feat(pi): add subagent tracer bullet

modules/agents/pi/extensions/subagents/runner.ts

@@ -0,0 +1,157 @@
+import { spawn, type ChildProcessWithoutNullStreams } from "node:child_process";
+import type { ChildHandle, ChildRunner, RunnerEvents, SpawnRequest } from "./types.ts";
+
+interface PendingResponse {
+  resolve(value: unknown): void;
+  reject(error: Error): void;
+  command: string;
+}
+
+interface RpcLine {
+  id?: string;
+  type?: string;
+  command?: string;
+  success?: boolean;
+  data?: unknown;
+  error?: string;
+  message?: string;
+}
+
+class RpcChildHandle implements ChildHandle {
+  private buffer = "";
+  private nextRequest = 0;
+  private settled = false;
+  private readonly pending = new Map<string, PendingResponse>();
+
+  constructor(
+    private readonly child: ChildProcessWithoutNullStreams,
+    private readonly events: RunnerEvents,
+  ) {
+    child.stdout.setEncoding("utf8");
+    child.stderr.setEncoding("utf8");
+    child.stdout.on("data", (chunk) => this.onStdout(chunk));
+    child.stderr.on("data", (chunk) => this.events.running(`stderr: ${String(chunk).trim().slice(0, 200)}`));
+    child.on("error", (error) => this.fail(error.message));
+    child.on("close", (code, signal) => {
+      for (const pending of this.pending.values()) {
+        pending.reject(new Error(`RPC process closed before ${pending.command} response`));
+      }
+      this.pending.clear();
+      if (!this.settled) this.fail(`RPC process closed with code ${code ?? "null"} signal ${signal ?? "null"}`);
+    });
+  }
+
+  async prompt(message: string): Promise<void> {
+    await this.send("prompt", { message });
+  }
+
+  async cancel(): Promise<void> {
+    try {
+      await this.send("abort", {});
+    } catch {}
+    this.child.stdin.end();
+    if (!this.child.killed) this.child.kill("SIGTERM");
+  }
+
+  private onStdout(chunk: string) {
+    this.buffer += chunk;
+    while (true) {
+      const newline = this.buffer.indexOf("\n");
+      if (newline === -1) return;
+      const line = this.buffer.slice(0, newline).replace(/\r$/, "");
+      this.buffer = this.buffer.slice(newline + 1);
+      if (line.trim() === "") continue;
+      this.onLine(line);
+    }
+  }
+
+  private onLine(line: string) {
+    let payload: RpcLine;
+    try {
+      payload = JSON.parse(line);
+    } catch {
+      this.events.running(`non-json rpc output: ${line.slice(0, 200)}`);
+      return;
+    }
+
+    if (payload.type === "response" && payload.id) {
+      const pending = this.pending.get(payload.id);
+      if (!pending) return;
+      this.pending.delete(payload.id);
+      if (payload.success) pending.resolve(payload.data);
+      else pending.reject(new Error(payload.error ?? payload.message ?? `${pending.command} failed`));
+      return;
+    }
+
+    if (payload.type === "agent_started") {
+      this.events.running("agent_started");
+      return;
+    }
+
+    if (payload.type === "agent_settled") {
+      this.finish().catch((error) => this.fail(error instanceof Error ? error.message : String(error)));
+      return;
+    }
+
+    if (payload.type) this.events.running(payload.type);
+  }
+
+  private async finish() {
+    if (this.settled) return;
+    this.settled = true;
+    this.events.settling();
+    const result = await this.send("get_last_assistant_text", {});
+    const text = typeof result === "string" ? result : result && typeof result === "object" && "text" in result ? String((result as { text: unknown }).text) : "";
+    this.events.completed(text, "agent_settled");
+    this.child.stdin.end();
+    if (!this.child.killed) this.child.kill("SIGTERM");
+  }
+
+  private fail(error: string) {
+    if (this.settled) return;
+    this.settled = true;
+    this.events.failed(error);
+  }
+
+  private send(command: string, body: Record<string, unknown>): Promise<unknown> {
+    const id = `subagent-${++this.nextRequest}`;
+    return new Promise((resolve, reject) => {
+      this.pending.set(id, { resolve, reject, command });
+      this.child.stdin.write(`${JSON.stringify({ id, type: command, ...body })}\n`, (error) => {
+        if (!error) return;
+        this.pending.delete(id);
+        reject(error);
+      });
+    });
+  }
+}
+
+export class SubprocessRpcRunner implements ChildRunner {
+  async start(id: string, request: SpawnRequest, cwd: string, events: RunnerEvents): Promise<ChildHandle> {
+    const args = [process.argv[1], "--mode", "rpc", "--no-extensions", "--name", `subagent ${id}`];
+    const child = spawn(process.execPath, args, {
+      cwd,
+      env: childEnvironment(),
+      stdio: ["pipe", "pipe", "pipe"],
+      detached: process.platform !== "win32",
+    });
+    const handle = new RpcChildHandle(child, events);
+    events.accepted();
+    void handle.prompt(independentPrompt(request)).catch((error) => events.failed(error instanceof Error ? error.message : String(error)));
+    return handle;
+  }
+}
+
+function childEnvironment(): NodeJS.ProcessEnv {
+  const env = { ...process.env };
+  delete env.PI_SESSION_ID;
+  delete env.PI_SESSION_FILE;
+  delete env.PI_PROVIDER;
+  delete env.PI_MODEL;
+  delete env.PI_REASONING_LEVEL;
+  return env;
+}
+
+function independentPrompt(request: SpawnRequest): string {
+  return `You are running as a delegated subagent in independent context.\nDo not assume access to the parent conversation transcript.\nReturn a concise final answer for the parent agent.\n\nTask:\n${request.prompt}`;
+}