fix(verification): keep passed uat results across verifier re-runs

A phase whose human UAT passed could loop forever between execute-phase
and verify-work. A gap-closure plan, or a later phase editing a covered
file, made the report stale; verify-work only recorded a passed UAT
against human_needed; the re-run verifier could not see the UAT file and
re-emitted human_needed; and execute-phase's human_needed branch then
rewrote *-UAT.md with every row back to [pending].

- verification.uat-evidence: recorded UAT rows plus the covered
  implementation files changed since the UAT. The verifier (Step 8b)
  treats a row that passed on unchanged code as verified and re-lists
  only affected rows, each with a retest_reason.
- verification.seed-uat: merges the report's human items into *-UAT.md.
  Existing rows are kept byte-for-byte; a pass is reset only with a
  recorded reason.
- verification.canonicalize-uat: the single human_needed -> passed flip,
  gated on the uat-only row predicate; refuses a stale report.
- verification.status reports stale_reason; init.progress lists every
  executed-but-stale phase in reverify_phases.
- verify-work and progress re-run the verifier themselves for a stale
  report instead of routing to execute-phase; execute-phase records a
  gap-closure checkpoint's UAT answers before dispatching the verifier.

Fail-closed properties are unchanged: a malformed fingerprint and a real
change to covered code still read stale.

Emitted-Drift-Ack-Growth: execute-phase.md — verify_phase_goal gains the gap-closure uat-record pointer and the merge-not-overwrite human_needed branch; the uat template it replaced moved into verification.seed-uat
Emitted-Drift-Ack-Growth: msd-verifier.md — new step 8b pointer to the lazily loaded verifier-uat-evidence reference plus the human_verified frontmatter key
Emitted-Drift-Ack-Growth: progress.md — route v.stale now re-verifies every stale executed phase in place instead of naming one command

.changeset/nimble-deer-purr.md

@@ -0,0 +1,5 @@
+---
+type: Fixed
+pr: 2
+---
+**A passed UAT is no longer discarded or re-requested after gap closure** — a phase whose human UAT passed could loop forever between `/msd-execute-phase` and `/msd-verify-work`: a gap-closure plan (or a later phase editing a covered file) made the report `stale`, the re-run verifier could not see the UAT file, and execute-phase then rewrote `*-UAT.md` with every row back to `[pending]`. The verifier now reads recorded UAT results as evidence (`verification.uat-evidence`) and re-requests only rows whose tested code changed; the UAT file is merged, never overwritten (`verification.seed-uat`); `verify-work` and `progress` re-run the verifier themselves for a stale report instead of routing to `execute-phase`; and `progress` offers every stale-but-executed phase as one re-verify action. `verification.status` now reports `stale_reason`. A real change to covered code still makes the report stale.