Delete the builder, the build asks, the build queue and the merge gate: the builder's keys are the only way a module is built (issues 1851, 1299, 1318; C2b-C5, C10)

The controller asks no build of anybody (ADR 0501 §5, ADR 0525 clause 6, ADR 0503 §3). Every module of a walk is taken from the
builder's done key; a key not done yet waits, named in the plan, and never fails it.

- C2b/C2c: internal/builder and cmd/mesh-controller's asks go (askABuild, onlyTheBuildersOwn, buildOneAsked, takeIn from an
  outcome, buildAgentsOwn, the builder's say and its fallback, the daemon hearing an outcome). The server follows the retired
  seats' built subjects only to let go of them, because the installer's carried user list names them.
- C2d: replay, queue, cancel, clear, kill, pause, resume, delivery-check, check-here and merge-gate are refused by name.
- C3: the check queues (CHECKS_READY, CHECKS_OTHER) and their workers, the checks-running and plans-building buckets and
  their grants, the build queue and its hold (plans_building.go, queue.go, link/holds.go, builds_nats.go, checks_nats.go).
- C4: merge_gate*.go, the pull request's repo-check path, the Checked event and its layers; a pull request asks the
  controller nothing but to tell mesh-config what its head declares.
- C5: the builds bucket is written only by key_takein.
- C10 (help and refusals): the terminal's help lists only what is served.

Integration tests of the plan's tiers, sends, stops and retries now run on a stand-in builder with a done key for every
module (walk_keys_scaffold_integration_test.go); the tests of the asks, the queue, the merge gate and the replays are deleted.

cmd/mesh-controller/signals.go

@@ -62,10 +62,6 @@ const (
 	tierAtLeast = planWaitBound
 	// loopDeafAfter is how long the event loop may take nothing while its consumers hold some (S4).
 	loopDeafAfter = 2 * time.Minute
-	// askAtLeast is the least a build ask is given, and askDefault the bound while nothing is
-	// measured (S6): the build seat declares no timeout of its own.
-	askAtLeast = 20 * time.Minute
-	askDefault = time.Hour
 	// callDefault is the bound of a verb that declares none (S7); push's and build's are longer.
 	callDefault = 10 * time.Minute
 	// advisoryQuiet is how long the bus must be quiet about a thing before its advisory clears (S9).
@@ -114,9 +110,8 @@ var signalsTable = []signalRow{
 			return newestOf(f.machines, func(m machineFacts) time.Time { return m.reportedAt })
 		}},
 	{Row: "S3", Signal: "plan tier progress", Emitter: "controller's plan", Trigger: "each tier entered",
-		Bound: "max(30 min, 3 × the p90 of that repository's measured tiers), provisional; not while the " +
-			"build seat is paused under it",
-		Kind: "stalled", Severity: conditions.Warning, Phase: 1,
+		Bound: "max(30 min, 3 × the p90 of that repository's measured tiers), provisional",
+		Kind:  "stalled", Severity: conditions.Warning, Phase: 1,
 		needs: func(f *signalFacts) error { return f.plansErr }, watch: watchPlans,
 		newest: func(f *signalFacts) time.Time {
 			return newestOf(f.plans, func(p planFacts) time.Time { return p.entered })
@@ -126,12 +121,6 @@ var signalsTable = []signalRow{
 		Kind: "controller-deaf", Severity: conditions.Urgent, Phase: 1,
 		needs: func(f *signalFacts) error { return f.loopErr }, watch: watchLoop,
 		newest: func(f *signalFacts) time.Time { return f.loop.took }},
-	{Row: "S6", Signal: "a build asked → its outcome", Emitter: "build seat", Trigger: "each ask",
-		Bound: "max(20 min, 3 × the p90 of measured builds), 1 h while nothing is measured, provisional — the " +
-			"build seat declares no timeout; and an ask the queue gave up on (dead) at once",
-		Kind: "ask-lost", Severity: conditions.Warning, Phase: 1,
-		needs: func(f *signalFacts) error { return f.asksErr }, watch: watchAsks,
-		newest: func(f *signalFacts) time.Time { return newestOf(f.asks, func(a askFacts) time.Time { return a.since }) }},
 	{Row: "S7", Signal: "a call running → finished", Emitter: "controller", Trigger: "each call",
 		Bound: "the verb's bound: push, rotate and command 30 min, assign and unassign 15 min, doctor 3 min, " +
 			"any other 10 min",
@@ -407,9 +396,9 @@ func watchReports(f *signalFacts) []conditions.Observation {
 func watchPlans(f *signalFacts) []conditions.Observation {
 	var out []conditions.Observation
 	for _, p := range f.plans {
-		// Under a paused build seat, or held only by the bus's planned step (S17, novox/hq issue 336): a wait
+		// Held only by the bus's planned step (S17, novox/hq issue 336): a wait
 		// for a person, said as itself, not a walk running late.
-		if p.paused || p.bus {
+		if p.bus {
 			continue
 		}
 		in := f.now.Sub(p.entered)
@@ -521,32 +510,6 @@ func watchLoop(f *signalFacts) []conditions.Observation {
 		Said: fmt.Sprintf("%d pending (%s), last taken %s", f.loop.pending, f.loop.where, since.UTC().Format(time.RFC3339))}}
 }
 
-func watchAsks(f *signalFacts) []conditions.Observation {
-	var out []conditions.Observation
-	for _, a := range f.asks {
-		var said string
-		switch {
-		case a.state == link.AskDead:
-			said = fmt.Sprintf("the %s queue handed it out as often as it may and it was never settled", a.seat)
-		case a.state == link.AskInFlight && f.now.Sub(a.since) > a.bound:
-			said = fmt.Sprintf("in flight on %s for %s (bound %s)", orSomewhere(a.on), ago(f.now.Sub(a.since)), ago(a.bound))
-		default:
-			continue
-		}
-		out = append(out, conditions.Observation{Scope: conditions.ScopeBuild, ID: a.id, Kind: "ask-lost",
-			Token: "lost", Machine: a.on, Severity: conditions.Warning,
-			Summary: fmt.Sprintf("the build %s of %s has no outcome: %s", a.id, a.what, said), Said: said})
-	}
-	return out
-}
-
-func orSomewhere(node string) string {
-	if node == "" {
-		return "a machine that did not say which"
-	}
-	return node
-}
-
 func watchCalls(f *signalFacts) []conditions.Observation {
 	var out []conditions.Observation
 	for _, c := range f.calls {
@@ -738,8 +701,6 @@ func consumerWho(stream, consumer string) string {
 	switch {
 	case consumer == broker.ControllerName || consumer == broker.MergesConsumerName:
 		return "the controller"
-	case broker.IsCheckStream(stream):
-		return "the holder of " + broker.TheBuildSeat
 	case strings.HasPrefix(stream, "SEAT_") && strings.HasSuffix(consumer, "_worker"):
 		seat := strings.ToLower(strings.ReplaceAll(strings.TrimSuffix(strings.TrimPrefix(consumer, "SEAT_"), "_worker"), "_", "-"))
 		return "the holder of " + seat