0014: Native sorting in one executable

Status: accepted. Supersedes ADR 0006: Supervise the system sort for the remaining sort routes.

Use built-in stable sorting for every calculation and sorted duplicate removal on Linux and macOS. The native sorter already preserves complete records, contribution order, seeded randomness and checked Spill storage. Keeping a second sort implementation would retain an executable, a process protocol and platform-specific failure paths for the same work.

Fastmash builds and installs as one executable. Keep the native temporary-file, entropy, signal, memory and thread helpers still needed by sorting and other commands. Remove the system-sort route, supervisor and their startup requirements. The Numerical profile is unchanged. Input and storage failures use Fastmash’s own diagnostics and existing exit statuses.

Upgrades remove a stale supervisor only when it belongs to the installation being replaced. Published releases, checksums and historical qualification evidence remain unchanged. Release publication is separate from this development change.