A single validation finding in the public report shape: the targeted entity is
carried as a nested entity struct and the source location is flattened into
individual line/column fields. The enrichment fields - documentation_url,
rule_description, phase, and context - are carried only when a report is
projected at the DETAILED detail level; the STANDARD detail level leaves them
None, so they are omitted from serialization.
The serializable validation result: report metadata, performance metrics, and
the flattened diagnostics. The per-diagnostic enrichment fields are present only
when the report is projected at the DETAILED detail level.