diff --git a/bin/pty b/bin/pty
index ad5fcbb..08a9fbf 100755
--- a/bin/pty
+++ b/bin/pty
@@ -1,8 +1,9 @@
 #!/usr/bin/env node
 import { existsSync } from 'node:fs';
-import { spawnSync } from 'node:child_process';
+import { spawn } from 'node:child_process';
 import { fileURLToPath } from 'node:url';
 import { dirname, join } from 'node:path';
+import { constants as osConstants } from 'node:os';
 
 const __dirname = dirname(fileURLToPath(import.meta.url));
 const cli = join(__dirname, '..', 'dist', 'cli.js');
@@ -12,9 +13,38 @@ if (!existsSync(cli)) {
   process.exit(1);
 }
 
-const result = spawnSync(process.execPath, [cli, ...process.argv.slice(2)], {
+// `spawn` (not `spawnSync`) so the wrapper stays event-loop-live and can
+// react to signals it receives. Without this, signals delivered to the
+// wrapper (e.g. systemd's SIGTERM under KillMode=process) terminated the
+// wrapper without ever reaching the child supervisor, leaving an orphaned
+// supervisor that kept holding `supervisor.lock` and made every subsequent
+// service restart fail with "another supervisor is already running".
+const child = spawn(process.execPath, [cli, ...process.argv.slice(2)], {
   stdio: 'inherit',
   env: process.env,
 });
 
-process.exit(result.status ?? 1);
+const FORWARDED_SIGNALS = ['SIGTERM', 'SIGINT', 'SIGHUP', 'SIGQUIT', 'SIGUSR1', 'SIGUSR2'];
+for (const sig of FORWARDED_SIGNALS) {
+  process.on(sig, () => {
+    // Forward and let the child decide when to exit. The wrapper's own
+    // exit is driven by the child's 'exit' event so the child has time
+    // to flush before we propagate its status.
+    try { child.kill(sig); } catch {}
+  });
+}
+
+child.on('exit', (code, signal) => {
+  if (signal) {
+    // Mirror shell convention (128 + signum) so callers can distinguish
+    // signal death from a nonzero exit code.
+    const signum = osConstants.signals[signal] ?? 0;
+    process.exit(128 + signum);
+  }
+  process.exit(code ?? 1);
+});
+
+child.on('error', (err) => {
+  console.error(`pty: failed to spawn cli: ${err.message}`);
+  process.exit(1);
+});
diff --git a/tests/wrapper-signal-forwarding.test.ts b/tests/wrapper-signal-forwarding.test.ts
new file mode 100644
index 0000000..7806570
--- /dev/null
+++ b/tests/wrapper-signal-forwarding.test.ts
@@ -0,0 +1,97 @@
+// Verifies that bin/pty forwards SIGTERM/SIGINT to the inner cli.js child.
+// Without forwarding, systemd's KillMode=process leaves the inner supervisor
+// orphaned and still holding supervisor.lock — the new unit invocation then
+// fails with "another supervisor is already running".
+
+import { describe, it, expect, afterEach } from "vitest";
+import * as fs from "node:fs";
+import * as os from "node:os";
+import * as path from "node:path";
+import { fileURLToPath } from "node:url";
+import { spawn } from "node:child_process";
+
+const __dirname = path.dirname(fileURLToPath(import.meta.url));
+const wrapperPath = path.join(__dirname, "..", "bin", "pty");
+const nodeBin = process.execPath;
+
+const sessionDirs: string[] = [];
+const trackedPids: number[] = [];
+afterEach(() => {
+  // Belt-and-braces: if a test failed mid-way, kill any inner cli.js it left
+  // behind so the next run isn't poisoned by an orphan holding the lock.
+  for (const pid of trackedPids) {
+    try { process.kill(pid, "SIGKILL"); } catch {}
+  }
+  trackedPids.length = 0;
+  for (const d of sessionDirs) {
+    try { fs.rmSync(d, { recursive: true, force: true }); } catch {}
+  }
+  sessionDirs.length = 0;
+});
+
+function makeSessionDir(): string {
+  const dir = fs.mkdtempSync(path.join(os.tmpdir(), "pty-wrap-"));
+  sessionDirs.push(dir);
+  return dir;
+}
+
+/** Wait until predicate returns true or `timeoutMs` elapses. */
+async function waitFor(predicate: () => boolean, timeoutMs: number): Promise<boolean> {
+  const start = Date.now();
+  while (Date.now() - start < timeoutMs) {
+    if (predicate()) return true;
+    await new Promise((r) => setTimeout(r, 25));
+  }
+  return predicate();
+}
+
+function isAlive(pid: number): boolean {
+  try { process.kill(pid, 0); return true; } catch { return false; }
+}
+
+describe("bin/pty signal forwarding", () => {
+  it("propagates SIGTERM to the inner cli.js so the supervisor releases its lock", async () => {
+    const sessionDir = makeSessionDir();
+
+    // `supervisor start` is the canonical long-lived command and the one the
+    // dev3 regression hit. Its SIGTERM handler calls Supervisor.stop() which
+    // releases supervisor.lock — so a clean shutdown leaves no lock file.
+    const wrapper = spawn(nodeBin, [wrapperPath, "supervisor", "start"], {
+      env: { ...process.env, PTY_SESSION_DIR: sessionDir },
+      stdio: ["ignore", "pipe", "pipe"],
+    });
+
+    let stdout = "";
+    let stderr = "";
+    wrapper.stdout?.on("data", (d: Buffer) => { stdout += d.toString(); });
+    wrapper.stderr?.on("data", (d: Buffer) => { stderr += d.toString(); });
+
+    let exitCode: number | null = null;
+    let exitSignal: NodeJS.Signals | null = null;
+    wrapper.on("exit", (c, s) => { exitCode = c; exitSignal = s; });
+
+    // Wait for the supervisor to fully start (it writes supervisor.pid).
+    const pidPath = path.join(sessionDir, "supervisor", "supervisor.pid");
+    const lockPath = path.join(sessionDir, "supervisor.lock");
+    const ready = await waitFor(() => fs.existsSync(pidPath) && fs.existsSync(lockPath), 5000);
+    expect(ready, `supervisor never started; stdout=${stdout} stderr=${stderr}`).toBe(true);
+
+    const innerPid = parseInt(fs.readFileSync(pidPath, "utf-8").trim(), 10);
+    trackedPids.push(innerPid);
+    expect(innerPid).toBeGreaterThan(0);
+    expect(innerPid).not.toBe(wrapper.pid);
+    expect(isAlive(innerPid)).toBe(true);
+
+    // The actual test: SIGTERM the wrapper, expect the inner cli.js to also die.
+    wrapper.kill("SIGTERM");
+
+    const wrapperExited = await waitFor(() => exitCode !== null || exitSignal !== null, 5000);
+    expect(wrapperExited, "wrapper did not exit after SIGTERM").toBe(true);
+
+    const innerDied = await waitFor(() => !isAlive(innerPid), 5000);
+    expect(innerDied, `inner cli.js (pid ${innerPid}) survived wrapper SIGTERM — signal not forwarded`).toBe(true);
+
+    // Clean shutdown should release the lock; a SIGKILLed supervisor would leave it.
+    expect(fs.existsSync(lockPath), "supervisor.lock not released — child shutdown was not graceful").toBe(false);
+  }, 20000);
+});