fusion/plugins/fusion-plugin-acp-runtime/src/process-manager.ts

// port-4040-allowlist: doc comments below reference the "never kill port 4040" rule; no kill targets it.
// Subprocess lifecycle for the ACP runtime.
//
// Mirrors the hardening conventions in
// `plugins/fusion-plugin-droid-runtime/src/process-manager.ts`: a self-cleaning
// process registry, SIGKILL teardown scoped to agent subprocesses only (never
// the dashboard/port-4040 — KTD4), bounded stderr capture with secret redaction
// (Risk S8), and a high inactivity ceiling (the engine's StuckTaskDetector is
// the authoritative aborter — KTD4).
//
// The ACP agent is UNTRUSTED. The spawn env is built from an explicit allow-list
// (KTD6b), never inherited `process.env`, so secret-bearing vars are not handed
// to the agent.

import { spawn, type ChildProcess } from "node:child_process";
import { redactSecrets } from "@fusion/core";

function debugLog(message: string): void {
  if (process.env.PI_ACP_DEBUG !== "1") return;
  console.error(`[acp-runtime] ${message}`);
}

/** Registry of active agent subprocesses for teardown. Self-cleans on exit. */
const activeProcesses = new Set<ChildProcess>();

/**
 * Register a subprocess in the agent process registry.
 * Auto-removed from the registry when it exits.
 */
export function registerProcess(child: ChildProcess): void {
  activeProcesses.add(child);
  child.on("exit", () => activeProcesses.delete(child));
}

/** Remove a subprocess from the registry (idempotent). */
export function unregisterProcess(child: ChildProcess): void {
  activeProcesses.delete(child);
}

/** Number of registered (presumed-live) agent subprocesses — for diagnostics/tests. */
export function activeProcessCount(): number {
  return activeProcesses.size;
}

/**
 * Force-kill a subprocess via SIGKILL. No-op if already dead (killed or exited).
 * Cross-platform safe: Node treats SIGKILL as forceful termination on Windows.
 */
export function forceKill(child: ChildProcess): void {
  if (child.killed || child.exitCode !== null) return;
  try {
    child.kill("SIGKILL");
  } catch {
    // already gone
  }
}

/**
 * Force-kill every registered agent subprocess and clear the registry.
 *
 * Scoped to agent subprocesses tracked here only — never the dashboard / port
 * 4040 / any other process (KTD4 / kill-guard conventions). Safe to call
 * repeatedly; no-ops on already-dead processes.
 */
export function killAllProcesses(): void {
  for (const child of activeProcesses) {
    forceKill(child);
  }
  activeProcesses.clear();
}

/**
 * Build the subprocess environment from an explicit allow-list (KTD6b).
 *
 * Returns ONLY allow-listed vars copied from `process.env`. The full env is
 * never inherited — the agent is untrusted and must not receive secret-bearing
 * vars. Returns an empty env by default (empty allow-list).
 */
export function buildSpawnEnv(allowList: string[]): NodeJS.ProcessEnv {
  const env: NodeJS.ProcessEnv = {};
  for (const key of allowList) {
    const value = process.env[key];
    if (typeof value === "string") env[key] = value;
  }
  return env;
}

export interface SpawnAgentOptions {
  binaryPath: string;
  args: string[];
  cwd: string;
  env: NodeJS.ProcessEnv;
}

/**
 * Spawn the ACP agent subprocess with piped stdio.
 *
 * Registers the child on spawn and unregisters it on exit. The caller wraps
 * stdin/stdout into a web stream for `ndJsonStream`.
 */
export function spawnAgent(options: SpawnAgentOptions): ChildProcess {
  const child = spawn(options.binaryPath, options.args, {
    stdio: ["pipe", "pipe", "pipe"],
    cwd: options.cwd,
    env: options.env,
  });
  registerProcess(child);
  debugLog(`spawnAgent: pid=${child.pid} binary=${options.binaryPath}`);
  return child;
}

// --- stderr capture + secret redaction (Risk S8) --------------------------

/** Maximum stderr bytes retained; older output is dropped to bound memory. */
const STDERR_BUFFER_CEILING = 64 * 1024;

// Secret redaction (Risk S8) lives in @fusion/core so PTY/process owners share
// one implementation; re-exported here to preserve this module's public surface.
export { redactSecrets };

/**
 * Accumulate stderr into a bounded, secret-redacted buffer.
 * Returns a getter for the current (redacted) buffer contents.
 */
export function captureStderr(child: ChildProcess): () => string {
  // FIX 5: redacting each chunk in isolation leaks a secret that straddles a
  // chunk boundary (the token is split across two `data` events so neither half
  // matches a pattern). Accumulate the RAW bytes into a bounded buffer first,
  // then redact across the whole (bounded) buffer after each append so a
  // boundary-spanning secret is caught. The buffer stays bounded by the existing
  // ceiling; the returned getter always reports the redacted view.
  let raw = "";
  child.stderr?.on("data", (data: Buffer) => {
    raw += data.toString();
    if (raw.length > STDERR_BUFFER_CEILING) {
      raw = raw.slice(raw.length - STDERR_BUFFER_CEILING);
    }
  });
  return () => redactSecrets(raw);
}