fix: log WebUI shutdown diagnostics

server.py

@@ -8,6 +8,7 @@ import os
 import re
 import socket
 import sys
+import threading
 import time
 import traceback
 from http.server import BaseHTTPRequestHandler, ThreadingHTTPServer
@@ -403,6 +404,63 @@ def _raise_fd_soft_limit(target: int = 4096) -> dict:
     return {"status": "raised", "soft": desired, "hard": hard, "previous_soft": soft}
 
 
+_SHUTDOWN_AUDIT_LOGGED = False
+_SHUTDOWN_LOG_VALUE_RE = re.compile(r"[\x00-\x1f\x7f]+")
+
+
+def _shutdown_log_value(value, *, default: str = "unknown", max_len: int = 160) -> str:
+    """Return a bounded single-line value safe for shutdown diagnostics."""
+    if value is None:
+        return default
+    try:
+        text = str(value)
+    except Exception:
+        return default
+    text = _SHUTDOWN_LOG_VALUE_RE.sub("?", text).strip()
+    if not text:
+        return default
+    if len(text) > max_len:
+        text = f"{text[:max_len]}…"
+    return text
+
+
+def _log_shutdown_audit(reason: str = "serve_forever_exit") -> None:
+    """Log runtime context when the WebUI server is exiting."""
+    global _SHUTDOWN_AUDIT_LOGGED
+    if _SHUTDOWN_AUDIT_LOGGED:
+        return
+
+    active_sessions = []
+    try:
+        from api.models import LOCK, SESSIONS
+        with LOCK:
+            session_items = list(SESSIONS.items())
+        for sid, session in session_items:
+            stream_id = getattr(session, "active_stream_id", None)
+            if stream_id:
+                pending = bool(getattr(session, "pending_user_message", None))
+                active_sessions.append(
+                    "sid=%s stream=%s pending=%s"
+                    % (
+                        _shutdown_log_value(sid),
+                        _shutdown_log_value(stream_id),
+                        pending,
+                    )
+                )
+    except Exception:
+        logger.debug("Failed to collect active-session shutdown audit state", exc_info=True)
+
+    _SHUTDOWN_AUDIT_LOGGED = True
+    logger.info(
+        "[shutdown-audit] reason=%s pid=%s thread=%s(%s) active_sessions=[%s]",
+        _shutdown_log_value(reason),
+        os.getpid(),
+        _shutdown_log_value(threading.current_thread().name),
+        threading.current_thread().ident,
+        "; ".join(active_sessions) if active_sessions else "none",
+    )
+
+
 def main() -> None:
     from api.config import print_startup_config, verify_hermes_imports, _HERMES_FOUND
 
@@ -516,6 +574,7 @@ def main() -> None:
     try:
         httpd.serve_forever()
     finally:
+        _log_shutdown_audit()
         # Stop the gateway watcher on shutdown
         try:
             from api.gateway_watcher import stop_watcher