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ADR-005 — First-party CPU feature detection

  • Identifier: ADR-005
  • Title: First-party CPU feature detection
  • Status: Accepted
  • Source: extracted verbatim from the Engineering PRD, docs/prd/07-runtime-dispatch.md (REQ-DOC-004). From M0 onward this file is the canonical, living ADR record; status changes happen here and in the index, with the PRD text remaining the historical record.

ADR-005 — First-party CPU feature detection. Status: Accepted. Context: zero-dependency pledge (Charter T4); need OS-state-correct AVX detection. Alternatives: (1) libcpuid/other library — rejected: dependency; (2) compiler builtins __builtin_cpu_supports — rejected: no VBMI2/OS-state granularity guarantees across toolchains, MSVC absent; (3) first-party CPUID/XGETBV + getauxval + sysctl (selected; ~150 lines, SDM/ARM-ARM-cited). Consequences: platform table maintained in docs/internals/cpu-detection.md. Reconsideration: new OS/arch targets. Related: REQ-DISP-004, REQ-INT-001.