http_signature_invalid· code· HTTP 401· scope endpoint· applies to service_call, auth_decisionA per-delivery RFC 9421 HTTP Message Signature failed verification; the Content-Digest header profile, exact-content digest, or canonical-JSON wire check failed; or source_id disagreed with the Source-Service-ID header / signature transcript. Applies to Applet transaction push and to MIMI provider-to-provider writes (zh/extensions/mimi-interop.md §5). See zh/extensions/applet-integration.md §7.3.1.