A build says what it does on the bus, as it happens (novox/hq ADR 0157)

The build-machine seat emits `started` and `log.<build id>` beside `built`. Every line the builder
speaks — each step, each command with its duration, and on failure the command's own output — goes
to stderr as before and onto the bus under the build's id, one subject per build, kept a week in
EVENTS with every other event. `builds --log <id>` reads it back from the stream with a consumer
that is gone when the reading is done, on the command line and as the controller's seat verb;
`builds` lists each build's id and `build` says the id it asked with.

Lines are core publishes with a sequence number, so a build is not slowed by an ack per line and a
gap is visible; `started` and `built` are awaited into the stream. The seat protocol widens
additively at the controller's next start; the holder's grant follows on the broker node's next
composition.

internal/catalogue/seats.go

@@ -80,8 +80,11 @@ var defaultSeats = []Seat{
 	// A build is work submitted to this role and its outcome is the role's own event (ADR 0129).
 	// One publish reaches whoever asked, the controller that records it, and the catalogue that
 	// places it in the graph — what the old bus's shared exchange did for free.
+	// A build says what it does as it does it (novox/hq ADR 0157): `started` when work is taken,
+	// `log.<build id>` for every line, `built` for the outcome. The log's tail token is the build's
+	// id, so a reader follows one build by subject alone.
 	{Name: "mesh-build-machine", Scope: ScopeMesh,
-		Accepts: []string{"build"}, Emits: []string{"built"}, Decision: "novox/hq ADR 0121"},
+		Accepts: []string{"build"}, Emits: []string{"started", "built", "log.*"}, Decision: "novox/hq ADR 0121"},
 	{Name: "node-dns-resolver", Scope: ScopeNode, Decision: "novox/hq ADR 0121"},
 	{Name: "node-intrusion-prevention", Scope: ScopeNode, Decision: "novox/hq ADR 0121"},
 	{Name: "node-packet-filter", Scope: ScopeNode, Decision: "novox/hq ADR 0121"},