Fixes the three gremlins observed 2026-07-18 (bead
age-gate-scripts-worktree-gitdir-p62wo):
1. **Gate scripts broke under hook env from linked worktrees** (#919
regression): new scripts/lib/repo-root.sh (GIT_*-scrubbed resolution,
BASH_SOURCE anchor, worktree-correct) swept across 32 scripts. Proof:
this PR's own push ran the pre-push gates from a linked worktree and
passed.
2. **core.bare=true recurrence**: mechanism proven (leaked GIT_DIR +
no-arg git init --bare rewrites the SHARED config); writer traced with
high confidence to a live Gas City city process (concrete suspect:
gascity cmd_rig_test.go runGitInTest, unscrubbed env + no-arg init
--bare — fork-side fix filed separately). Defense: new
always.git-config-hygiene gate fails fast on core.bare/test identities
with the repair command inline (--self-test proves fail-closed).
3. **Test/test@test.com identity leak**: writer convicted — our own
pre-push chain leaked GIT_DIR into go test, whose helpers wrote the
shared config via git -C (mechanism proven). Cut at both ends:
validate-go-fast scrubs env for children; every test git-helper set-site
scrubs; check-test-isolation gains a WARN-ratchet rule (baseline 3 →
FAIL at 0).
Gates: shellcheck rc=0 across 36 scripts; go build/vet clean;
655+379+149 tests; hygiene self-test; both originally-failing validators
pass under the repro env.
Bo