ADR 0122: the predecessor is ending, and its broker goes with it

ADR 0119 rejected giving the old broker a retirement condition and said why: "its
clients are not only the predecessor's, so the retirement condition describes a day
that will not come". The operator has said that day is coming — the predecessor is
deprecated, some of it still running, none of it being migrated, left to stop rather
than moved.

Recorded because three documents reason from the premise it overturns. Design 25 §5's
"no day anything is waiting for", §9's "the predecessor's clients never notice", and
design 28's closing note that the predecessor's world does not need to move.

**And it needs no new machinery, which is 0119 being paid off rather than revised.**
Because that record made the broker an ordinary provider rather than a compatibility
module, ending it is unassigning a provider whose provision nothing requires — something
the module system has done since it existed. So step 5.3 finishes instead of trailing
off, and the transitional double announcement of a build outcome has a date.

The consequence worth planning around: the predecessor's own mesh talks over that
broker, so shutting it down ends the tooling that reaches this installation's machines
from a workstation. The rollout is driven from the node, or driven before the broker
stops. That is a sequencing constraint on 5.2, not an afterthought.

What survives is `amqp` as a provision: a module that genuinely needs an AMQP broker can
still be given one. What retires is this broker's role as the predecessor's.

02-DECISIONS/README.md

@@ -137,6 +137,7 @@ python3 00-META/checks/index.py            fail if stale
 - **0119** — [AMQP is a provision, not the bus](0119-amqp-is-a-provision-not-the-bus.md)
 - **0120** — [The mesh bus is required, not ambient](0120-the-mesh-bus-is-required-not-ambient.md)
 - **0121** — [A seat carries the protocol of its role](0121-a-seat-carries-the-protocol-of-its-role.md)
+- **0122** — [The predecessor is ending, and its broker goes with it](0122-the-predecessor-is-ending-and-its-broker-goes-with-it.md)
 
 ### Its tiers, from the bottom up