Grounds the native-Rust direction in what now exists: port inside-out, lowest risk
first, with tests/fixtures/track-format.json as the acceptance gate. Stage 1 (the
track-format crate as a third conformance adapter) is the concrete next PR -
host-testable in a container, no hardware. Toolchain goes in a container per the
develop-in-container rule, not the host.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
