63a5124 claimed "12 tests, 12 killed by at least one mutation", but the harness
that proved it lived in a session scratchpad. That left an unfalsifiable claim
about tests whose entire purpose is to not be vacuous -- and the facts it
encodes are exactly the ones a future edit to either hook would invalidate.
The mutations are per guard, not one whole-body gutting. Gutting a hook body
kills only the three positive tests, because a gutted hook emits neither a
launch nor any output, which is precisely what the nine negative tests expect.
Run that way the negative tests look vacuous when they are not; dropping each
guard in turn is what actually exercises them.
Two failure modes of the harness itself are handled. A mutation that leaves the
hook text unchanged now raises instead of quietly reporting "killed 0": a
behaviour-preserving edit to a hook, such as renaming a variable, would
otherwise turn a mutation into a no-op and weaken the proof without a word.
Verified by renaming count to n in a copy of the start hook -- the copy still
printed the correct banner, and the tool still refused it. And where the hooks
are not deployed at all the tool exits 0 rather than failing, since a CI runner
has no ~/.claude to mutate.
Wired into pre-commit scoped to the suite and the mutation definitions, the only
two files that can invalidate the proof. It costs ~40s, so it stays off
unrelated commits. It gates rather than warns: survivors mean exit 1.
One finding stands recorded: start-no-readable-guard kills nothing on its own.
The start hook's [[ ! -r "$STATE" ]] guard is redundant, since jq's stderr is
suppressed and an empty count already fails the arithmetic, so only the compound
mutation reaches those cases. The guard is left in place as defence in depth.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Krzysztof kuhy Rudnicki
7f706adb11