Windows test fixes (bd-web8):
- Add sanitizeMetadataKey() to replace colons with underscores
- Windows absolute paths (e.g., C:\...) contain colons that conflict with
metadata key separator ':'
- Update tests to use sanitized keys when checking metadata
- Tests now pass on Windows by auto-sanitizing path-based keys
Nix flake fixes (bd-8y1a):
- Update vendorHash in default.nix to match current Go module dependencies
- Hash mismatch was causing Nix build failures in CI
Test improvements:
- Rename TestUpdateExportMetadataInvalidKeySuffix to reflect new behavior
- Test now verifies sanitization instead of rejection
- All tests pass locally
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>
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