fix: add SIGTERM, SIGHUP handling and ignore SIGPIPE

- Add handler for SIGTERM to prevent "Terminated" message on Linux
- Add handler for SIGHUP for terminal closure handling
- Ignore SIGPIPE to prevent silent process termination
- Change os._exit(0) to sys.exit(0) for proper cleanup

Fixes issue #1365

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

nanobot/cli/commands.py

@@ -501,12 +501,17 @@ def agent(
         else:
             cli_channel, cli_chat_id = "cli", session_id
 
-        def _exit_on_sigint(signum, frame):
+        def _handle_signal(signum, frame):
+            sig_name = signal.Signals(signum).name
             _restore_terminal()
-            console.print("\nGoodbye!")
-            os._exit(0)
+            console.print(f"\nReceived {sig_name}, goodbye!")
+            sys.exit(0)
 
-        signal.signal(signal.SIGINT, _exit_on_sigint)
+        signal.signal(signal.SIGINT, _handle_signal)
+        signal.signal(signal.SIGTERM, _handle_signal)
+        signal.signal(signal.SIGHUP, _handle_signal)
+        # Ignore SIGPIPE to prevent silent process termination when writing to closed pipes
+        signal.signal(signal.SIGPIPE, signal.SIG_IGN)
 
         async def run_interactive():
             bus_task = asyncio.create_task(agent_loop.run())