fix(cli): ensure on_session_end hook fires on interrupted exits (#4159)

- Add SIGTERM/SIGHUP signal handlers for graceful shutdown
- Add BrokenPipeError to exit exception handling (SSH disconnects)
- Fire on_session_end plugin hook in finally block, guarded by
  _agent_running to avoid double-firing on normal exits (the hook
  already fires per-turn from run_conversation)

Co-authored-by: kelsia14 <kelsia14@users.noreply.github.com>

cli.py

@@ -7447,6 +7447,20 @@ class HermesCLI:
         # Register atexit cleanup so resources are freed even on unexpected exit
         atexit.register(_run_cleanup)
         
+        # Register signal handlers for graceful shutdown on SSH disconnect / SIGTERM
+        def _signal_handler(signum, frame):
+            """Handle SIGHUP/SIGTERM by triggering graceful cleanup."""
+            logger.debug("Received signal %s, triggering graceful shutdown", signum)
+            raise KeyboardInterrupt()
+        
+        try:
+            import signal as _signal
+            _signal.signal(_signal.SIGTERM, _signal_handler)
+            if hasattr(_signal, 'SIGHUP'):
+                _signal.signal(_signal.SIGHUP, _signal_handler)
+        except Exception:
+            pass  # Signal handlers may fail in restricted environments
+        
         # Install a custom asyncio exception handler that suppresses the
         # "Event loop is closed" RuntimeError from httpx transport cleanup.
         # This is defense-in-depth — the primary fix is neuter_async_httpx_del
@@ -7470,7 +7484,7 @@ class HermesCLI:
                 except Exception:
                     pass
                 app.run()
-        except (EOFError, KeyboardInterrupt):
+        except (EOFError, KeyboardInterrupt, BrokenPipeError):
             pass
         finally:
             self._should_exit = True
@@ -7509,6 +7523,23 @@ class HermesCLI:
                     self._session_db.end_session(self.agent.session_id, "cli_close")
                 except (Exception, KeyboardInterrupt) as e:
                     logger.debug("Could not close session in DB: %s", e)
+            # Plugin hook: on_session_end — safety net for interrupted exits.
+            # run_conversation() already fires this per-turn on normal completion,
+            # so only fire here if the agent was mid-turn (_agent_running) when
+            # the exit occurred, meaning run_conversation's hook didn't fire.
+            if self.agent and getattr(self, '_agent_running', False):
+                try:
+                    from hermes_cli.plugins import invoke_hook as _invoke_hook
+                    _invoke_hook(
+                        "on_session_end",
+                        session_id=self.agent.session_id,
+                        completed=False,
+                        interrupted=True,
+                        model=getattr(self.agent, 'model', None),
+                        platform=getattr(self.agent, 'platform', None) or "cli",
+                    )
+                except Exception:
+                    pass
             _run_cleanup()
             self._print_exit_summary()