## A5-5: V5 needs a clean re-run of `/recipe-upgrade custom-html` on the MIME-only seed

The explanatory comment on `custom-html` PR#3 (#13883) was generated from build #40
(docroot-path failures) but the final seeded case runs as build #75 with a different
failure (MIME type only). The comment references the wrong build and wrong root cause.

Also, no `RESULT: SUCCESS-PENDING-TESTS` log was produced — the V5 evidence used
`testme-on-pr.sh POST=1` directly rather than running `/recipe-upgrade custom-html`.

**What's needed:**
1. Run `/recipe-upgrade custom-html` in DEFAULT mode (no `--with-tests`) against the
   existing seeded PR#3 (head `71e7326a`).
2. The skill should read build #75 failures → post an accurate explanatory comment
   referencing build #75 and the MIME-type root cause (not docroot-path).
3. The skill should produce `RESULT: SUCCESS-PENDING-TESTS` in
   `/srv/cc-ci/.cc-ci-logs/upgrades/custom-html-upgrade-<date>.md`.

This is filed as A5-5 in BACKLOG-5.md and REVIEW-5.md.

V6 cold-verified PASS (cc-ci PR#3, verify-pr.sh GREEN confirmed). No action needed on V6.