Allow reuse of socket (works without SELinux, probably no longer needed with proper workaround)

server.py

@@ -63,6 +63,12 @@ def _fd_to_socket(fd: int) -> socket.socket:
         # ``family``, ``type`` and ``proto`` attributes.
         sock = socket.socket(fileno=fd)
 
+        # Allow aiohttp to call listen() again without EPERM.
+        # On many Linux kernels the flag must be set *before* the first listen(),
+        # but systemd binds the socket without it.  Setting it now is sufficient
+        # for the second listen() performed by aiohttp.
+        sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEPORT, 1)
+        
         # aiohttp’s SockSite registers the socket with the event loop, which
         # requires a non‑blocking descriptor.
         sock.setblocking(False)