initFromManifest: a failed adopt of the socket listener should be non-fatal

open   by a73x

server.zig initFromManifest does 'try serve.adopt(d.listener_fd, sock_path)' for the unix socket, so an adopt that fails (path unlinked in the sub-millisecond window around the exec) aborts the upgrade and rolls back. The agent socket's adopt on the same path is non-fatal. With Server.watchSockPath in place, adopting with a lost path and letting the watch re-bind on its first tick is the consistent shape. Review finding 2026-09-05, judged not blocking for the socket-lifecycle branch.