Auto: ablegacy-12 — auto-demote on comm failure

Closes #255

tests/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.IntegrationTests/Docker/docker-compose.yml

@@ -72,3 +72,30 @@ services:
       "--tag=F8[120]",
       "--tag=B3[10]"
     ]
+
+  # PR ablegacy-12 / #255 — faulty-PLC fixture for the auto-demote contract.
+  # FIXTURE-TIER FOLLOW-UP: implementing a refusing-proxy container that
+  # round-trips libplctag's CIP framing far enough to trigger comm failures
+  # (vs. just RST'ing the TCP handshake) is non-trivial — the integration
+  # test currently uses 127.0.0.1:1 (the bogus-port standard) which RST's
+  # immediately on most TCP stacks. That gets us deterministic comm-failure
+  # coverage without standing up a second container; if the localhost:1
+  # trick stops working on a future test runner (e.g. a sandbox that
+  # blocks port 1) re-enable this stub:
+  #
+  # slc500-faulty:
+  #   profiles: ["slc500-faulty"]
+  #   image: otopcua-ab-server:libplctag-release
+  #   build:
+  #     context: ../../ZB.MOM.WW.OtOpcUa.Driver.AbCip.IntegrationTests/Docker
+  #     dockerfile: Dockerfile
+  #   container_name: otopcua-ab-server-slc500-faulty
+  #   restart: "no"
+  #   ports:
+  #     - "44819:44819"
+  #   # Hostile entrypoint: bind the port but exit immediately so subsequent
+  #   # connection attempts get RST'd. Future iteration: a libplctag-aware
+  #   # proxy that accepts the CIP open and then drops the wire halfway
+  #   # through, exercising the read-timeout path rather than the
+  #   # connection-refused path.
+  #   entrypoint: ["sh", "-c", "exit 1"]