Two findings from the live run on v1.73.0 (houseplan-e2e run
34393136097): the upgrade job carries the previous stable's tag in its
name, so "any job with HP <tag>" let a gate for v1.72.0 adopt the
v1.73.0 run — recognition now keys on `journeys`/`first-run`; and the
first poll after a dispatch sees only the matrix-planning job, which
marked the run as foreign forever — a run without any `· HP … ·` job is
undecided and polled again. Live: v1.73.0 → green with the run link,
v1.72.0 → no run of its own.
Issue: #514
User-Visible: no
Live run on v1.73.0 (houseplan-e2e run 34392391382): at `release:
published` the new tag is already the newest stable, so
`upgrade_from=stable` made the upgrade suite update v1.73.0 onto itself
and fail with `Expected: not "1.73.0"`. The gate now resolves the newest
non-prerelease, non-draft release other than the tag from `gh release
list` and passes it as `upgrade_from`; the first stable ever falls back
to `stable`. Spec §4/§6 record the change and the matrix-planning job in
houseplan-e2e (a job-level `if` cannot read `matrix.*`).
Mutant: release-upgrades-stable-onto-itself.
Issue: #514
User-Visible: no
