Preserve socket runtime directory

docs/wasm-runtime-architecture.md

@@ -150,6 +150,8 @@ owns `/run/uce/fastcgi.sock`; UCE validates and adopts the single named listener
 after exec. The listener therefore remains connectable and queues requests while
 the service and its post-fork workers restart. Direct launches without systemd
 activation retain the existing configured Unix/TCP listener behavior.
+The service preserves its runtime directory across service restarts because the
+socket unit, not the service unit, owns a listener path inside that directory.
 On termination the parent asks render workers to close their listeners, finish
 accepted connections within the bounded worker drain interval, and only then
 exits. This prevents an accepted FastCGI request from being reset at handoff;