Retires `state:needs-rebase` in favour of two independent axes: `state:*`
(whose ball, exactly one) and `blocker:*` (what is in the way, additive).
One rule joins them: `state:needs-human` requires zero blockers.
The single-label design projected independent facts — mergeability, check
status, review round — onto one totally-ordered value, so one always won
and the rest vanished. Every precedence bug this machine has had lived on
that ordering. Blockers are a set, so there is no precedence between them
to get wrong.
`state:bots-reviewing` tightens to mean strictly "a request is live"; a
ready PR nobody was asked to review is now `state:addressing` +
`blocker:unrequested`. The reconciler strips the retired
`state:needs-rebase` on sight via a RETIRED array.
Also wires test/labels-reconcile.sh into CI, where it had never run.
Fixtures 51 -> 64.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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