Lane 6 of the test-improvement arc, pulled ahead of its own priority
list because every later lane's evidence is bite-shaped. A verifier
that cannot fail is worth no more than the claims it certifies.
The defect. The script ran only the SWAPPED tree, so "the tests failed
against the old file" was the only thing it ever checked. It could not
distinguish a load-bearing fix from a broken test: a typo, an unrelated
compile break, or a filter matching nothing all make the swapped run
fail, and each printed `bite: OK`.
The control now asserts two things, because passing alone is not
enough --- `cargo test` with a filter matching zero tests exits 0, and
a compile error in the old tree would then still read as OK:
* the named tests PASS against the working tree, and
* at least one test actually RAN,
exiting 3 as NO CONTROL otherwise. The swapped run additionally
distinguishes `OK (assertion)` from `OK (COMPILE)`, since an old file
that will not build against the current tree is much weaker evidence:
the tests may never have run at all.
Validated on all three paths rather than the happy one alone. A
zero-match filter reports NO CONTROL. A genuine bite --- PR #190's
`rd1`, which is known to fail against `main` --- reports `control OK
--- 1 test(s) pass` then `OK (assertion)`. A test deliberately broken
so it fails on BOTH trees reports NO CONTROL at exit 3; the previous
script printed `bite: OK` for exactly that case.
Handoff correction, verified rather than inherited. §5 claimed the
script "restores by `git checkout --`, which reverts the file to HEAD",
destroying uncommitted work, and cited a wiped review round during
#165. The mechanism description is false: the script copies the file to
a mktemp path before swapping and restores from that copy under an
`EXIT INT TERM` trap, touching no git state beyond a read-only
`git show`. The commit-before-gating rule is kept --- it stands on
gate-results-describe-the-pushed-tree --- but the false mechanism is
removed, because a reader who believes bite eats uncommitted work will
reach for `git stash` to protect themselves, which is the repo-global
trap the script exists to avoid.
No product code. No tests changed.
A trap-guarded one-file swap over read-only git show: run the named
tests against an older version of one file and exit 0 iff they FAIL
there (the fix bites); exit 1 flags a vacuous fix. The file is
restored on every exit path including interrupts; the ./ pathspec
prefix makes it work from any directory inside the repo. Never
touches git stash — the stash namespace is repo-global, shared
across worktrees and with humans (a #111-round mishap popped a
PR-#17-era user stash; hence the tool).
Dogfooded three ways against the merged #111 history: the round-1
fix commit bites (exit 0), the same tests against HEAD read as
vacuous (exit 1), and a docs/-relative invocation restores cleanly.
Handoff: section 1 snapshot (editops #111 merged, worktree folded),
section 5 lessons (repo-global stash; worktree-per-lane for
parallel work).
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018vF4gQVozBWi38y1SJiGfQ
Levi Neuwirth