Add a framework mechanism for prepared modules and validators to contribute checkpoint identity fingerprints

docs/internal/state.md

@@ -25,6 +25,9 @@ not `bypass`.
 `internal/framework/checkpoint` owns checkpoint identity, manifests, payload
 codecs, loader, and recorder. The CLI constructs a recorder whenever checkpoint
 recording is enabled and constructs a loader only for a `--resume` invocation.
+Identity incorporates explicit stable semantic fingerprints collected from
+prepared modules and validators in addition to configuration, input,
+references, runtime overrides, and LLM profiles.
 The serialized
 `workspace_schema_version` identifiers are frozen wire-compatibility fields;
 they do not describe a current public state surface.