CRITICAL FIX: Prevent check-in failure from seat upgrade lock contention

Flight C3GDAI's check-in FAILED because the seat upgrade function
held browser_session._lock for 10+ minutes while navigating
www.southwest.com. When the check-in thread (24h before departure)
tried to acquire the lock, it was blocked. When it finally got the
lock, the browser was on www.southwest.com (not mobile.southwest.com),
causing fetch() to fail with status 0 (same-origin policy violation).

Three fixes:

1. CRITICAL: Check-in proximity guard (worker.py)
   - attempt_seat_upgrades() now checks if ANY check-in is within
     2 hours. If so, seat upgrades are PAUSED entirely.
   - Check-in is always the jdholtz#1 priority. Seat upgrades can wait.
   - Activity log shows: "Seat upgrades PAUSED: check-in for X in Y minutes"

2. HIGH: Fresh browser session before check-in (checkin_handler.py)
   - 30 minutes before check-in, the handler now calls
     browser_session.start() (not just ensure_alive())
   - This creates a completely fresh browser on mobile.southwest.com
   - Guarantees the browser is on the correct domain with fresh WAF
     tokens, regardless of what seat upgrades did earlier

3. MEDIUM: Lock timeout in make_request (browser_session.py)
   - Changed from blocking `with self._lock:` to timed acquisition
     `self._lock.acquire(timeout=60)`
   - If the lock can't be acquired within 60 seconds, logs a warning
     and retries instead of blocking indefinitely
   - Prevents check-in from being stuck waiting for seat upgrade forever

https://claude.ai/code/session_01XeexS9xn1dz8wb9K11MkpV

Author: claude

worker/lib/browser_session.py

@@ -240,8 +240,18 @@ def make_request(
         while attempts < max_attempts:
             attempts += 1
             try:
-                with self._lock:
+                # Use timeout on lock to prevent indefinite blocking
+                # (seat upgrades can hold lock for minutes)
+                acquired = self._lock.acquire(timeout=60)
+                if not acquired:
+                    error_msg = "Browser session locked (another operation in progress)"
+                    logger.warning(error_msg)
+                    time.sleep(2)
+                    continue
+                try:
                     status, response_body = self.execute_fetch(method, url, merged_headers, body)
+                finally:
+                    self._lock.release()
 
                 if status == 200:
                     logger.debug("Browser fetch succeeded after %d attempts", attempts)

worker/lib/checkin_handler.py

@@ -138,13 +138,19 @@ def _wait_for_check_in(self, checkin_time: datetime) -> None:
             if self._stop_event.is_set():
                 return
 
-            # Ensure browser session is alive before check-in
+            # CRITICAL: Ensure browser is alive AND on mobile.southwest.com before check-in
+            # Seat upgrades may have navigated the browser to www.southwest.com,
+            # which causes fetch() to fail with status 0 (same-origin policy)
             if self.browser_session:
                 try:
-                    self.browser_session.ensure_alive()
+                    logger.info("Preparing browser for check-in: restarting fresh session")
+                    self.browser_session.start()  # Fresh browser on mobile.southwest.com
                     self.headers = self.browser_session.headers
+                    logger.info("Browser ready for check-in with %d headers", len(self.headers))
                 except DriverTimeoutError:
-                    logger.debug("Timeout while refreshing browser session before check-in")
+                    logger.warning("Timeout while preparing browser for check-in")
+                except Exception as e:
+                    logger.warning("Error preparing browser for check-in: %s", e)
 
             current_time = get_current_time()
 

worker/worker.py

@@ -616,11 +616,24 @@ def check_fares(conn: sqlite3.Connection) -> None:
 
 def attempt_seat_upgrades(conn: sqlite3.Connection, force_flight_id: str | None = None) -> None:
     """For A-List accounts, attempt seat upgrade from 48h to 2h before departure.
-    If force_flight_id is provided, only check that specific flight (bypasses cooldown)."""
+    If force_flight_id is provided, only check that specific flight (bypasses cooldown).
+    CRITICAL: Will NOT run if any check-in is imminent (within 2 hours)."""
     if not browser_session:
-        add_log(conn, "Seat upgrade check: browser session not available", "warning")
         return
 
+    # CRITICAL SAFETY CHECK: Do not interfere with upcoming check-ins
+    # Seat upgrades hold the browser lock for minutes, which blocks check-in threads
+    now_utc = datetime.utcnow()
+    for handler_id, handler in active_handlers.items():
+        try:
+            checkin_time = handler.departure_time - timedelta(days=1)
+            seconds_until_checkin = (checkin_time - now_utc.replace(tzinfo=handler.departure_time.tzinfo) if handler.departure_time.tzinfo else checkin_time - now_utc).total_seconds()
+            if 0 < seconds_until_checkin < 7200:  # Within 2 hours
+                add_log(conn, f"Seat upgrades PAUSED: check-in for {handler.confirmation_number} in {int(seconds_until_checkin / 60)} minutes. Check-in takes priority.", "info")
+                return
+        except Exception:
+            pass
+
     if force_flight_id:
         # Manual check for a specific flight - bypass normal query
         rows = conn.execute(