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/verbs.go

@@ -85,8 +85,12 @@ var ControllerVerbs = []Verb{
 		Input: schema(nil, nil)},
 	{Name: "seats", Description: "Every seat the mesh defines, what it delivers, and who holds it.",
 		Input: schema(nil, nil)},
-	{Name: "builds", Description: "What has been built lately and what came of it, for every module or for one.",
-		Input: schema(map[string]string{"module": "one module's name; every module when absent"}, nil)},
+	{Name: "builds", Description: "What has been built lately and what came of it, for every module or for one; " +
+		"or, given a build's id, everything the build machine said while building it, line by line, from the bus.",
+		Input: schema(map[string]string{
+			"module": "one module's name; every module when absent",
+			"log":    "a build's id (as `builds` lists it): print what the build machine said, line by line",
+		}, nil)},
 	{Name: "plan", Description: "What one machine would run, and why: the declaration the mesh would send it.",
 		Input: schema(map[string]string{"node": "the machine's name"}, []string{"node"})},
 	{Name: "assign", Description: "Put a module on a machine. Refused with the mesh's own words when it cannot resolve there.",