timeoutMs?: number) {
+    super({ name: 'opencode', command: path ?? 'opencode', args, timeoutMs });
+  }
+}
+
+export class CodexBackend extends ExternalCliBackend {
+  constructor(path?: string, args?: string[], timeoutMs?: number) {
+    super({ name: 'codex', command: path ?? 'codex', args, timeoutMs });
+  }
+}
+
+export class GeminiBackend extends ExternalCliBackend {
+  constructor(path?: string, args?: string[], timeoutMs?: number) {
+    super({ name: 'gemini', command: path ?? 'gemini', args, timeoutMs });
+  }
+}
+
+function execFileAsync(command: string, args: string[], timeoutMs: number): Promise<string> {
+  return new Promise((resolve, reject) => {
+    execFile(command, args, { timeout: timeoutMs, maxBuffer: 1024 * 1024 }, (error, stdout, stderr) => {
+      if (error) {
+        reject(new Error(`${error.message}${stderr ? `\n${stderr}` : ''}`));
+        return;
+      }
+      resolve(stdout || '');
+    });
+  });
+}