Problem

No built-in way to verify repository consistency. There is no check that all objects referenced by commits/trees actually exist, that ref targets are valid, or that object content matches its SHA.

Impact

• Silent corruption goes undetected
• No way to verify backup integrity
• Cannot detect partial upload failures on S3

Acceptance Criteria

• Verify all object SHAs match their content
• Verify object graph completeness (all referenced objects exist)
• Verify all refs point to existing objects
• Verify pack checksums
• Report: list of errors found with details
• Configurable: full scan vs. quick (refs-only) mode
• Works across all storage backends
• Tests covering: corrupted object, missing object, dangling ref, valid repo