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.

cmd/mesh-controller/seatverbs.go

@@ -62,6 +62,9 @@ func argvFor(verb string, args map[string]any) ([]string, error) {
 	case "seats":
 		return []string{"seats", "--json"}, nil
 	case "builds":
+		if id := str("log"); id != "" {
+			return []string{"builds", "--log", id}, nil
+		}
 		if m := str("module"); m != "" {
 			return []string{"builds", m}, nil
 		}