Implement atomic locking in API and cron steps for per-employee parallel sync

bitbylaw/steps/advoware_cal_sync/calendar_sync_cron_step.py

@@ -50,6 +50,19 @@ async def handler(context):
                 context.logger.info(f"DEBUG: Überspringe {kuerzel}, nur SB wird gesynct")
                 continue
 
+            employee_lock_key = f'calendar_sync_lock_{kuerzel}'
+
+            redis_client = redis.Redis(
+                host=Config.REDIS_HOST,
+                port=int(Config.REDIS_PORT),
+                db=int(Config.REDIS_DB_CALENDAR_SYNC),
+                socket_timeout=Config.REDIS_TIMEOUT_SECONDS
+            )
+
+            if redis_client.set(employee_lock_key, 'cron', ex=1800, nx=True) is None:
+                context.logger.info(f"Calendar Sync Cron: Sync bereits aktiv für {kuerzel}, überspringe")
+                continue
+
             # Emit event for this employee
             await context.emit({
                 "topic": "calendar_sync_employee",