fix(tui-gateway): an ignored SIGINT no longer fences every later terminal command

A server started as `cmd &` from a non-interactive shell inherits SIGINT as
SIG_IGN. The exit-flush handler still ran _stop_turns_before_exit, which raises
the one-way foreground-spawn fence, then chained to the ignored disposition and
kept running: every later terminal command returned "[host is exiting: command
not started]" rc 130. An ignored signal ends nothing, so the handler now returns
before flushing or stopping turns.

tests/tui_gateway/test_serve_exit_flush.py

@@ -113,6 +113,27 @@ def test_sigterm_flushes_populated_session_into_state_db(
     assert any("survive the kill" in str(r.get("content", "")) for r in rows)
 
 
+def test_ignored_sigint_leaves_terminal_commands_runnable():
+    """SIGINT inherited as SIG_IGN (a server started as ``cmd &`` from a non-interactive shell) ends
+    nothing, so it must not raise the one-way exit fence: the process lives on and every later
+    terminal command would return 'host is exiting' rc 130."""
+    from tools.environments.local import LocalEnvironment
+
+    prev = {signal.SIGTERM: signal.getsignal(signal.SIGTERM),
+            signal.SIGINT: signal.signal(signal.SIGINT, signal.SIG_IGN)}
+    try:
+        assert server.install_exit_flush_signal_handlers() is True
+        os.kill(os.getpid(), signal.SIGINT)
+        time.sleep(0.05)
+    finally:
+        _restore_signal_state(prev)
+    env = LocalEnvironment(cwd=os.getcwd())
+    try:
+        assert env.execute("echo still-alive", timeout=30)["returncode"] == 0
+    finally:
+        env.cleanup()
+
+
 def test_exit_flush_is_bounded(registered_session):
     """A hung persist must never block exit longer than the budget."""
 

tui_gateway/session_reaper.py

@@ -151,17 +151,21 @@ _exit_flush_handlers_installed = False
 def _handle_exit_flush_signal(signum, frame) -> None:
     """Flush in-memory sessions, then hand off to the prior handler (uvicorn's graceful shutdown, a supervisor's
     handler, or the default disposition) — this only *prepends* a bounded flush."""
+    import signal as _signal
+    prev = _exit_flush_prev_handlers.get(signum)
+    if prev is _signal.SIG_IGN:
+        # An inherited ignore (`cmd &` from a non-interactive shell) ends nothing: stopping turns here
+        # would raise the one-way exit fence in a process that keeps running and refuses every command.
+        return
     with contextlib.suppress(Exception):
         _flush_sessions_before_exit()
     # The group signal that stopped us never reaches a command in its own session: reap it now,
     # before a supervisor's SIGKILL can cut the graceful shutdown (and its atexit) short.
     with contextlib.suppress(Exception):
         _stop_turns_before_exit()
-    import signal as _signal
-    prev = _exit_flush_prev_handlers.get(signum)
     if callable(prev):
         prev(signum, frame)
-    elif prev is not _signal.SIG_IGN:
+    else:
         # Default disposition: restore it and re-raise so the process dies with the correct signal (exit status
         # visible to supervisors).
         try: