The bus is the only broker; step 1 starts

A module does declare requirements the provisioner fulfils — but the broker
it gets that way is a private vhost, the analog of a database, not the
mesh's bus. Two modules of the new mesh depend on it, so the compatibility
broker was never single-purpose and its retirement would have stranded them.

NATS is the heart: one bus, a module's messaging is subjects on it scoped by
what it declares, and no module is handed a server of its own. The seat
delivers nothing; the interface retires with the broker. Also closes the
EVENTS question — one stream, on the bootstrap argument, not preference.

Designs 25 and 28 go in-progress: step 1 is starting.

The insight check caught a false positive on its own first real use — its
bold-run pattern crossed newlines and joined an unrelated `**` to the
marker. Constrained to one line, still catching all four bad shapes.

03-DESIGN/01-to-be/28-building-the-bus.md

@@ -1,11 +1,15 @@
 ---
 layer: to-be
-status: proposed
-code: []
+status: in-progress
+code:
+  - mesh-catalog modules/nats
+  - mesh-controller internal/catalogue
+  - mesh-lab scenarios
 updated: 2026-09-26
 decisions:
   - 02-DECISIONS/0116-the-bus-is-built-in-five-steps.md
   - 02-DECISIONS/0106-the-bus-is-nats.md
+  - 02-DECISIONS/0117-the-bus-is-the-only-broker.md
   - 02-DECISIONS/0074-the-wire-is-specified-not-the-types.md
   - 02-DECISIONS/0079-the-foundation-seats-are-named-after-their-servers.md
   - 02-DECISIONS/0100-a-node-in-use-is-adopted-before-it-is-converged.md