M5a task 21. The work is Ornith's, from the stopped run; the design
model checked it against the task file and committed it after finding
that the gate's failure came from its own reference worktree's stale
test binaries in the shared target/ (fixed with cargo clean; 944 tests).
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>