Prototype optional Clang-enriched C++ resolution

[devkyato]

Goal

Evaluate an optional Clang-backed enrichment layer for projects that already have suitable compile information, while keeping Relay's standard-library structural parser as the complete default experience.

Constraints

• no compiler, Arduino CLI, PlatformIO, Docker, Java, or Node requirement for core analysis
• no automatic external-command execution
• no analysed-code execution
• failure or absence of Clang must fall back cleanly to the core parser

Acceptance criteria

• document the integration boundary and threat model
• prototype opt-in function/call resolution using existing compile metadata only
• compare findings against deterministic macro, overload, template, and cross-file fixtures
• clearly identify which facts came from Clang versus Relay heuristics
• benchmark startup, memory, and fallback behaviour
• make no change to default offline operation