fix(review): harden unborn repository review handling

[barbatdev]

This focused child slice hardens the issue Gentleman-Programming#159 unborn-review implementation after CodeRabbit feedback. It does not replace the integration tracker.

Linked Issue

Refs Gentleman-Programming#159

PR Type

• Bug fix
• New feature
• Documentation only
• Code refactoring
• Maintenance/tooling
• Breaking change

Summary

• Treats only show-ref --verify --quiet status 1 as a valid unborn HEAD.
• Fails closed on timeout, corruption, and I/O failures.
• Uses the pre-2.42 worktree add --orphan compatibility fallback only for status 129.
• Adds focused tests for both boundaries.

Chain Context

main
  -> #305 integration tracker (draft, no merge yet)
      -> 📍 barbatdev/gentle-pi#1 review hardening

• Start: 429502d1
• End: 17d0edd9
• Dependency: fix(review): support unborn repository reviews Gentleman-Programming/gentle-shell#305
• Follow-up: none
• Out of scope: the original unborn-review implementation already lives in the tracker.

Review Map

1. lib/git-commit-transaction.ts
2. lib/review-candidate-view.ts
3. Focused tests and the runtime mirror

Review Budget

214 / 400 changed lines (207 additions + 7 deletions).

Why This Is Safe

• RDD receipt: sha256:3f1e760e85dd8bf7051b4920100699a7379cc7032860b2e2ad98bfe9555a798b
• pre-commit, pre-push, and pre-pr gates: allow
• Contributor HEAD, index, and refs remain untouched.
• The fallback uses deterministic metadata and creates no referenced phantom commit.

Verification

• git diff --check
• pnpm run check:transaction-runner
• node scripts/verify-package-files.mjs
• node --experimental-strip-types --test tests/git-commit-transaction.test.ts tests/review-candidate-view.test.ts (79/79 passed)

Rollback

Revert 17d0edd9 to remove only this hardening slice.

Reviewer Action

Review this child first. The tracker stays draft until the chain is complete.