Further implementation notes:

Tracing support via metadata extensions (architectural decision)

Original plan: Add Source (string?) and CorrelationId (Guid?) as direct fields on the Error struct.

Implemented approach: Keep Error struct minimal and provide tracing support through metadata extensions via the
IHasOptionalMetadata<T> interface.

Rationale for deviation:

1. Smaller struct size: Keeping Error minimal improves cache locality and reduces memory footprint. Adding
   Source (8 bytes ref + 1 byte hasValue) and CorrelationId (16 bytes Guid + 1 byte hasValue) would add ~26 bytes
   per error.
2. Flexibility: Metadata-based approach allows arbitrary tracing properties without bloating the core Error type.
   Different applications may need different tracing identifiers (trace ID, span ID, request ID, etc.).
3. Opt-in overhead: Applications that don't use tracing don't pay for unused fields. Metadata allocation only occurs
   when explicitly needed.
4. Extensibility without breaking changes: New tracing properties can be added via extension methods without
   modifying the Error struct signature.

Implementation details:

• Introduced IHasOptionalMetadata<T> interface to unify metadata operations across Result<T>, Result, and
  potentially Error in the future
• Tracing extension methods in Light.Results.MetadataExtensions namespace provide:
  • WithSource(string source) - adds source identifier to metadata
  • WithCorrelationId(string correlationId) - adds correlation ID to metadata
  • WithTracing(string source, string correlationId) - adds both in one call
  • TryGetSource(out string? source) - retrieves source from metadata
  • TryGetCorrelationId(out string? correlationId) - retrieves correlation ID from metadata
• Uses string for correlation ID (not Guid) to support various formats (UUID, hex strings, custom formats)
• Metadata keys: "source" and "correlationId"

Trade-offs accepted:

• ❌ Requires metadata allocation for tracing (vs. inline fields)
• ❌ Lookup overhead via dictionary access (vs. direct field access)
• ✅ Significantly smaller Error struct
• ✅ Zero cost for non-tracing scenarios
• ✅ More flexible and extensible

Serialization implications:

• RFC 9457/gRPC serialization adapters should check both Error.Metadata and Result.Metadata for tracing properties
• Map metadata["source"] → extensions.source or instance
• Map metadata["correlationId"] → traceId or equivalent tracing header