1 files changed, 85 insertions, 0 deletions
diff --git a/src/daemon/spawn.ts b/src/daemon/spawn.ts
new file mode 100644
index 0000000..e9f4d51
--- /dev/null
+++ b/src/daemon/spawn.ts
@@ -0,0 +1,85 @@
+/**
+ * Daemon lifecycle helpers — spawn detection and lazy launch.
+ *
+ * The daemon is a standalone long-lived process that owns the single WebSocket
+ * to Chrome. pi instances connect to it via a Unix domain socket. This module
+ * provides the plumbing to detect a running daemon and spawn one if needed.
+ *
+ * Reference:
+ *   - child_process.spawn detached: https://nodejs.org/docs/latest-v22.x/api/child_process.html#optionsdetached
+ */
+
+import { spawn, type ChildProcess } from "node:child_process";
+import { access } from "node:fs/promises";
+import { existsSync } from "node:fs";
+import { fileURLToPath } from "node:url";
+import { dirname, join } from "node:path";
+import { DAEMON_SOCKET_PATH } from "./protocol";
+
+const moduleDir = dirname(fileURLToPath(import.meta.url));
+
+/**
+ * Check whether the daemon is running by testing if its Unix socket exists.
+ * The socket file is created by the daemon on startup and removed on shutdown.
+ */
+export const isDaemonRunning = async (): Promise<boolean> => {
+  try {
+    await access(DAEMON_SOCKET_PATH);
+    return true;
+  } catch {
+    return false;
+  }
+};
+
+/**
+ * Spawn the daemon as a detached child process. The daemon will continue
+ * running after the parent pi process exits.
+ *
+ * The daemon entry point is resolved relative to this module. When running
+ * from source (tsx), the entry is src/daemon/index.ts. When running compiled,
+ * it's dist/daemon/index.js.
+ *
+ * Returns the child process handle (caller should call child.unref()).
+ */
+export const spawnDaemon = (): ChildProcess | null => {
+  // Resolve the daemon entry point and tsx binary.
+  const daemonScript = join(moduleDir, "index.ts");
+  const tsxBin = join(moduleDir, "..", "..", "node_modules", ".bin", "tsx");
+
+  // Use tsx to run the daemon TypeScript source directly.
+  // The spawed process inherits the parent's env so module resolution works.
+  // Fall back to `npx tsx` if the local binary isn't available.
+  const cmd = existsSync(tsxBin) ? tsxBin : "npx";
+  const args = existsSync(tsxBin) ? [daemonScript] : ["tsx", daemonScript];
+
+  const child = spawn(cmd, args, {
+    detached: true,
+    stdio: "ignore",
+    env: { ...process.env },
+  });
+
+  child.unref();
+  return child;
+};
+
+/**
+ * Ensure the daemon is running. If not, spawn it and wait (up to timeoutMs)
+ * for the socket file to appear.
+ *
+ * Returns true if the daemon is running (or was successfully spawned).
+ */
+export const ensureDaemon = async (timeoutMs = 10_000): Promise<boolean> => {
+  if (await isDaemonRunning()) return true;
+
+  const child = spawnDaemon();
+  if (!child) return false;
+
+  // Poll for the socket file to appear
+  const deadline = Date.now() + timeoutMs;
+  while (Date.now() < deadline) {
+    if (await isDaemonRunning()) return true;
+    await new Promise((r) => setTimeout(r, 200));
+  }
+
+  return false;
+};