Test coverage for 9 pure functions in internal/api/diagnostics.go:
- isFallbackMemorySource: 13 cases covering fallback and non-fallback sources
- copyStringSlice: 4 cases including nil handling and copy verification
- normalizeHostForComparison: 16 cases for URL normalization
- normalizeVersionLabel: 11 cases for version prefix handling
- contains: 8 cases for string slice membership
- containsFold: 11 cases for case-insensitive matching
- interfaceToStringSlice: 9 cases for type conversion
- preferredDockerHostName: 5 cases for name preference hierarchy
- formatTimeMaybe: 3 cases for time formatting
