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_test.go

@@ -30,6 +30,18 @@ func TestEveryDeclaredVerbHasACommandLine(t *testing.T) {
 	}
 }
 
+// `builds` given a build's id reads that build's log from the bus rather than listing builds
+// (novox/hq ADR 0157).
+func TestBuildsWithAnIdReadsThatBuildsLog(t *testing.T) {
+	argv, err := argvFor("builds", map[string]any{"log": "build-17"})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if strings.Join(argv, " ") != "builds --log build-17" {
+		t.Fatalf("builds with a log id became %q", strings.Join(argv, " "))
+	}
+}
+
 // A required argument missing is refused in the verb's own words, before anything runs.
 func TestAVerbMissingWhatItNeedsIsRefused(t *testing.T) {
 	if _, err := argvFor("node", map[string]any{}); err == nil || !strings.Contains(err.Error(), `node needs "node"`) {