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.

00-META/checks/records.py

@@ -299,8 +299,11 @@ def check_progressive_insights(failures, records):
     unmarked change stands out as the anomaly it is.
     """
     phrase = re.compile(r"progressive insight", re.I)
-    marker = re.compile(r"\*\*Progressive insights?\s*[\u2014\u2013-]\s*(\d{4}-\d{2}-\d{2})\.?\*\*")
+    # Both patterns stay on one line: a bold run does not span paragraphs, and `[^*]*` across
-    loose = re.compile(r"\*\*[^*]*[Pp]rogressive insights?[^*]*\*\*")
+    # newlines will happily join an unrelated `**` far above to the marker below, reporting the
+    # whole span between them. It did exactly that the first time this ran.
+    marker = re.compile(r"\*\*Progressive insights?[ \t]*[\u2014\u2013-][ \t]*(\d{4}-\d{2}-\d{2})\.?\*\*")
+    loose = re.compile(r"\*\*[^*\n]*[Pp]rogressive insights?[^*\n]*\*\*")
     iso = re.compile(r"^\d{4}-\d{2}-\d{2}$")
 
     for number, record in sorted(records.items()):

02-DECISIONS/0106-the-bus-is-nats.md

@@ -75,6 +75,19 @@ after its deliveries are exhausted; a module's account cannot publish outside it
 subscribe outside its `consumes`. Then the cutover bed: a mesh on AMQP with the predecessor's
 compatibility broker beside it moves its bus in one rollout with every node reporting afterwards.
 
+## Progressive insight
+
+> **Progressive insight — 2026-09-26.** *The compatibility broker was not single-purpose when this
+> was written.* This record says the adopted AMQP broker is "kept as a module with one purpose —
+> the predecessor's clients". Two modules of the new mesh also depended on it, through a `requires:
+> ["amqp"]` grant its provisioner answered with a private vhost — `amqp-ping` and
+> `amqp-email-forwarder`. On the retirement condition below, both would have been left requiring
+> something no provider answers.
+> [ADR 0117](0117-the-bus-is-the-only-broker.md) resolves it by moving them onto the bus and
+> retiring the interface, which makes this record's sentence true rather than merely intended. The
+> decision — the bus is NATS, the AMQP broker becomes the predecessor's compatibility broker and
+> retires with the last of them — is unchanged.
+
 ## References
 
 - [research 014](../01-RESEARCH/014-the-bus-on-nats/00-overview.md)

02-DECISIONS/0117-the-bus-is-the-only-broker.md

@@ -0,0 +1,132 @@
+---
+topic: the mesh
+status: accepted
+date: 2026-09-26
+deciders: jochen
+reconstructed: false
+extends: 02-DECISIONS/0106-the-bus-is-nats.md
+---
+
+# 117. The bus is the only broker
+
+## Context
+
+[ADR 0106](0106-the-bus-is-nats.md) moved the mesh's bus to NATS and kept the AMQP broker "as a
+module with one purpose — the predecessor's clients", retiring with the last of them.
+[Design 25](../03-DESIGN/01-to-be/25-the-bus-on-nats.md) repeats that: a compatibility module with
+a single purpose and a retirement condition.
+
+**It is not single-purpose, and was not when that was written.** Two modules of the *new* mesh
+declare `requires: ["amqp"]` and are answered by the broker module's own provisioner:
+
+- `amqp-ping`, whose source says it "exists to PROVE the grant end to end: the mesh gave it a
+  scoped login and a vhost of that name on the lavinmq provider";
+- `amqp-email-forwarder`, which uses it for work.
+
+What that provisioner answers is **not the mesh's bus**. Its own comment draws the line: a
+consumer gets "its own message broker, isolated from every other consumer's by the vhost
+boundary… a broker of its own, not a shared account on the mesh's control-plane broker" —
+vhost-per-login, "the exact analog of postgres's database-per-login."
+
+So two different things wear the word *broker*: the mesh's nervous system, and a private message
+broker handed to a module as a resource, the way a database is. The first is being replaced. The
+second was never examined, and on the retirement condition ADR 0106 sets, it disappears with no
+successor and nothing notices — a module of the new mesh left requiring something no provider
+answers.
+
+The operator's direction, asked at the point this surfaced: **NATS is the heart of the
+application** — not a component it contains, and not a thing to reproduce the predecessor's
+shapes on.
+
+## Considered Options
+
+1. **Carry the private broker forward onto NATS** — each requiring module gets its own NATS
+   account, provisioned like a database. Rejected on three counts. It reproduces the
+   predecessor's shape on the new bus, which is the thing this whole move exists to stop. It
+   gives the mesh two messaging models, so "how does a module send a message" has two answers
+   depending on a manifest line. And NATS accounts isolate subject spaces *entirely*: a module
+   inside its own account cannot reach the mesh's bus at all, so it would hold two connections
+   and two identities to do one job.
+2. **Keep the compatibility broker indefinitely** for the mesh's own modules. Rejected: its
+   retirement condition is the point of it. A module of the new mesh depending on the retired one
+   keeps the predecessor alive permanently, which is the opposite of a compatibility module.
+3. **One bus. A module's messaging is subjects on it, scoped by what it declares.** Adopted.
+
+## Decision
+
+**The bus is the only broker.** NATS is the mesh's one messaging system, and every module's
+messaging is subjects on that bus under its own account, scoped by its `emits` and `consumes`
+([ADR 0043](0043-a-module-broker-account-is-scoped-by-emits-and-consumes.md)). There is no second
+broker, and none is handed to a module as a resource.
+
+**The `amqp` interface is not carried forward.** It leaves the set of things a module may require
+and retires with the compatibility broker rather than gaining a successor.
+
+Concretely, in the controller's seat table: **the `mesh-broker` seat delivers nothing.** It
+currently reads `Delivers: "amqp"` — the seat's holder answers a requirement for a broker — and
+under this decision it joins `mesh-controller` and `the-catalogue`, the foundation seats that
+deliver no provision at all. The bus is not something a module asks for; it is what a module is
+reached through.
+
+- `amqp-email-forwarder` moves to the bus like any module: what it emits and consumes, declared,
+  and the account follows.
+- `amqp-ping`'s *purpose* is kept and its mechanism is not. Proving end to end that a module
+  receives scoped messaging it did not configure itself is worth a probe; it becomes a probe of
+  the bus, and its assertion changes from "I reached my own vhost" to "I reached exactly my
+  subjects and was refused the rest."
+
+**A module that wants a queue of its own has one already**: a subject nothing else may publish to
+and a durable consumer of its own, both derived from its declaration. What it does not get is a
+server of its own.
+
+**The mesh's own streams are the controller's, created at genesis, not provisioned** — and
+`EVENTS` is one stream, closing the question [design 25](../03-DESIGN/01-to-be/25-the-bus-on-nats.md)
+§11 left open. The reason is not preference but **bootstrapping**: a provisioner is a module, and
+a module needs a bus account before it can run at all. Anything the bus itself is made of must
+exist before the first module starts, so it is composed as configuration
+([ADR 0106](0106-the-bus-is-nats.md): never through a management API) rather than provisioned by
+something that could not yet be running.
+
+## Consequences
+
+- **Design 25 gains the distinction and loses the "single purpose" claim**; its §11 question about
+  the `EVENTS` stream closes here.
+- **Nothing in [design 27](../03-DESIGN/01-to-be/27-a-module-requires-the-mesh-resolves.md)'s
+  model changes** — the four provider kinds, the contract, resolution all stand, and it never
+  enumerated interfaces, so there is nothing to strike from it. What changes is that messaging
+  leaves the set of things resolved at all: every module has it by existing.
+- **One line of the controller's seat table changes**, and it is the load-bearing one:
+  `mesh-broker` stops declaring what it delivers. A requirement for `amqp` then resolves to
+  nothing and is refused at assignment, which is how the two modules below are found rather than
+  discovered at runtime.
+- **Two modules have conversion work**, and it belongs to step 4 of
+  [ADR 0116](0116-the-bus-is-built-in-five-steps.md), with the flows. Neither blocks step 1.
+- **The compatibility broker becomes what ADR 0106 already called it** — single-purpose — once
+  those two have moved. That record's claim was wrong when written and is made true by this one.
+- **What got harder:** a module that genuinely wanted an isolated server — a tenant boundary at
+  the broker rather than at the subject — no longer has that option, and would have to argue for
+  it as a new decision. That is the intended cost: one bus is the point.
+
+## How it is checked
+
+- **A module's messaging works with no `requires` line for it.** A lab bed: a module declaring
+  only `emits` and `consumes` reaches its subjects, and is refused every other — which is
+  [ADR 0116](0116-the-bus-is-built-in-five-steps.md) step 1's permission bed, already required.
+- **Nothing requires `amqp`.** With the seat delivering nothing, a module still declaring it is
+  refused at resolution — the existing "requirement no provider answers" path, not a new check. A
+  catalogue test asserts no module declares it once the two have moved.
+- **The probe proves the claim it is named for.** `amqp-ping`'s successor fails if a module can
+  reach a subject outside its declaration, not merely if it cannot reach its own.
+- **The compatibility broker's retirement condition can actually be met.** A check that no module
+  of the mesh — as opposed to a predecessor client — holds a connection to it.
+
+## References
+
+- [ADR 0106](0106-the-bus-is-nats.md) — the bus is NATS; corrected here on what the compatibility
+  broker serves.
+- [ADR 0116](0116-the-bus-is-built-in-five-steps.md) — the steps; the conversions land in step 4.
+- [ADR 0043](0043-a-module-broker-account-is-scoped-by-emits-and-consumes.md) — the scoping that
+  makes one bus safe.
+- [design 25](../03-DESIGN/01-to-be/25-the-bus-on-nats.md),
+  [design 27](../03-DESIGN/01-to-be/27-a-module-requires-the-mesh-resolves.md) — the two documents
+  this changes.

02-DECISIONS/README.md

@@ -133,6 +133,7 @@ python3 00-META/checks/index.py            fail if stale
 - **0105** — [The mesh adopts the predecessor's tunnel in place](0105-the-mesh-adopts-the-predecessors-tunnel-in-place.md)
 - **0106** — [The bus is NATS](0106-the-bus-is-nats.md)
 - **0116** — [The bus is built in five steps, and the protocol moves with it](0116-the-bus-is-built-in-five-steps.md)
+- **0117** — [The bus is the only broker](0117-the-bus-is-the-only-broker.md)
 
 ### Its tiers, from the bottom up
 

03-DESIGN/01-to-be/25-the-bus-on-nats.md

@@ -1,6 +1,6 @@
 ---
 layer: to-be
-status: proposed
+status: in-progress
 code:
   - mesh-controller internal/link (to be replaced)
   - mesh-host internal/link (to be replaced)
@@ -10,6 +10,7 @@ code:
 updated: 2026-09-26
 decisions:
   - 02-DECISIONS/0106-the-bus-is-nats.md
+  - 02-DECISIONS/0117-the-bus-is-the-only-broker.md
   - 02-DECISIONS/0116-the-bus-is-built-in-five-steps.md
   - 02-DECISIONS/0074-the-wire-is-specified-not-the-types.md
   - 02-DECISIONS/0079-the-foundation-seats-are-named-after-their-servers.md
@@ -188,8 +189,19 @@ current. Nothing is declared as `reload-on` or `restart-on` for this resource at
 
 Its guard is the same rule as the AMQP broker's: the monitoring port is refused from anything but
 the private network. It is raised at genesis like the store, adopted as a module in the same
-phase. The predecessor's AMQP broker remains a module of its own, `lavinmq-compat`, with a single
+phase. The predecessor's AMQP broker remains a module of its own, `lavinmq-compat`, with a
-purpose and a retirement condition: no client connected for a period the operator sets.
+retirement condition: no client connected for a period the operator sets.
+
+**And with one purpose, which it did not have when this was written.** Revision, second review
+([ADR 0117](../../02-DECISIONS/0117-the-bus-is-the-only-broker.md)): two modules of the new mesh
+required a broker *of their own* from it — a private vhost per consumer, the analog of
+database-per-login, which is a different thing from the mesh's bus and was never examined here.
+**There is one bus, and no module is handed a broker as a resource.** A module's messaging is
+subjects on the bus under its own account, scoped by its `emits` and `consumes`; a module that
+wants a queue of its own has a subject nothing else may publish to and a durable consumer, both
+from its declaration. What it does not get is a server of its own. The `amqp` interface retires
+with the compatibility broker instead of gaining a successor, and the two modules move to the bus
+in step 4.
 
 ## 6. Joining: the enrolment handshake
 
@@ -398,8 +410,11 @@ find what changed and why.
 
 **Still open:**
 
-- Whether EVENTS should be one stream or one per emitting module (retention per module vs. one
+- ~~Whether EVENTS should be one stream or one per emitting module.~~ **Closed**
-  policy). One stream is proposed; the review may disagree.
+  ([ADR 0117](../../02-DECISIONS/0117-the-bus-is-the-only-broker.md)): one stream, and not as a
+  preference — the streams the bus is made of are composed as configuration before any module
+  runs, because a provisioner is itself a module that needs a bus account to start. Bootstrapping
+  decides it.
 - The heartbeat interval and the controller's "quiet" threshold on core NATS without persistence —
   the same numbers as today are proposed.
 - Whether the person's client is a catalogue module (runs on an enrolled workstation node) or a

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

@@ -1,11 +1,15 @@
 ---
 layer: to-be
-status: proposed
+status: in-progress
-code: []
+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