[verified] Align broker fixtures with descriptor-relative socket paths

harness/tests/README.md

@@ -21,6 +21,14 @@ trees under `/opt/data/gitea-agent/harness/tests/{common,spec,impl,review}`.
 This document is owned by the canonical harness tests and must be updated in
 place when their supported discovery contract or command paths change.
 
+Broker fixture contract: in-process broker fixtures bind and connect through
+`/proc/self/fd/{parent_fd}/{socket_name}`, matching the production broker. Long
+UTF-8 roots and socket paths are supported; the fixture must not shorten them or
+reject them merely because the conventional Unix-domain path encoding exceeds
+107 bytes. Fixture setup failures clean up only resources they own, preserve
+foreign/replaced paths, close every client and directory descriptor, and retain
+unauthenticated-token rejection behavior.
+
 It validates all `test*.py` files recursively under exactly these required
 roles: `common`, `spec`, `impl`, and `review`. `harness/tests`, every role, and
 every nested test package must have an `__init__.py`; every role and every