diff --git a/tests/test_slash_worker_watchdog.py b/tests/test_slash_worker_watchdog.py
new file mode 100644
index 00000000000..198524c522d
--- /dev/null
+++ b/tests/test_slash_worker_watchdog.py
@@ -0,0 +1,21 @@
+import psutil
+
+from tui_gateway import slash_worker
+
+
+def test_is_orphaned_true_when_ppid_changes():
+    # Our parent went away and we were reparented to a subreaper/init.
+    assert slash_worker._is_orphaned(1234, 1.0, getppid=lambda: 999999) is True
+
+
+def test_is_orphaned_true_when_parent_create_time_mismatch():
+    # Same ppid but a different create_time means the PID was reused.
+    me = psutil.Process()
+    assert slash_worker._is_orphaned(me.pid, 0.0, getppid=lambda: me.pid) is True
+
+
+def test_is_orphaned_false_when_parent_alive_and_matches():
+    me = psutil.Process()
+    assert (
+        slash_worker._is_orphaned(me.pid, me.create_time(), getppid=lambda: me.pid) is False
+    )
diff --git a/tui_gateway/slash_worker.py b/tui_gateway/slash_worker.py
index 631b0c70450..49436d57449 100644
--- a/tui_gateway/slash_worker.py
+++ b/tui_gateway/slash_worker.py
@@ -9,11 +9,46 @@ import io
 import json
 import os
 import sys
+import threading
+import time
+
+import psutil
 
 import cli as cli_mod
 from cli import HermesCLI
 from rich.console import Console
 
+# Env-overridable so the integration test can drive sub-second timing.
+_WATCHDOG_POLL_S = float(os.environ.get("HERMES_SLASH_WATCHDOG_POLL_S", 2.0))
+_ORPHAN_GRACE_S = float(os.environ.get("HERMES_SLASH_WATCHDOG_GRACE_S", 5.0))
+_in_flight = threading.Event()  # set while a command is executing
+
+
+def _is_orphaned(original_ppid, parent_create_time, getppid=os.getppid) -> bool:
+    """True once our spawning gateway is gone. Compare to the ORIGINAL ppid
+    (never ==1: Linux reparents to a subreaper) and guard PID reuse via
+    create_time."""
+    if getppid() != original_ppid:
+        return True
+    try:
+        if not psutil.pid_exists(original_ppid):
+            return True
+        return psutil.Process(original_ppid).create_time() != parent_create_time
+    except psutil.Error:
+        return True
+
+
+def _start_parent_death_watchdog(original_ppid, parent_create_time) -> None:
+    def _loop():
+        while not _is_orphaned(original_ppid, parent_create_time):
+            time.sleep(_WATCHDOG_POLL_S)
+        deadline = time.monotonic() + _ORPHAN_GRACE_S
+        while _in_flight.is_set() and time.monotonic() < deadline:
+            time.sleep(0.05)  # let an in-flight command finish/flush
+        os._exit(0)
+
+    threading.Thread(target=_loop, daemon=True).start()
+
 
 def _run(cli: HermesCLI, command: str) -> str:
     cmd = (command or "").strip()
@@ -52,6 +87,15 @@ def main():
     os.environ["HERMES_SESSION_KEY"] = args.session_key
     os.environ["HERMES_INTERACTIVE"] = "1"
 
+    # Start before the (hundreds-of-ms) HermesCLI build — that window is itself
+    # an orphan risk if the gateway dies mid-spawn.
+    orig_ppid = os.getppid()
+    try:
+        parent_create_time = psutil.Process(orig_ppid).create_time()
+    except psutil.Error:
+        parent_create_time = 0.0
+    _start_parent_death_watchdog(orig_ppid, parent_create_time)
+
     with contextlib.redirect_stdout(io.StringIO()), contextlib.redirect_stderr(io.StringIO()):
         cli = HermesCLI(model=args.model or None, compact=True, resume=args.session_key, verbose=False)
 
@@ -60,6 +104,7 @@ def main():
         if not line:
             continue
 
+        _in_flight.set()
         rid = None
         try:
             req = json.loads(line)
@@ -70,6 +115,8 @@ def main():
         except Exception as e:
             sys.stdout.write(json.dumps({"id": rid, "ok": False, "error": str(e)}) + "\n")
             sys.stdout.flush()
+        finally:
+            _in_flight.clear()
 
 
 if __name__ == "__main__":