Cross-host federation: one operation centre controlling many hosts, instead of one bridged per host with leads and members local to it.
The admission rule is the mirror of 1.1's. If the problem disappears when there is exactly one host, it belongs here. If it would still be broken on a single host, it belongs in 1.1 — being federation-adjacent is not enough.
Nothing here should block the 1.1 tag. 1.1 makes the single-host story honest; this line extends it.
Detect a member that is failing rather than working, and stop the fleet spending on it. Tracked in docs/M4-Fleet-Health.md.