## Summary
Implements mandatory file hash validation for MCPB (MCP Bundle) packages
to ensure file integrity and security.
## Changes
- **Validator enforcement**: MCPB packages now require `file_sha256`
field at publish time
- **Test coverage**: Updated all MCPB test cases to include valid
SHA-256 hashes
- **Documentation**: Updated publisher guide and schema to reflect hash
requirement
- **Error handling**: Clear error message when hash is missing
## Security Impact
This ensures the complete security workflow for MCPB packages:
1. Authors generate and provide SHA-256 hashes when publishing
2. Registry validates hash is present (but doesn't verify content)
3. MCP clients validate hash matches downloaded file before installation
Fixes#351
8f5e17d0fe