* test(#3995): diff base keys on the phase directory, not commit subjects
All three derivation sites (Tier 3, spawn_reviewer, fallow pre-pass)
must anchor on the phase directory's first commit; the milestone-blind
repro (an archived milestone's same-numbered phase commit capturing
the base) is the failing-first row. #3191/#3503 rows reworked to the
directory-anchor contract; T6 docs-parity forbids any remaining
phase-scope message-grep site.
* fix(#3995): derive the review diff base from the phase directory
A phase number is unique within a milestone, not a repository; the
message grep had no milestone bound and tail -1 deliberately selected
the oldest same-numbered subject, dragging archived milestones phases
into the scope (7 files to 3388 plus the >50 depth downgrade). All
three lockstep sites now anchor on the first commit that added anything
under the phase own directory — the same anchor class
git-base-branch phaseStartCommit uses. ShellCheck baseline gains the
escaped fragment shifted parse signature.
Emitted-Drift-Ack-Growth: code-review.md — phase-directory anchor replaces the message-grep derivation at both sites (#3995)
* chore(#3995): backfill changeset pr number
---------
Co-authored-by: sim <sim@local>
5c7243e54b