Round-1 review fixes, canonical across box/rig/cast.
`gh issue edit --add-label` rejects the WHOLE call on one unknown label name,
applying nothing. Batching state and blockers into a single edit for
anti-flicker meant one missing `blocker:*` would take the `state:*`
convergence down with it — and since the taxonomy was only ever created by a
manual workflow_dispatch, the first sweep after the two-axis change would have
healed nothing on exactly the PRs it exists to fix, surfacing only as a log
line. The add side is now filtered against the repo's real label set, read
once per sweep. Removals need no filter (built from has_label, so they
provably exist); an unreadable label set filters nothing rather than
everything, because a failed read must not silently strip the board.
`checks_state` returns UNREADABLE when the `statusCheckRollup` key is absent —
what a failed `gh pr view` leaves behind — distinct from NONE for a
present-but-empty array. Collapsing the two let an API hiccup present as
"nothing is failing", i.e. as mergeable-by-a-human: the unknown-certified-as-
green shape this machine exists to stop, surviving where the #128 fix never
looked. The sweep now leaves that PR exactly as it is. Deliberately not a
blocker: blocking would flap the whole board on one bad call.
`blocker:unrequested` also fires on a STALE round, not just a MISSING one.
Both mean this head has no verdict from that reviewer and both owe an ask; the
stale round is the worse of the two, since it carries approvals on the page
that no longer describe the tree.
Fixtures 64 -> 68.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>