docs(conformance): the GIVEN/WHEN/THEN header states the exception it now allows

conformance/tests/l0-static/prod-baremetal-not-dev-surface/check.sh

@@ -48,7 +48,10 @@
 #           sync.yaml, every patch it applies targets an ENVIRONMENT-SCOPED object
 #           (cluster-vars, a Flux Kustomization's sops decryption, or the Git source),
 #           prod's Git ref is the SAME ref dev tracks (no prod-only branch to develop on),
-#           and no prod-only manifest exists anywhere in the rendered configuration;
+#           and no prod-only manifest exists anywhere in the rendered configuration — a file
+#           whose NAME carries the environment token is excused ONLY when the tree proves it
+#           is an OVERLAY-SELECTED half that every environment applies (see the four
+#           conditions at "THE ONE STRUCTURAL EXCEPTION" below); anything else still fails;
 #       (6) prod artifacts exist only WITH a declaration of readiness: the spec roadmap
 #           carries the phase that opens prod build (checked when the spec repo is mounted),
 #           and the repository records that the operator opened it.