A fall back to the old login during a rotation is now delivery.NodeHealth's Fallback (the node, the login fallen back from,
why, when), written with the node's health report, from which the watchman raises node-account-fallback; it is said no more
once the vault's key of the node moves on (blocker 7, ADR 0583 §6). mesh-host enrol's fall back to the controller's
enrolment subject says it is the path before the lease write, which the bus refuses once the lease is written. Tests: rows
in the existing rotation test; none added.
(issue 774)
Claude-Session: https://claude.ai/code/session_01NcbgfJ9Gum47zkFKWRaovL