Server: Add file lock for blocklist loading

- Only one worker downloads blocklist
- Other workers wait and read from cache
- Prevents duplicate downloads on startup

server/main.py

@@ -53,29 +53,54 @@ async def lifespan(app: FastAPI):
     # Initialize logging
     init_logging()
     
-    # Load public blocklists (use cache if available)
+    # Load public blocklists (single worker loads, others wait for cache)
     USE_PUBLIC_BLOCKLIST = os.environ.get("PUBLIC_BLOCKLIST", "true").lower() == "true"
     all_blocked = set(MANUAL_BLOCKED_IPS)
     
     if USE_PUBLIC_BLOCKLIST:
         cached_ips = set()
+        
+        # Try to load from cache first
         if BLOCKLIST_CACHE_FILE.exists():
             try:
                 cached_ips = set(BLOCKLIST_CACHE_FILE.read_text().strip().splitlines())
-                logger.info(f"Loaded {len(cached_ips)} IPs from blocklist cache")
+                if cached_ips:
+                    logger.info(f"Loaded {len(cached_ips)} IPs from blocklist cache")
             except Exception as e:
                 logger.warning(f"Failed to load blocklist cache: {e}")
-                cached_ips = set()
         
+        # If no cache, download (only one worker will do this)
         if not cached_ips:
-            cached_ips = mw.load_public_blocklists()
-            if cached_ips:
+            DATA_DIR.mkdir(exist_ok=True)
+            lock_file = DATA_DIR / "blocklist.lock"
+            
+            try:
+                # Try to acquire lock (non-blocking)
+                import fcntl
+                lock_fd = open(lock_file, 'w')
                 try:
-                    DATA_DIR.mkdir(exist_ok=True)
-                    BLOCKLIST_CACHE_FILE.write_text("\n".join(cached_ips))
-                    logger.info(f"Saved {len(cached_ips)} IPs to blocklist cache")
-                except Exception as e:
-                    logger.warning(f"Failed to save blocklist cache: {e}")
+                    fcntl.flock(lock_fd, fcntl.LOCK_EX | fcntl.LOCK_NB)
+                    # We got the lock - download
+                    cached_ips = mw.load_public_blocklists()
+                    if cached_ips:
+                        BLOCKLIST_CACHE_FILE.write_text("\n".join(cached_ips))
+                        logger.info(f"Downloaded and saved {len(cached_ips)} IPs to blocklist cache")
+                except BlockingIOError:
+                    # Another process is downloading - wait for cache
+                    pass
+                finally:
+                    lock_fd.close()
+            except Exception as e:
+                logger.warning(f"Lock error: {e}")
+            
+            # Re-read cache after download
+            if BLOCKLIST_CACHE_FILE.exists() and not cached_ips:
+                try:
+                    cached_ips = set(BLOCKLIST_CACHE_FILE.read_text().strip().splitlines())
+                    if cached_ips:
+                        logger.info(f"Loaded {len(cached_ips)} IPs from blocklist cache (after wait)")
+                except Exception:
+                    pass
         
         all_blocked.update(cached_ips)