fix(B-0557): truly cwd-independent — import.meta.dir fallback

[AceHack]

Summary

• Closes the scope gap that Copilot flagged on PR #3819: slice 3's cwd-independence acceptance bullet (`cd /tmp && bun /path/to/...`) was only partially shipped — git rev-parse --show-toplevel from /tmp fails (no git repo), and my fallback to process.cwd() returned /tmp which has no backlog.
• Fix: when git rev-parse fails, fall back to path.resolve(import.meta.dir, "../.."). The tool lives at <repo>/tools/hygiene/X.ts so two levels up reaches the repo root regardless of cwd.

Verification

Smoke from /tmp (the original failing case):

$ cd /tmp && bun /path/to/tools/hygiene/audit-backlog-status-drift.ts --json | head -5
# Now produces the same 33+ candidate output as running from the repo root
# (was previously empty `[]`).

Test plan

• bun test → 20 pass / 0 fail / 40 expect calls (no regression)
• Smoke from /tmp now produces 33+ candidates (was empty)
• git rev-parse still preferred when available (subdir-of-repo case)
• Closes the scope-honesty gap on PR chore(b-0557): close row — all 4 quality slices shipped (infrastructure-eats-itself) #3819

Unblocks PR #3819

Once this PR lands, PR #3819 (B-0557 close-row) can resolve its outstanding thread — slice 3's acceptance is now fully shipped, not partial.

🤖 Generated with Claude Code

[Copilot]

Pull request overview

This PR completes B-0557 slice 3’s “cwd-independence” guarantee for tools/hygiene/audit-backlog-status-drift.ts by making repo-root detection work even when invoked from outside any git worktree (e.g., /tmp), ensuring backlog-relative reads and existsSync checks remain correct.

Changes:

• Update detectRepoRoot() to prefer git rev-parse --show-toplevel, but when that fails, fall back to deriving the repo root from the script’s own location via import.meta.dir.
• Add a hygiene-history tick log entry documenting the related audit/close activity.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
tools/hygiene/audit-backlog-status-drift.ts	Make repo-root detection robust when executed outside a git repo by falling back to resolve(import.meta.dir, "../..").
docs/hygiene-history/ticks/2026/05/16/0758Z.md	Add tick log entry for the session/audit context.