ADR 0157: a build says what it does on the bus, as it happens; designs 25 and 18 carry it

03-DESIGN/01-to-be/18-building-a-module.md

@@ -5,8 +5,9 @@ code:
   - mesh-controller cmd/mesh-builder
   - mesh-controller internal/builder
   - mesh-catalog modules/builder
-updated: 2026-09-30
+updated: 2026-10-01
 decisions:
+  - 02-DECISIONS/0157-a-build-says-what-it-does-on-the-bus-as-it-happens.md
   - 02-DECISIONS/0150-a-modules-own-code-runs-as-supervised-processes-under-one-account.md
   - 02-DECISIONS/0142-the-mesh-delivers-its-own-components-as-binaries.md
   - 02-DECISIONS/0111-a-build-source-is-on-the-git-seat-or-external.md
@@ -267,6 +268,28 @@ ships one and wrong for code the mesh built, which has no unit until the mesh wr
 **Tools, hooks and consumers are not further modes**, which is the test of whether three is the
 right number: they are loaded by a tool host, and a tool host is a process that stays up.
 
+## A build says what it does, as it happens
+
+*2026-10-01 — [ADR 0157](../../02-DECISIONS/0157-a-build-says-what-it-does-on-the-bus-as-it-happens.md).*
+
+A build machine narrates every build on the bus as the role it holds: `started` when it takes the
+work, one `log.<build id>` event per line — every command it runs with its duration, every step of
+the recipe, and on failure the command's own output, line by line — and `built` for the outcome as
+before. The same lines still go to the machine's standard error, so a build machine with nobody
+listening is as readable as it was; a listener reads the same lines, live, from anywhere on the mesh.
+
+One build is one subject. A reader follows it by subscribing that subject and nothing else, and the
+events stream keeps it for a week, so `builds --log <id>` — on the command line and as the
+controller's seat verb through the console — reads it back afterwards. `builds` lists every build's
+id beside it, and `build` says the id it asked with. The mesh keeps no second copy: the stream is the
+log. A viewer of builds, when one is built, is a subscriber over these subjects and the outcome; the
+builder needs nothing more for it.
+
+*How it is checked:* the holder's grant is exactly `started`, `built` and `log.*` (broker test); a
+build's lines reach a reader of its subject in order and the stream holds them afterwards (link test
+against a real server); the seat verb with an id reads the log (controller test); and, live, a build
+after the roll-out read line by line through the console.
+
 ## The builder compiles the languages the mesh is written in
 
 *2026-09-29 —

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

@@ -7,8 +7,9 @@ code:
   - mesh-tools src/broker-amqp.ts (to be replaced)
   - mesh-catalog modules/nats (to be written)
   - mesh-sdk src (the protocol's NATS binding, step 3)
-updated: 2026-09-27
+updated: 2026-10-01
 decisions:
+  - 02-DECISIONS/0157-a-build-says-what-it-does-on-the-bus-as-it-happens.md
   - 02-DECISIONS/0106-the-bus-is-nats.md
   - 02-DECISIONS/0131-everything-on-the-mesh-speaks-to-the-broker-seat.md
   - 02-DECISIONS/0116-the-bus-is-built-in-five-steps.md
@@ -135,7 +136,7 @@ Core NATS is at-most-once. Everything the mesh must not lose lives in a JetStrea
 |---|---|---|---|
 | CONTROL | `mesh.control.>` except `alive` (a build's outcome moved to its seat, ADR 0121) | work queue, one consumer (the controller), explicit ack | the store-window guarantee ([ADR 0083](../../02-DECISIONS/0083-one-push-leaves-the-mesh-consistent.md)): the controller `nak`s with a delay while its store is away and the message is redelivered; nothing is dropped |
 | NODES | `mesh.node.>` | last per subject | one declaration per node, always the newest |
-| EVENTS | `mesh.mod.*.event.>` | limits (age, size), durable consumer per subscribing module | a subscriber that was down catches up; after `max-deliver` attempts the advisory feeds `mesh.events.dead` (its own small stream) |
+| EVENTS | `mesh.mod.*.event.>` and `mesh.seat.*.event.>` | limits (age, size), durable consumer per subscribing module | a subscriber that was down catches up; after `max-deliver` attempts the advisory feeds `mesh.events.dead` (its own small stream). *2026-10-01:* a build's whole log is here too, as the build-machine seat's `log.<build id>` events ([ADR 0157](../../02-DECISIONS/0157-a-build-says-what-it-does-on-the-bus-as-it-happens.md)) — one subject per build, a week of retention, read back by `builds --log <id>` with a consumer that is gone when the reading is done |
 
 Tool calls and heartbeats stay on core NATS: a lost heartbeat is the next heartbeat; a lost tool
 call is a timeout the caller already handles.