Summary

Establish clear separation between public and internal buffer APIs in preparation for C++20 module migration.

Parent Issue

Part of #309 (Consolidate buffering layer - C++20 Module preparation)

Current State

Public API (include/)

• thread_local_buffer.h - Used by central_collector
• time_series_buffer.h - Used by system_resource_collector

Internal API (src/utils/)

• ring_buffer.h - Core ring buffer implementation
• buffering_strategy.h - Buffering strategies
• buffer_manager.h - Buffer lifecycle management

Problem

• Unclear which buffers are public vs internal
• Internal implementations exposed through include paths
• C++20 modules need explicit export decisions

Proposed Solution

1. Document public vs internal distinction in header comments
2. Consider moving internal buffers to detail or internal namespace
3. Update include structure if needed for module preparation
4. Add @internal doxygen tags to internal APIs

Acceptance Criteria

• Clear documentation of public vs internal APIs
• Internal APIs marked appropriately
• No breaking changes to public API
• Ready for C++20 module partitioning

Files Affected

• All buffer-related headers
• Documentation files