What: attachOrReserveSpawn re-validates a ready backend whose /api/health
identity stayed unreadable (timeout, transport error, non-2xx, bad body)
for the whole wait budget with the token-only handshake instead of taking
the spawn gate. A backend that answers a different commit, or answers
without one, is still refused.
Why: d4e0c1347d5 made a transient read 'unknown' and retried it, but at the
end of the budget the loop fell through to the spawn reservation, so a
correct but persistently slow /api/health still produced a second backend
beside the first. Only a definitive non-matching commit is a mismatch.
Review: kshitijk4poor 5411222842 (host-attach identity read regression).
Red: start sha fails 'an identity unreadable for the whole budget keeps the
token attach' (reservation taken). Green: backend-discovery 21/21.
58d86507c3