Pure rustfmt reflow of the Task 2 (machine_uid dedup) and Task 4 (session
reaping) code; no logic change. The CI Build-Server-Linux job gates on
cargo fmt --check, which the two feature commits failed because local
validation ran check/clippy/test but not fmt --check. fmt --check, check,
and clippy -D warnings all clean now.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>