Bind audio cache reuse to remote identity

docs/policy/architecture.md

@@ -157,6 +157,10 @@ Canonical helpers own workspace, spool, cache, session, run, input, transcript,
 artifact, log, report, configuration, and publish-current paths. Callers must
 not reconstruct canonical paths through scattered string concatenation.
 
+Reusable audio cache entries require a typed record that binds a confined,
+no-follow regular file and its digest to the selected remote object identity.
+Size alone and unqualified multipart ETags are not content-integrity evidence.
+
 Artifact resolution is deterministic and manifest-aware. Producers materialize
 canonical outputs before reporting success, and consumers resolve declared
 artifact identities rather than infer files from unrelated directory contents.