diff --git a/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/bus.go b/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/bus.go
index b456fbd..359b1e9 100644
--- a/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/bus.go
+++ b/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/bus.go
@@ -102,43 +102,6 @@ func follow(ctx context.Context, w jetstream.KeyWatcher, each func(jetstream.Key
 	}
 }
 
-// stepsWaiter waits for a build module's step by watching its key in the module's steps bucket (ADR 0469 clause 2): the
-// watch hands over the value the key holds now, so a step that ended before the watch began is read at once, and every
-// change after. No timer: the caller bounds the wait with its context.
-type stepsWaiter struct{ js bucketOpener }
-
-func (w stepsWaiter) Wait(ctx context.Context, module, key string) (delivery.Step, error) {
-	kv, err := w.js.KeyValue(ctx, delivery.StepsBucket(module))
-	if err != nil {
-		return delivery.Step{}, fmt.Errorf("the bucket %s: %w", delivery.StepsBucket(module), err)
-	}
-	watch, err := kv.Watch(ctx, key)
-	if err != nil {
-		return delivery.Step{}, err
-	}
-	defer watch.Stop()
-	for {
-		select {
-		case <-ctx.Done():
-			return delivery.Step{}, ctx.Err()
-		case e, ok := <-watch.Updates():
-			if !ok {
-				return delivery.Step{}, errors.New("the watch of the step ended")
-			}
-			if e == nil || !opOf(e) {
-				continue
-			}
-			step, err := delivery.DecodeStep(e.Value())
-			if err != nil {
-				return delivery.Step{}, fmt.Errorf("the step %s is not a step: %w", key, err)
-			}
-			if step.State != delivery.StepRunning {
-				return step, nil
-			}
-		}
-	}
-}
-
 // manifestReader reads manifests.<digest> of the indexer and parses the manifest it holds.
 type manifestReader struct{ kv jetstream.KeyValue }
 
diff --git a/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/integration_test.go b/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/integration_test.go
index 182885b..d7d0faa 100644
--- a/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/integration_test.go
+++ b/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/integration_test.go
@@ -22,6 +22,7 @@ import (
 	"github.com/nats-io/nats.go"
 	"github.com/nats-io/nats.go/jetstream"
 
+	"git.novox.be/novox/mesh-sdk/go/buildstep"
 	"git.novox.be/novox/mesh-sdk/go/delivery"
 )
 
@@ -47,13 +48,12 @@ const (
 	fp     = "src2:3333333333333333333333333333333333333333333333333333333333333333"
 )
 
-// fakeBuildModules serve the tools of mesh-build-go and mesh-build-node as the real ones do (ADR 0469 clause 2): a call on
-// mesh.mod.<module>.call.<tool>.<node>.<caller> answers at once with the step and its key, and the step's end is written to
-// the key <node>.<id> of the module's steps bucket, some milliseconds later.
+// fakeBuildModules are the build modules on the nodes as the real ones run since R4g (ADR 0525; issue 1887 A4): each pulls
+// its build seat's asks on its nodes (buildstep.Puller over the seat's workers) and runs an ask's job with step bodies that
+// answer as the real tools do, ending the step on <node>.<ask id> of its steps bucket.
 type fakeBuildModules struct {
 	js        jetstream.JetStream
 	ctx       context.Context
-	n         atomic.Int64
 	failBuild atomic.Bool
 	// refusePush makes every bundle and archive build fail as a push the artifact store refused (ADR 0498 clause 2).
 	refusePush atomic.Bool
@@ -75,76 +75,68 @@ func digestOf(artifact string) string {
 	return "sha256:" + hex.EncodeToString(sum[:])
 }
 
-func (f *fakeBuildModules) serve(t *testing.T, nc *nats.Conn, module string) {
-	steps, err := f.js.CreateKeyValue(f.ctx, jetstream.KeyValueConfig{Bucket: delivery.StepsBucket(module), History: 1})
+var prefixOf = map[string]string{"mesh-build-go": "build_go_", "mesh-build-node": "build_node_", "mesh-build-image": "build_image_"}
+
+// step is one tool's answer, as the real module's.
+func (f *fakeBuildModules) step(module, name string, args map[string]any) (any, error) {
+	tool := prefixOf[module] + name
+	f.mu.Lock()
+	f.calls[module+"."+tool]++
+	if name == "fetch" {
+		f.fetches = append(f.fetches, args)
+	} else {
+		f.builds = append(f.builds, args)
+	}
+	f.mu.Unlock()
+	switch {
+	case name == "fetch":
+		merge := ""
+		if args["base"] != nil { // a fetch with a base answers the merge commit (mesh-build-go FetchResult)
+			merge = `,"merge":"` + strings.Repeat("9", 40) + `"`
+		}
+		return json.RawMessage(`{"workspace":"w` + buildstep.NewID() + `","commit":"` + commit + `"` + merge + `}`), nil
+	case f.failBuild.Load() && tool != "build_image_copy": // the build fails wherever it runs
+		return nil, fmt.Errorf("go build of %v: boom", args["artifact"])
+	case tool == "build_image_copy": // the upstream copy answers the digest and the registry's reference (ADR 0498 clause 4)
+		d := digestOf(fmt.Sprint(args["artifact"]))
+		return json.RawMessage(`{"artifact":"` + fmt.Sprint(args["artifact"]) + `","digest":"` + d + `","reference":"registry.example/` + fmt.Sprint(args["module"]) + `/` + fmt.Sprint(args["artifact"]) + `@` + d + `","pushed":true}`), nil
+	case tool != "build_image_build" && f.refusePush.Load():
+		return nil, fmt.Errorf("%s%v: the artifact store answered 507 Insufficient Storage", delivery.NotStored, args["artifact"])
+	case tool != "build_image_build": // a bundle or an archive is pushed and its reference answered (ADR 0498 clause 1)
+		d := digestOf(fmt.Sprint(args["artifact"]))
+		return json.RawMessage(`{"digest":"` + d + `","reference":"artifact-store://` + filepath.Base(fmt.Sprint(args["module"])) + `/` + fmt.Sprint(args["artifact"]) + `/blobs/` + d + `"}`), nil
+	case tool == "build_image_build" && args["publish"] == true: // a trunk image is pushed: the digest and the reference
+		d := digestOf(fmt.Sprint(args["artifact"]))
+		return json.RawMessage(`{"digest":"` + d + `","reference":"registry.example/imaged/server@` + d + `"}`), nil
+	default:
+		return json.RawMessage(`{"digest":"` + digestOf(fmt.Sprint(args["artifact"])) + `"}`), nil
+	}
+}
+
+// serve makes module's steps bucket and its build seat's stream and workers, and pulls its asks on nodes.
+func (f *fakeBuildModules) serve(t *testing.T, module string, nodes ...string) {
+	kv, err := f.js.CreateKeyValue(f.ctx, jetstream.KeyValueConfig{Bucket: delivery.StepsBucket(module), History: 1})
 	if err != nil {
 		t.Fatal(err)
 	}
-	sub, err := nc.Subscribe("mesh.mod."+module+".call.>", func(m *nats.Msg) {
-		tokens := strings.Split(m.Subject, ".") // mesh mod <module> call <tool> <node> <caller>
-		tool, node := tokens[4], tokens[5]
-		f.mu.Lock()
-		f.calls[module+"."+tool]++
-		f.mu.Unlock()
-		var args map[string]any
-		_ = json.Unmarshal(m.Data, &args)
-		if strings.HasSuffix(tool, "_fetch") {
-			f.mu.Lock()
-			f.fetches = append(f.fetches, args)
-			f.mu.Unlock()
-		} else {
-			f.mu.Lock()
-			f.builds = append(f.builds, args)
-			f.mu.Unlock()
-		}
-		id := fmt.Sprintf("s%d", f.n.Add(1))
-		key, _ := delivery.StepKey(node, id)
-		put := func(s delivery.Step) {
-			data, err := delivery.EncodeStep(s)
-			if err == nil {
-				_, err = steps.Put(f.ctx, key, data)
-			}
-			if err != nil {
-				t.Errorf("writing step %s: %v", key, err)
-			}
-		}
-		step := delivery.Step{ID: id, Tool: tool, Node: node, State: delivery.StepRunning, Started: time.Now().UTC()}
-		put(step)
-		answer, _ := json.Marshal(map[string]any{"result": map[string]any{"step": id, "key": key, "state": "running"}, "error": "", "node": node})
-		_ = m.Respond(answer)
-		go func() {
-			time.Sleep(30 * time.Millisecond)
-			step.Ended = time.Now().UTC()
-			switch {
-			case strings.HasSuffix(tool, "_fetch"):
-				merge := ""
-				if args["base"] != nil { // a fetch with a base answers the merge commit (mesh-build-go FetchResult)
-					merge = `,"merge":"` + strings.Repeat("9", 40) + `"`
-				}
-				step.State, step.Result = delivery.StepPassed, json.RawMessage(`{"workspace":"w`+id+`","commit":"`+commit+`"`+merge+`}`)
-			case f.failBuild.Load() && tool != "build_image_copy": // every node's build fails: one node builds a fingerprint
-				step.State, step.Reason = delivery.StepFailed, fmt.Sprintf("go build of %v: boom", args["artifact"])
-			case tool == "build_image_copy": // the upstream copy answers the digest and the registry's reference (ADR 0498 clause 4)
-				d := digestOf(fmt.Sprint(args["artifact"]))
-				step.State, step.Result = delivery.StepPassed, json.RawMessage(`{"artifact":"`+fmt.Sprint(args["artifact"])+`","digest":"`+d+`","reference":"registry.example/`+fmt.Sprint(args["module"])+`/`+fmt.Sprint(args["artifact"])+`@`+d+`","pushed":true}`)
-			case tool != "build_image_build" && f.refusePush.Load():
-				step.State, step.Reason = delivery.StepFailed, fmt.Sprintf("%s%v: the artifact store answered 507 Insufficient Storage", delivery.NotStored, args["artifact"])
-			case tool != "build_image_build": // a bundle or an archive is pushed and its reference answered (ADR 0498 clause 1)
-				d := digestOf(fmt.Sprint(args["artifact"]))
-				step.State, step.Result = delivery.StepPassed, json.RawMessage(`{"digest":"`+d+`","reference":"artifact-store://`+filepath.Base(fmt.Sprint(args["module"]))+`/`+fmt.Sprint(args["artifact"])+`/blobs/`+d+`"}`)
-			case tool == "build_image_build" && args["publish"] == true: // a trunk image is pushed: the digest and the reference
-				d := digestOf(fmt.Sprint(args["artifact"]))
-				step.State, step.Result = delivery.StepPassed, json.RawMessage(`{"digest":"`+d+`","reference":"registry.example/imaged/server@`+d+`"}`)
-			default:
-				step.State, step.Result = delivery.StepPassed, json.RawMessage(`{"digest":"`+digestOf(fmt.Sprint(args["artifact"]))+`"}`)
-			}
-			put(step)
-		}()
-	})
-	if err != nil {
+	language := strings.TrimPrefix(module, "mesh-build-")
+	if err := buildstep.DeclareAskWorkers(f.ctx, f.js, language, 30*time.Second); err != nil {
 		t.Fatal(err)
 	}
-	t.Cleanup(func() { _ = sub.Unsubscribe() })
+	put := func(key string, value any) (uint64, error) {
+		raw, _ := value.(json.RawMessage)
+		return kv.Put(f.ctx, key, raw)
+	}
+	call := func(name string) buildstep.StepFunc {
+		return func(ctx context.Context, args map[string]any) (any, error) { return f.step(module, name, args) }
+	}
+	steps := buildstep.AskSteps{Fetch: call("fetch"), Build: call("build"), Copy: call("copy")}
+	for _, node := range nodes {
+		p := &buildstep.Puller{Source: &buildstep.JetStreamAsks{JS: f.js, Language: language}, Language: language, Node: node, Put: put,
+			Capacity: func() int { return 2 }, PullWait: 200 * time.Millisecond,
+			Run: func(ctx context.Context, a delivery.StepAsk) (any, error) { return buildstep.RunAsk(ctx, steps, a) }}
+		go func() { _ = p.Pull(f.ctx) }()
+	}
 }
 
 type bed struct {
@@ -154,8 +146,6 @@ type bed struct {
 	candidates jetstream.KeyValue
 	builds     jetstream.KeyValue
 	tools      map[string]jetstream.KeyValue
-	presence   jetstream.KeyValue
-	have       jetstream.KeyValue
 	instances  jetstream.KeyValue
 	stop       func() // stops the builder started last
 	fake       *fakeBuildModules
@@ -228,20 +218,11 @@ func startBed(t *testing.T) *bed {
 	b.candidates = mk(delivery.CandidatesBucket, delivery.CandidatesHistory)
 	mk(delivery.ManifestsBucket, delivery.ManifestsHistory)
 	b.builds = mk(delivery.BuilderBuildsBucket, delivery.BuilderBuildsHistory)
-	presence := mk(delivery.PresenceBucket, delivery.PresenceHistory)
-	b.presence, b.have = presence, mk(delivery.HaveBucket, delivery.HaveHistory)
 	b.instances = mk(instancesBucket, 1)
-	for _, node := range []string{"n1", "n2"} {
-		b.setOnline(t, node, true)
-		for _, module := range []string{"mesh-build-go", "mesh-build-node"} {
-			b.setHealth(t, node, module, delivery.HealthOK)
-		}
-	}
 	b.fake = &fakeBuildModules{js: js, ctx: ctx, calls: map[string]int{}}
-	b.fake.serve(t, ctl, "mesh-build-go")
-	b.fake.serve(t, ctl, "mesh-build-node")
-	b.fake.serve(t, ctl, "mesh-build-image")
-	b.setHealth(t, "n1", "mesh-build-image", delivery.HealthOK) // the image build module runs on n1 only
+	b.fake.serve(t, "mesh-build-go", "n1", "n2")
+	b.fake.serve(t, "mesh-build-node", "n1", "n2")
+	b.fake.serve(t, "mesh-build-image", "n1") // the image build module runs on n1 only
 	b.report(t, "mesh-build-go", "n1", "go", "go1.27.1", "1")
 	b.report(t, "mesh-build-go", "n2", "go", "go1.27.1", "1")
 	b.report(t, "mesh-build-node", "n1", "typescript", "tsc5", "1")
@@ -249,28 +230,6 @@ func startBed(t *testing.T) *bed {
 	return b
 }
 
-// setOnline writes the watchman's presence of a node.
-func (b *bed) setOnline(t *testing.T, node string, online bool) {
-	t.Helper()
-	data, _ := delivery.EncodePresence(delivery.Presence{Online: online})
-	if _, err := b.presence.Put(b.ctx, node, data); err != nil {
-		t.Fatal(err)
-	}
-}
-
-// setHealth writes the node-engine's have of a build module on a node, running with this health.
-func (b *bed) setHealth(t *testing.T, node, module string, health delivery.Health) {
-	t.Helper()
-	data, err := delivery.EncodeHave(delivery.Have{Phase: delivery.PhaseRunning, Health: health})
-	if err != nil {
-		t.Fatal(err)
-	}
-	key, _ := delivery.HaveKey(node, module)
-	if _, err := b.have.Put(b.ctx, key, data); err != nil {
-		t.Fatal(err)
-	}
-}
-
 // report writes a node's toolchains key of a build module and says so on the module's stream, as the module does.
 func (b *bed) report(t *testing.T, module, node, language, version, recipe string) {
 	t.Helper()
@@ -433,20 +392,8 @@ func TestAnArchiveOnlyModuleNamingNoToolchainIsBuilt(t *testing.T) {
 	}
 }
 
-// TestANodeWhoseBuildModuleIsUnhealthyIsNotUsed: the node-engine's have of mesh-build-go on n2 says failed, so only n1 builds.
-func TestANodeWhoseBuildModuleIsUnhealthyIsNotUsed(t *testing.T) {
-	b := startBed(t)
-	b.setHealth(t, "n2", "mesh-build-go", delivery.HealthFailed)
-	b.archive(t, "ca-trust", "modules/ca-trust", commit)
-	b.start(t, "n1", nil)
-	v := b.await(t, "ca-trust", isState(delivery.BuildDone))
-	if !strings.Contains(v.Step, "on n1") {
-		t.Errorf("build = %+v, want it built on n1 alone", v)
-	}
-}
-
-// TestAFailedKeyIsBuiltAgainAsANewRevisionFromANewModulesValueWithTheSameFingerprint: a build step fails on one node, so the
-// key is failed naming it; the indexer writing modules.<m> again with the same fingerprint wakes the builder, which builds
+// TestAFailedKeyIsBuiltAgainAsANewRevisionFromANewModulesValueWithTheSameFingerprint: a build step fails, so the key is
+// failed naming it; the indexer writing modules.<m> again with the same fingerprint wakes the builder, which builds
 // the key again as a new revision of the same key, now done.
 func TestAFailedKeyIsBuiltAgainAsANewRevisionFromANewModulesValueWithTheSameFingerprint(t *testing.T) { // 1607/AC6, AC7
 	b := startBed(t)
@@ -742,3 +689,32 @@ func TestABuilderWhoseBuildModulesAnsweredReferencesSaysItAndStoppedSaysNothing(
 		t.Fatalf("the stopped builder still says: %v", err)
 	}
 }
+
+// 1887/AC1, AC2 on the real bus: the builder puts the trunk fingerprint's build as asks on the build seats' delivery
+// streams and calls no node's tool; the build modules that pulled them wrote the steps, and the key is done naming the
+// references.
+func TestTheBuilderAsksTheBuildSeatsAndCallsNoNode(t *testing.T) {
+	b := startBed(t)
+	b.module(t, "netcheck", "catalogue-a67f0196-netcheck.module.json", "modules/netcheck")
+	sub, err := nats.Connect(b.srvURL, nats.UserInfo("ctl", "pw"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer sub.Close()
+	var calls atomic.Int64
+	s, err := sub.Subscribe("mesh.mod.*.call.>", func(*nats.Msg) { calls.Add(1) })
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer s.Unsubscribe()
+	b.start(t, "n1", nil)
+	v := b.await(t, "netcheck", isState(delivery.BuildDone))
+	for _, a := range v.Artifacts {
+		if a.Reference == "" {
+			t.Errorf("artifact %s names no reference", a.Name)
+		}
+	}
+	if n := calls.Load(); n != 0 {
+		t.Errorf("%d tool calls reached a build module", n)
+	}
+}
diff --git a/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/main.go b/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/main.go
index 822b325..6d597a3 100644
--- a/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/main.go
+++ b/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/main.go
@@ -26,7 +26,6 @@ import (
 	"github.com/nats-io/nats.go/jetstream"
 
 	"git.novox.be/novox/mesh-sdk/go/delivery"
-	"git.novox.be/novox/mesh-sdk/go/process"
 
 	"mesh-delivery-builder/internal/build"
 )
@@ -143,38 +142,20 @@ func run(ctx context.Context, getenv func(string) string, logOut io.Writer) erro
 	if err != nil {
 		return err
 	}
-	// Calls to the build modules go out as this module's own account, naming the machine (mesh-sdk process.CallOn); the
-	// buckets are read and written on the connection above.
-	account, err := process.ReadAccount(path)
-	if err != nil {
-		return err
-	}
-	caller, err := process.Connect(account, nats.Name(cred.Node+"."+cred.Module+".calls"), nats.RetryOnFailedConnect(true))
-	if err != nil {
-		return err
-	}
-	defer caller.Close()
-
 	bound := defaultStepBound
 	if v := strings.TrimSpace(getenv("MESH_BUILDER_STEP_BOUND")); v != "" {
 		if bound, err = time.ParseDuration(v); err != nil {
 			return fmt.Errorf("MESH_BUILDER_STEP_BOUND: %w", err)
 		}
 	}
-	capacity, err := capacityFrom(strings.TrimSpace(getenv("MESH_BUILDER_SETTINGS")), getenv("MESH_BUILDER_CAPACITY"))
-	if err != nil {
-		return fmt.Errorf("the build capacity setting: %w", err)
-	}
 	tools := &buildrun.ToolchainSet{}
-	presence := &buildrun.PresenceSet{}
-	have := &buildrun.HaveSet{}
+	// Each build module's part of a build is an ask on its build seat's stream, pulled by a build node with a free slot
+	// (novox/hq ADR 0525): the builder chooses no node, so it reads neither presence nor have and holds no capacity.
+	asks := buildrun.JetStreamAsks{JS: js}
 	b := &build.Builder{
 		Claimer:    build.Claimer{Store: kvStore{builds}, By: cred.Node + "." + cred.Module},
-		Runner:     buildrun.Runner{Caller: caller, Steps: stepsWaiter{js}, Bound: bound},
+		Asks:       buildrun.Asker{Publisher: asks, Waiter: asks, Bound: bound},
 		Toolchains: tools,
-		Presence:   presence,
-		Health:     have,
-		Places:     &buildrun.Places{Capacity: capacity},
 		Manifests:  manifestReader{manifests},
 		Logf:       logger.Printf,
 	}
@@ -219,48 +200,6 @@ func run(ctx context.Context, getenv func(string) string, logOut io.Writer) erro
 		}
 		defer cc.Stop()
 	}
-	// The watchman's presence says which nodes are asleep. Where its bucket is not there yet no node is online, so nothing
-	// builds; the builder says so and is started again with the watchman.
-	presenceErrs := make(chan error, 1)
-	switch kv, err := js.KeyValue(ctx, delivery.PresenceBucket); {
-	case errors.Is(err, jetstream.ErrBucketNotFound):
-		logger.Printf("the bucket %s does not exist yet: no node counts as online until the builder starts again", delivery.PresenceBucket)
-	case err != nil:
-		return fmt.Errorf("the bucket %s: %w", delivery.PresenceBucket, err)
-	default:
-		pw, err := settle(ctx, kv, func(e jetstream.KeyValueEntry) { presence.Put(e.Key(), e.Value(), !opOf(e)) })
-		if err != nil {
-			return err
-		}
-		go func() {
-			presenceErrs <- follow(ctx, pw, func(e jetstream.KeyValueEntry) {
-				if presence.Put(e.Key(), e.Value(), !opOf(e)) {
-					b.NodesChanged(ctx) // a node came online or went: a build that waited for one may go on
-				}
-			})
-		}()
-	}
-	// The node-engine's have says whether a node's build module runs and is healthy: a node whose build module is not is not
-	// chosen (ADR 0478 clause 3). Where its bucket is not there yet no build module counts as healthy, so nothing builds.
-	haveErrs := make(chan error, 1)
-	switch kv, err := js.KeyValue(ctx, delivery.HaveBucket); {
-	case errors.Is(err, jetstream.ErrBucketNotFound):
-		logger.Printf("the bucket %s does not exist yet: no build module counts as healthy until the builder starts again", delivery.HaveBucket)
-	case err != nil:
-		return fmt.Errorf("the bucket %s: %w", delivery.HaveBucket, err)
-	default:
-		hw, err := settle(ctx, kv, func(e jetstream.KeyValueEntry) { have.Put(e.Key(), e.Value(), !opOf(e)) })
-		if err != nil {
-			return err
-		}
-		go func() {
-			haveErrs <- follow(ctx, hw, func(e jetstream.KeyValueEntry) {
-				if have.Put(e.Key(), e.Value(), !opOf(e)) {
-					b.NodesChanged(ctx) // a build module became healthy or stopped being: a build that waited may go on
-				}
-			})
-		}()
-	}
 	each := func(e jetstream.KeyValueEntry) {
 		if opOf(e) {
 			b.Module(ctx, e.Key(), e.Value())
@@ -300,9 +239,5 @@ func run(ctx context.Context, getenv func(string) string, logOut io.Writer) erro
 		return err
 	case err := <-watch.errs:
 		return err
-	case err := <-presenceErrs:
-		return err
-	case err := <-haveErrs:
-		return err
 	}
 }
diff --git a/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/settings.go b/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/settings.go
deleted file mode 100644
index e0255f1..0000000
--- a/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/settings.go
+++ /dev/null
@@ -1,28 +0,0 @@
-package main
-
-import (
-	"encoding/json"
-	"fmt"
-	"git.novox.be/novox/mesh-sdk/go/delivery/buildrun"
-	"os"
-)
-
-// capacityFrom is the build capacity of each node (ADR 0478 clause 3): the module's setting `capacity`, `<node>=<steps at
-// once>` pairs separated by commas, laid into the settings file the controller composes (issue 1661); empty is one step at a
-// time on every node. With no settings file named, fallback is read instead, for a run outside the module's launch.
-func capacityFrom(path, fallback string) (map[string]int, error) {
-	if path == "" {
-		return buildrun.ParseCapacity(fallback)
-	}
-	raw, err := os.ReadFile(path)
-	if err != nil {
-		return nil, fmt.Errorf("the settings file: %w", err)
-	}
-	var s struct {
-		Capacity string `json:"capacity"`
-	}
-	if err := json.Unmarshal(raw, &s); err != nil {
-		return nil, fmt.Errorf("the settings file %s is not JSON: %w", path, err)
-	}
-	return buildrun.ParseCapacity(s.Capacity)
-}
diff --git a/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/settings_test.go b/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/settings_test.go
deleted file mode 100644
index 31b1acf..0000000
--- a/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/settings_test.go
+++ /dev/null
@@ -1,67 +0,0 @@
-package main
-
-import (
-	"git.novox.be/novox/mesh-sdk/go/delivery/buildrun"
-	"os"
-	"path/filepath"
-	"testing"
-)
-
-func settingsFile(t *testing.T, body string) string {
-	t.Helper()
-	p := filepath.Join(t.TempDir(), "settings.json")
-	if err := os.WriteFile(p, []byte(body), 0o600); err != nil {
-		t.Fatal(err)
-	}
-	return p
-}
-
-// 1661: the build capacity is the module's setting `capacity`, laid into the settings file: empty is one step at a time everywhere.
-func TestCapacityIsReadFromTheSettingsFile(t *testing.T) {
-	for body, want := range map[string]map[string]int{
-		`{"capacity": "shanks=3,ace=2"}`: {"shanks": 3, "ace": 2},
-		`{"capacity": ""}`:               {},
-		`{}`:                             {},
-	} {
-		got, err := capacityFrom(settingsFile(t, body), "")
-		if err != nil || len(got) != len(want) || got["shanks"] != want["shanks"] || got["ace"] != want["ace"] {
-			t.Errorf("%s: capacity %v, %v, want %v", body, got, err, want)
-		}
-	}
-	p := &buildrun.Places{Capacity: mustCapacity(t, settingsFile(t, `{"capacity": ""}`))}
-	if p.CapacityOf("shanks") != 1 || p.CapacityOf("ace") != 1 {
-		t.Errorf("an empty setting gives %d and %d, want 1 everywhere", p.CapacityOf("shanks"), p.CapacityOf("ace"))
-	}
-}
-
-func mustCapacity(t *testing.T, path string) map[string]int {
-	t.Helper()
-	c, err := capacityFrom(path, "")
-	if err != nil {
-		t.Fatal(err)
-	}
-	return c
-}
-
-func TestACapacitySettingThatIsNotOneIsRefusedNamingIt(t *testing.T) {
-	if _, err := capacityFrom(settingsFile(t, `{"capacity": "shanks=-1"}`), ""); err == nil {
-		t.Error("shanks=-1 accepted")
-	}
-	if c, err := capacityFrom(settingsFile(t, `{"capacity": "shanks=3,ace=2,g14=0,novox=0"}`), ""); err != nil || c["g14"] != 0 || len(c) != 4 {
-		t.Errorf("the starting value: %v, %v", c, err)
-	}
-	if _, err := capacityFrom(settingsFile(t, `not json`), ""); err == nil {
-		t.Error("a file that is not JSON accepted")
-	}
-	if _, err := capacityFrom(filepath.Join(t.TempDir(), "none"), ""); err == nil {
-		t.Error("a settings file that is not there accepted")
-	}
-}
-
-// With no settings file named (a run outside the module's launch, as the tests do), the capacity is the environment's.
-func TestWithNoSettingsFileTheCapacityIsTheEnvironments(t *testing.T) {
-	got, err := capacityFrom("", "ace=2")
-	if err != nil || got["ace"] != 2 {
-		t.Errorf("capacity %v, %v", got, err)
-	}
-}
diff --git a/modules/mesh-delivery-builder/files/settings.json b/modules/mesh-delivery-builder/files/settings.json
deleted file mode 100644
index 3175fe3..0000000
--- a/modules/mesh-delivery-builder/files/settings.json
+++ /dev/null
@@ -1,3 +0,0 @@
-{
-  "capacity": "shanks=3,ace=2,g14=0,novox=0"
-}
diff --git a/modules/mesh-delivery-builder/internal/build/fixtures_test.go b/modules/mesh-delivery-builder/internal/build/fixtures_test.go
index b5a6566..4ecc3e0 100644
--- a/modules/mesh-delivery-builder/internal/build/fixtures_test.go
+++ b/modules/mesh-delivery-builder/internal/build/fixtures_test.go
@@ -1,10 +1,14 @@
 package build
 
 import (
+	"context"
 	"encoding/json"
 	"os"
+	"strings"
 	"testing"
+	"time"
 
+	"git.novox.be/novox/mesh-sdk/go/buildstep"
 	"git.novox.be/novox/mesh-sdk/go/delivery"
 )
 
@@ -25,17 +29,31 @@ func captured(t *testing.T, name string) json.RawMessage {
 	return step.Result
 }
 
+// The captured image steps, run as a pulled ask runs them (buildstep.RunAsk), answer what the builder reads: the trunk's
+// build its digest and reference, a candidate's its digest and no reference (issue 1887 A4a).
 func TestCapturedImageStepsDecodeWithTheBuildersOwnTypes(t *testing.T) { // review r2, mesh-catalog 2; ADR 0487 clause 1
-	var f fetchResult
-	if err := json.Unmarshal(captured(t, "fetch.json"), &f); err != nil || f.Workspace == "" {
-		t.Errorf("fetch = %+v, %v, want a workspace (the field the builder reads)", f, err)
-	}
-	var trunk buildResult
-	if err := json.Unmarshal(captured(t, "build-trunk.json"), &trunk); err != nil || trunk.Digest == "" || trunk.Reference == "" {
-		t.Errorf("trunk build = %+v, %v, want a digest and a reference", trunk, err)
-	}
-	var cand buildResult
-	if err := json.Unmarshal(captured(t, "build-candidate.json"), &cand); err != nil || cand.Digest == "" || cand.Reference != "" {
-		t.Errorf("candidate build = %+v, %v, want a digest and no reference", cand, err)
+	for _, tc := range []struct {
+		build   string
+		publish bool
+		ref     bool
+	}{{"build-trunk.json", true, true}, {"build-candidate.json", false, false}} {
+		steps := buildstep.AskSteps{
+			Fetch: func(context.Context, map[string]any) (any, error) {
+				return json.RawMessage(captured(t, "fetch.json")), nil
+			},
+			Build: func(context.Context, map[string]any) (any, error) { return json.RawMessage(captured(t, tc.build)), nil },
+		}
+		ask := delivery.StepAsk{ID: buildstep.NewID(), Kind: delivery.AskDelivery, Language: delivery.AskImage, Asker: delivery.BuilderModule,
+			At: time.Now(), Build: &delivery.BuildJob{Module: "m", Path: "modules/m", Publish: tc.publish,
+				Fetch:     map[string]any{"repository": "novox/mesh-catalog", "commit": strings.Repeat("a", 40)},
+				Artifacts: []delivery.AskArtifact{{Artifact: "server"}}}}
+		out, err := buildstep.RunAsk(context.Background(), steps, ask)
+		if err != nil {
+			t.Fatalf("%s: %v", tc.build, err)
+		}
+		a := out.(delivery.BuildAnswer)
+		if len(a.Artifacts) != 1 || a.Artifacts[0].Digest == "" || (a.Artifacts[0].Reference != "") != tc.ref {
+			t.Errorf("%s answered %+v, want a digest and a reference only for the trunk", tc.build, a)
+		}
 	}
 }
diff --git a/modules/mesh-delivery-builder/internal/build/r4e_test.go b/modules/mesh-delivery-builder/internal/build/r4e_test.go
index d3d851c..fab0854 100644
--- a/modules/mesh-delivery-builder/internal/build/r4e_test.go
+++ b/modules/mesh-delivery-builder/internal/build/r4e_test.go
@@ -111,7 +111,7 @@ func TestADoneKeyWrittenBeforeR4eIsBuiltAgainOnceAsANewRevision(t *testing.T) {
 func TestAPinnedUpstreamIsCopiedOnceOnOneImageNodeWithNoFetchAndItsKeyNamesTheReference(t *testing.T) { // B4, ADR 0498 clause 4
 	up := catalogue.Artifact{Name: "up", Kind: "upstream", From: "nats:2.11.17-alpine@" + digest}
 	r := newRig(t, up)
-	r.b.Health = imageHave(t, "ace", "novox")
+	r.puller = "ace"
 	v := r.consider(t, "modules/m")
 	if v.State != delivery.BuildDone || len(v.Artifacts) != 1 {
 		t.Fatalf("build = %+v, want done with the copy", v)
@@ -133,7 +133,7 @@ func TestAPinnedUpstreamIsCopiedOnceOnOneImageNodeWithNoFetchAndItsKeyNamesTheRe
 
 func TestAnUpstreamBesideAnImageIsCopiedAndTheImageFetchedAndBuiltOnTheSameNode(t *testing.T) { // B4
 	r := newRig(t, imageArt, catalogue.Artifact{Name: "up", Kind: "upstream", From: "nats:2.11.17-alpine@" + digest})
-	r.b.Health = imageHave(t, "ace")
+	r.puller = "ace"
 	v := r.consider(t, "modules/m")
 	if ok, missing := v.Referenced(); !ok {
 		t.Fatalf("build = %+v, missing references %v", v, missing)
@@ -145,7 +145,7 @@ func TestAnUpstreamBesideAnImageIsCopiedAndTheImageFetchedAndBuiltOnTheSameNode(
 
 func TestACopyThatFailsNotStoredFailsTheKeyAndIsBuiltAgain(t *testing.T) { // B4, ADR 0498 clause 2
 	r := newRig(t, catalogue.Artifact{Name: "up", Kind: "upstream", From: "nats:2.11.17-alpine@" + digest})
-	r.b.Health = imageHave(t, "ace")
+	r.puller = "ace"
 	r.bm.fails["ace/build_image_copy"] = delivery.NotStored + "up: the registry answered 500"
 	v := r.consider(t, "modules/m")
 	if v.State != delivery.BuildFailed || !strings.HasPrefix(v.Error, delivery.NotStored) || delivery.FailedUntilChanged(v.Error) {
diff --git a/modules/mesh-delivery-builder/internal/build/round4_test.go b/modules/mesh-delivery-builder/internal/build/round4_test.go
index f2bcc51..e396831 100644
--- a/modules/mesh-delivery-builder/internal/build/round4_test.go
+++ b/modules/mesh-delivery-builder/internal/build/round4_test.go
@@ -3,7 +3,6 @@ package build
 import (
 	"context"
 	"git.novox.be/novox/mesh-sdk/go/delivery/buildrun"
-	"strings"
 	"testing"
 
 	"git.novox.be/novox/mesh-sdk/go/catalogue"
@@ -39,26 +38,6 @@ func TestAnArchiveOnlyModuleIsBuiltAlthoughItsFingerprintNamesNoToolchain(t *tes
 	}
 }
 
-func TestAnArchiveOnlyModuleNeedsNoAgreedToolchainButNeedsNodesThatQualify(t *testing.T) { // review round 4, 1
-	r := newRig(t, archiveA)
-	r.tools.Put(buildrun.GoBuildModule, "ace.go", tcValue(t, "go", "go1.26.0"), false) // the nodes disagree: a bundle would wait
-	r.b.Health = &buildrun.HaveSet{}                                                   // no build module is healthy anywhere
-	r.b.Module(context.Background(), "m", moduleValueWith(t, "modules/m", nil))
-	r.b.Wait()
-	if v := valueOf(t, r.st, r.key); v.State != delivery.BuildFailed || !strings.Contains(v.Error, "healthy") {
-		t.Errorf("build = %+v, want failed: no node's build module is healthy", v)
-	}
-	have := &buildrun.HaveSet{}
-	have.Put("novox.mesh-build-go", haveValue(t, delivery.PhaseRunning, delivery.HealthOK), false)
-	r.b.Health = have
-	r.b.Reconsider(context.Background())
-	r.b.Wait()
-	v := valueOf(t, r.st, r.key)
-	if v.State != delivery.BuildDone || !strings.Contains(v.Step, "on novox") {
-		t.Errorf("build = %+v, want done on novox, the one node that qualifies", v)
-	}
-}
-
 func TestABundleAndAnArchiveOfOneBuildModuleStillNeedTheAgreedToolchain(t *testing.T) { // review round 4, 1
 	p, err := PlanOf(catalogue.Manifest{Module: "m", Build: &catalogue.Build{Artifacts: []catalogue.Artifact{goBundle, archiveA}}})
 	if err != nil || !p.NeedsToolchain(buildrun.GoBuildModule) {
@@ -80,115 +59,6 @@ func TestClaimLeavesAKeyFailedForDifferingDigestsAlone(t *testing.T) { // review
 	}
 }
 
-// 4. A step never waits on a full node while another qualifying node has room.
-func TestChoosesMadeAtOnceSeeEachOthersReservationsSoNoLaneWaitsWhileANodeHasRoom(t *testing.T) { // review round 4, 4
-	p := &buildrun.Places{Capacity: map[string]int{"ace": 2, "g14": 1, "novox": 1, "shanks": 3}}
-	entries := tcs("go", "go1.27.1", "ace", "g14", "novox", "shanks")
-	total := 2 + 1 + 1 + 3
-	var waiting int
-	for i := 1; i <= 4; i++ { // four modules choose before any lane has started
-		room := 0
-		for _, n := range []string{"ace", "g14", "novox", "shanks"} {
-			room += p.CapacityOf(n) - p.Running()[n] - p.Reserved()[n]
-		}
-		nodes, _, err := buildrun.ChooseNodes("go", entries, p, nil, 2)
-		if err != nil || len(nodes) != 2 {
-			t.Fatalf("choice %d: %v, %v", i, nodes, err)
-		}
-		if room >= 2 {
-			for _, n := range nodes {
-				if p.Reserved()[n] > p.CapacityOf(n) {
-					t.Errorf("choice %d: %v put a lane on full %s while %d places were free", i, nodes, n, room)
-				}
-			}
-		} else {
-			waiting += 2 - room
-		}
-	}
-	if want := 4*2 - total; waiting != want {
-		t.Errorf("%d lanes wait, want %d: the 8 lanes less the %d places", waiting, want, total)
-	}
-	loads := p.Reserved()
-	for n, c := range loads {
-		if c > p.CapacityOf(n) && n != "shanks" && n != "ace" && n != "g14" && n != "novox" {
-			t.Errorf("unknown node %s", n)
-		}
-	}
-	if loads["shanks"] != 3 || loads["ace"] != 2 || loads["g14"]+loads["novox"] != 3 {
-		t.Errorf("reservations = %v, want shanks 3, ace 2 and the single-place nodes taking the rest", loads)
-	}
-}
-
-func TestACancelledReservationFreesTheChoiceAndAnAcquireTakesItsReservation(t *testing.T) { // review round 4, 4
-	p := &buildrun.Places{}
-	nodes, _, _ := buildrun.ChooseNodes("go", tcs("go", "go1.27.1", "ace"), p, nil, 1)
-	if len(nodes) != 1 || p.Reserved()["ace"] != 1 {
-		t.Fatalf("nodes %v, reserved %v", nodes, p.Reserved())
-	}
-	release, err := p.Acquire(context.Background(), "ace")
-	if err != nil || p.Reserved()["ace"] != 0 || p.Running()["ace"] != 1 {
-		t.Fatalf("acquire: %v, reserved %v, running %v", err, p.Reserved(), p.Running())
-	}
-	release()
-	buildrun.ChooseNodes("go", tcs("go", "go1.27.1", "ace"), p, nil, 1)
-	p.Cancel("ace")
-	if len(p.Reserved()) != 0 {
-		t.Errorf("reserved after Cancel = %v", p.Reserved())
-	}
-}
-
-// 5. A node whose build module is not healthy is not chosen.
-func TestHaveSetKnowsOnlyBuildModulesRunningAndHealthy(t *testing.T) { // review round 4, 5
-	var s buildrun.HaveSet
-	if s.Healthy("ace", buildrun.GoBuildModule) {
-		t.Error("a module with no have is healthy")
-	}
-	if !s.Put("ace.mesh-build-go", haveValue(t, delivery.PhaseRunning, delivery.HealthOK), false) || !s.Healthy("ace", buildrun.GoBuildModule) {
-		t.Error("a running, healthy module is not")
-	}
-	if s.Put("ace.mesh-build-go", haveValue(t, delivery.PhaseRunning, delivery.HealthOK), false) {
-		t.Error("the same state counted as a change")
-	}
-	if !s.Put("ace.mesh-build-go", haveValue(t, delivery.PhaseRunning, delivery.HealthFailed), false) || s.Healthy("ace", buildrun.GoBuildModule) {
-		t.Error("a module whose health failed is healthy")
-	}
-	s.Put("ace.mesh-build-go", haveValue(t, delivery.PhaseRunning, delivery.HealthOK), false)
-	if !s.Put("ace.mesh-build-go", haveValue(t, delivery.PhaseFailed, delivery.HealthOK), false) || s.Healthy("ace", buildrun.GoBuildModule) {
-		t.Error("a module whose phase failed is healthy")
-	}
-	s.Put("ace.mesh-build-go", haveValue(t, delivery.PhaseRunning, delivery.HealthOK), false)
-	if !s.Put("ace.mesh-build-go", nil, true) || s.Healthy("ace", buildrun.GoBuildModule) {
-		t.Error("a deleted have is healthy")
-	}
-	if s.Put("ace.node", []byte(`{}`), false) || s.Put("ace.mesh-build-go", []byte(`not json`), false) {
-		t.Error("a node's key or a non-have counted")
-	}
-}
-
-func TestANodeWhoseBuildModuleIsNotHealthyIsNotChosen(t *testing.T) { // review round 4, 5
-	r := newRig(t, goBundle)
-	have := &buildrun.HaveSet{}
-	have.Put("ace.mesh-build-go", haveValue(t, delivery.PhaseRunning, delivery.HealthFailed), false) // go is not the recipe's
-	have.Put("novox.mesh-build-go", haveValue(t, delivery.PhaseRunning, delivery.HealthOK), false)
-	r.b.Health = have
-	v := r.consider(t, "modules/m")
-	if v.State != delivery.BuildDone || !strings.Contains(v.Step, "on novox") {
-		t.Fatalf("build = %+v, want done on novox alone", v)
-	}
-	for _, c := range r.bm.calls {
-		if c.node == "ace" {
-			t.Errorf("a step was called on ace, whose build module is unhealthy: %+v", c)
-		}
-	}
-	have.Put("novox.mesh-build-go", haveValue(t, delivery.PhaseRunning, delivery.HealthFailed), false)
-	r.st.vals = map[string][]byte{} // a fresh key
-	r.b.Module(context.Background(), "m", moduleValue(t, "modules/m"))
-	r.b.Wait()
-	if v := valueOf(t, r.st, r.key); v.State != delivery.BuildFailed || !strings.Contains(v.Error, "healthy") {
-		t.Errorf("build = %+v, want failed: no node has a healthy build module", v)
-	}
-}
-
 // 6. A key found building is taken over, whoever holds it.
 func TestABuildLeftBuildingByAnyBuilderIsTakenOverAtStart(t *testing.T) { // review round 4, 6; 1607/AC3, ADR 0478 clauses 5, 6
 	st := newMem()
diff --git a/modules/mesh-delivery-builder/internal/build/run.go b/modules/mesh-delivery-builder/internal/build/run.go
index 3021dd0..64e3bcd 100644
--- a/modules/mesh-delivery-builder/internal/build/run.go
+++ b/modules/mesh-delivery-builder/internal/build/run.go
@@ -5,9 +5,11 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
+	"maps"
 	"sort"
 	"strings"
 	"sync"
+	"time"
 
 	"git.novox.be/novox/mesh-sdk/go/buildstep"
 	"git.novox.be/novox/mesh-sdk/go/catalogue"
@@ -20,29 +22,23 @@ type ToolchainEntries interface {
 	Entries(language string) []delivery.NodeToolchain
 }
 
-// toolPrefix is the start of each build module's tool names: <prefix>fetch and <prefix>build.
-var toolPrefix = map[string]string{buildrun.GoBuildModule: "build_go_", buildrun.NodeBuildModule: "build_node_", ImageBuildModule: "build_image_"}
-
 // Builder builds, dark, every new-form fingerprint the indexer writes (novox/hq ADR 0453 clause 4, ADR 0478): it is
 // handed each modules value as the watch of the indexer's bucket sees it, and for each module with a fingerprint and an
-// artifact to build claims the fingerprint's build key, builds it through the build modules on the nodes
-// the toolchains choose, and writes the key done or failed. It holds no timer; a build starts from a modules value or a
+// artifact to build claims the fingerprint's build key, builds it by asking the build seats (one ask per build module,
+// pulled by whichever build node has a free slot: ADR 0525), and writes the key done or failed. It holds no timer; a build starts from a modules value or a
 // change of the toolchains.
 type Builder struct {
-	Claimer    Claimer
-	Runner     buildrun.Runner
-	Toolchains ToolchainEntries
-	// Presence says which nodes are online (the watchman's); a node that is not is not chosen.
-	Presence  interface{ Online(node string) bool }
-	Manifests Manifests
-	// Health says whether a node's build module is running and healthy (the node-engine's have); a node whose build module
-	// is not is not chosen. Nil means every node's is.
-	Health interface {
-		Healthy(node, module string) bool
+	Claimer Claimer
+	// Asks puts each build module's part of a build as one ask on its build seat's stream and waits for its step (novox/hq
+	// ADR 0525 §1, §3, §6; issue 1887 A4): the builder chooses no node, whichever build node pulls the ask builds it.
+	Asks interface {
+		Put(ctx context.Context, a delivery.StepAsk) error
+		Wait(ctx context.Context, a delivery.StepAsk) (delivery.Step, error)
 	}
-	// buildrun.Places holds a step back while its node is at its build capacity; a Builder with none runs one step at a time on each node.
-	Places *buildrun.Places
-	// Limit is how many builds run at once; four when 0.
+	Toolchains ToolchainEntries
+	Manifests  Manifests
+	// Limit is how many builds the builder has asked at once; their asks wait in the build seats' streams, which are the
+	// backlog (ADR 0525 §9), not here. 256 when 0.
 	Limit int
 	Logf  func(format string, args ...any)
 	// Answered is told the build module whose step answered a reference (issue 1886): what the builder says it writes
@@ -75,15 +71,12 @@ func (b *Builder) init() {
 	b.once.Do(func() {
 		limit := b.Limit
 		if limit <= 0 {
-			limit = 4
+			limit = 256
 		}
 		b.sem = make(chan struct{}, limit)
 		b.cands, b.via, b.trunkFP = map[string]delivery.Candidate{}, map[string]via{}, map[string]bool{}
 		b.known, b.inflight, b.again, b.plans, b.tried = map[string]delivery.Module{}, map[string]bool{}, map[string]delivery.Module{}, map[string]planned{}, map[string]bool{}
 		b.published = map[string]bool{}
-		if b.Places == nil {
-			b.Places = &buildrun.Places{}
-		}
 	})
 }
 
@@ -116,8 +109,7 @@ func (b *Builder) Module(ctx context.Context, key string, value []byte) {
 	b.consider(ctx, key, m)
 }
 
-// NodesChanged is Reconsider after a change of the nodes: one came online or went, a build module became healthy or
-// stopped being, or a toolchain moved, so a build that waited for a node may go on.
+// NodesChanged is Reconsider after a toolchain moved, so a build that waited for the nodes to agree on one may go on.
 func (b *Builder) NodesChanged(ctx context.Context) { b.Reconsider(ctx) }
 
 // Sweep reads, at start, every key of the bucket: it keeps the package versions done keys name as published (a key
@@ -314,7 +306,7 @@ func (b *Builder) try(ctx context.Context, module string, m delivery.Module) {
 	first := !b.tried[key]
 	b.tried[key] = true
 	b.mu.Unlock()
-	cl, err := b.Claimer.Claim(ctx, module, m.FP2, m.Manifest, ClaimOptions{TakeOver: first, ImageBuilder: b.imageBuilderRuns, Trunk: trunk, Published: b.isPublished})
+	cl, err := b.Claimer.Claim(ctx, module, m.FP2, m.Manifest, ClaimOptions{TakeOver: first, ImageBuilder: imageSeat, Trunk: trunk, Published: b.isPublished})
 	if err != nil {
 		b.logf("%s: %v", module, err)
 		return
@@ -330,7 +322,7 @@ func (b *Builder) try(ctx context.Context, module string, m delivery.Module) {
 	if cl.Build.State == delivery.BuildDone {
 		prior, only = &cl.Build, map[string]bool{}
 		if trunk {
-			for _, bm := range publishable(cl.Build, b.imageBuilderRuns) {
+			for _, bm := range publishable(cl.Build, imageSeat) {
 				only[bm] = true
 				publishing = true
 			}
@@ -342,7 +334,7 @@ func (b *Builder) try(ctx context.Context, module string, m delivery.Module) {
 		// any other, so the controller has a done key to register it from (issue 1613, ADR 0478 clause 1, ADR 0501 clause 1).
 		result = delivery.BuilderBuild{State: delivery.BuildDone, Step: "nothing to build: the manifest names no artifact"}
 	} else {
-		result = b.build(ctx, module, m, plan, planErr, prior, only)
+		result = b.build(ctx, module, m, plan, planErr, prior, only, b.notes(cl))
 	}
 	if ctx.Err() != nil {
 		return
@@ -399,14 +391,15 @@ func failed(format string, args ...any) delivery.BuilderBuild {
 
 // lane is the build of a plan's tasks of one build module on one node.
 type lane struct {
-	module, node string
+	module, node string // node is the one that pulled the lane's ask
 	tasks        []Task
+	toolchain    *delivery.ToolchainUsed
 	digests      map[string]string // artifact -> digest
 	references   map[string]string // artifact -> the reference an image was pushed to (a trunk build only)
 	err          error
 }
 
-func (b *Builder) build(ctx context.Context, module string, m delivery.Module, plan Plan, planErr error, prior *delivery.BuilderBuild, only map[string]bool) delivery.BuilderBuild {
+func (b *Builder) build(ctx context.Context, module string, m delivery.Module, plan Plan, planErr error, prior *delivery.BuilderBuild, only map[string]bool, asked *askNotes) delivery.BuilderBuild {
 	switch {
 	case planErr != nil:
 		return failed("%s", planErr)
@@ -417,76 +410,39 @@ func (b *Builder) build(ctx context.Context, module string, m delivery.Module, p
 	repository := delivery.RepositoryName(m.Repository)
 	var lanes []*lane
 	used := map[string]delivery.ToolchainUsed{}
-	var steps []string
-	// Every node chosen holds a reservation until its lane takes the place; a build that ends before its lanes start gives them up.
-	giveUp := func(nodes ...string) {
-		for _, n := range nodes {
-			b.Places.Cancel(n)
-		}
-	}
-	giveUpLanes := func() {
-		for _, l := range lanes {
-			b.Places.Cancel(l.node)
-		}
-	}
 	var kept []string // build modules whose artifacts stay as the prior done key has them
 	for _, bm := range plan.Modules() {
 		if prior != nil && len(only) > 0 && !only[bm] {
 			kept = append(kept, bm)
 			continue
 		}
-		language := buildrun.LanguageOf[bm]
-		entries := b.Toolchains.Entries(language)
-		qualifies := func(node string) bool { return b.qualifies(node, bm) }
-		var nodes []string
-		if bm == ImageBuildModule {
-			// An image is built on one node, chosen from the nodes whose image build module runs healthy (ADR 0487 clause 8):
-			// the module has no toolchain language, so no toolchain entry names its nodes, and a second build would only
-			// push the image again.
-			ns, err := buildrun.ChooseAnyNodes("image", b.imageEntries(), b.Places, qualifies, 1)
-			if err != nil {
-				giveUpLanes()
-				return failed("%s no node has %s, so the image cannot be built: the provision rootless-image-build is held by the module buildah; assign buildah and %s to a node (%v)", NoImageBuilderPrefix, ImageBuildModule, ImageBuildModule, err)
-			}
-			nodes = ns
-		} else if plan.NeedsToolchain(bm) {
-			ns, tc, err := buildrun.ChooseNodes(language, entries, b.Places, qualifies, 1)
-			if err != nil {
-				giveUpLanes()
-				return failed("%s", err)
+		var toolchain *delivery.ToolchainUsed
+		if bm != ImageBuildModule && plan.NeedsToolchain(bm) {
+			// The ask names the toolchain the fingerprint was computed with; a node building with another refuses it.
+			language := buildrun.LanguageOf[bm]
+			tc, none := delivery.AgreedToolchain(b.Toolchains.Entries(language))
+			if none != "" {
+				return failed("the %s toolchain is not agreed: %s", language, none)
 			}
 			if want := m.Toolchains[language]; want.Version != tc.Version || want.Recipe != tc.Recipe {
-				giveUp(ns...)
-				giveUpLanes()
 				return delivery.BuilderBuild{} // the agreed toolchain moved since try looked: nothing is written
 			}
-			used[language] = delivery.ToolchainUsed{Version: tc.Version, Recipe: tc.Recipe}
-			nodes = ns
-		} else {
-			// An archive is packed with no toolchain (the fingerprint names none): any node of the build module that qualifies.
-			ns, err := buildrun.ChooseAnyNodes(language, entries, b.Places, qualifies, 1)
-			if err != nil {
-				giveUpLanes()
-				return failed("%s", err)
-			}
-			nodes = ns
+			u := delivery.ToolchainUsed{Version: tc.Version, Recipe: tc.Recipe}
+			used[language], toolchain = u, &u
 		}
-		// One node builds each fingerprint (ADR 0478 clause 4, from R4e).
-		steps = append(steps, fmt.Sprintf("%s on %s", bm, nodes[0]))
 		var tasks []Task
 		for _, t := range plan.Tasks {
 			if t.Module == bm {
 				tasks = append(tasks, t)
 			}
 		}
-		for _, n := range nodes {
-			lanes = append(lanes, &lane{module: bm, node: n, tasks: tasks, digests: map[string]string{}, references: map[string]string{}})
-		}
+		// One ask builds each fingerprint's part of a build module, on whichever node pulls it (ADR 0525 §3).
+		lanes = append(lanes, &lane{module: bm, tasks: tasks, toolchain: toolchain, digests: map[string]string{}, references: map[string]string{}})
 	}
 	var wg sync.WaitGroup
 	for _, l := range lanes {
 		wg.Add(1)
-		go func() { defer wg.Done(); b.runLane(ctx, l, repository, m, module) }()
+		go func() { defer wg.Done(); b.runLane(ctx, l, repository, m, module, asked) }()
 	}
 	wg.Wait()
 	var errs []string
@@ -548,6 +504,10 @@ func (b *Builder) build(ctx context.Context, module string, m delivery.Module, p
 		}
 		artifacts = append(artifacts, built)
 	}
+	var steps []string
+	for _, l := range lanes {
+		steps = append(steps, fmt.Sprintf("%s on %s", l.module, l.node))
+	}
 	for _, bm := range kept {
 		steps = append(steps, bm+" kept")
 		for lang, u := range prior.Toolchains {
@@ -617,73 +577,56 @@ func keyError(errs []string) string {
 	return strings.Join(errs, "; ")
 }
 
-func (b *Builder) online(node string) bool { return b.Presence == nil || b.Presence.Online(node) }
+// imageSeat says an image build is asked of the image build seat, which takes it when a node pulls it: a key failed for
+// want of an image builder before R4g is taken again (ADR 0525 §1).
+func imageSeat() bool { return true }
 
-// qualifies is whether the node can build with the build module now: it is online and the build module on it is healthy.
-func (b *Builder) qualifies(node, bm string) bool {
-	return b.Places.CapacityOf(node) > 0 && b.online(node) && (b.Health == nil || b.Health.Healthy(node, bm))
+// askLanguage is the build seat language of each build module (delivery.AskSubject).
+var askLanguage = map[string]string{buildrun.GoBuildModule: delivery.AskGo, buildrun.NodeBuildModule: delivery.AskNode, ImageBuildModule: delivery.AskImage}
+
+// askNotes writes a claimed key's asks into it, building, before each is put (ADR 0525 §1; issue 1887 A4b), and holds
+// the asks a key taken over at start already names, so they are waited for and never put again.
+type askNotes struct {
+	mu      sync.Mutex
+	b       *Builder
+	cl      *Claim
+	resumed map[string]string
 }
 
-// imageEntries are the nodes an image may be built on, as toolchain entries for the chooser: every node the builder has a
-// capacity for or a build module toolchain from. Whether the image build module runs there is qualifies', from the have.
-func (b *Builder) imageEntries() []delivery.NodeToolchain {
-	seen := map[string]bool{}
-	var entries []delivery.NodeToolchain
-	add := func(n string) {
-		if !seen[n] {
-			seen[n] = true
-			entries = append(entries, delivery.NodeToolchain{Node: n})
-		}
+func (b *Builder) notes(cl *Claim) *askNotes {
+	n := &askNotes{b: b, cl: cl}
+	if cl.Build.State == delivery.BuildBuilding && len(cl.Build.Asks) > 0 {
+		n.resumed = maps.Clone(cl.Build.Asks)
 	}
-	for n := range b.Places.Capacity {
-		add(n)
+	return n
+}
+
+// resume is the id of the ask a taken-over key names for language, or "".
+func (n *askNotes) resume(language string) string {
+	n.mu.Lock()
+	defer n.mu.Unlock()
+	return n.resumed[language]
+}
+
+// note writes the ask's id into the key, building, by compare-and-set at the claim's revision.
+func (n *askNotes) note(ctx context.Context, language, id, step string) error {
+	n.mu.Lock()
+	defer n.mu.Unlock()
+	v := n.cl.Build
+	v.State, v.By, v.Step, v.Error, v.Artifacts = delivery.BuildBuilding, n.b.Claimer.By, step, "", nil
+	v.Asks = maps.Clone(v.Asks)
+	if v.Asks == nil {
+		v.Asks = map[string]string{}
 	}
-	for _, language := range []string{"go", "typescript"} {
-		for _, e := range b.Toolchains.Entries(language) {
-			add(e.Node)
-		}
-	}
-	sort.Slice(entries, func(i, j int) bool { return entries[i].Node < entries[j].Node })
-	return entries
+	v.Asks[language] = id
+	return n.b.Claimer.Finish(ctx, n.cl, v)
 }
 
-// imageBuilderRuns is whether a node can build an image now.
-func (b *Builder) imageBuilderRuns() bool {
-	for _, e := range b.imageEntries() {
-		if b.qualifies(e.Node, ImageBuildModule) {
-			return true
-		}
-	}
-	return false
-}
-
-// step runs one step of a build module; the lane that runs it holds its node's place.
-func (b *Builder) step(ctx context.Context, bm, node, tool string, args map[string]any) (json.RawMessage, error) {
-	return b.Runner.Run(ctx, bm, node, toolPrefix[bm]+tool, args)
-}
-
-// fetchResult and buildResult are the results of a build module's fetch and build steps as the builder reads them.
-type fetchResult struct {
-	Workspace string   `json:"workspace"`
-	Merge     string   `json:"merge"`
-	Conflicts []string `json:"conflicts"`
-}
-
-type buildResult struct {
-	Digest    string `json:"digest"`
-	Reference string `json:"reference"`
-}
-
-// runLane takes a place on the node, fetches the commit there and builds each of the lane's artifacts, one step at a time.
-// An upstream artifact is copied by its pinned reference with no fetch (ADR 0498 clause 4); a lane of copies alone fetches
-// nothing.
-func (b *Builder) runLane(ctx context.Context, l *lane, repository string, m delivery.Module, module string) {
-	release, err := b.Places.Acquire(ctx, l.node)
-	if err != nil {
-		l.err = err
-		return
-	}
-	defer release()
+// runLane puts the lane's part of the build as one ask on its build seat's stream (the delivery stream for a trunk key, the
+// check stream for a candidate's) and reads what the node that pulled it built (ADR 0525 §1, §3, §6). An upstream artifact
+// is copied by its pinned reference with no fetch (ADR 0498 clause 4); a lane of copies alone fetches nothing. A lane of a
+// key taken over at start waits for the ask the key names and puts none.
+func (b *Builder) runLane(ctx context.Context, l *lane, repository string, m delivery.Module, module string, asked *askNotes) {
 	req := buildstep.FetchRequest{Repository: repository, Commit: m.Commit}
 	if key, err := delivery.BuilderBuildKey(module, m.FP2); err == nil {
 		b.mu.Lock()
@@ -702,57 +645,69 @@ func (b *Builder) runLane(ctx context.Context, l *lane, repository string, m del
 		}
 		sort.Strings(req.Paths)
 	}
-	fetchArgs := req.Args()
 	candidate := req.Base != ""
-	var fetched fetchResult
+	language := askLanguage[l.module]
+	kind := delivery.AskDelivery
+	if candidate {
+		kind = delivery.AskCheck
+	}
+	job := &delivery.BuildJob{Module: module, Path: m.Path, FP: m.FP2, Toolchain: l.toolchain,
+		// Only a trunk key's build pushes an image or publishes a package; a candidate's never does (ADR 0487 clause 12,
+		// ADR 0498 clauses 5 and 6). A bundle or an archive is pushed either way (clause 3).
+		Publish: !candidate}
+	for _, t := range l.tasks {
+		a := delivery.AskArtifact{Artifact: t.Artifact}
+		if t.Kind == catalogue.ArtifactUpstream {
+			a.From = t.From // the copy runs no code of a change: the module's name, the artifact and its pin
+		}
+		job.Artifacts = append(job.Artifacts, a)
+	}
 	if needsFetch(l.tasks) {
-		raw, err := b.step(ctx, l.module, l.node, "fetch", fetchArgs)
-		if err != nil {
+		job.Fetch = req.Args()
+	}
+	ask := delivery.StepAsk{ID: buildstep.NewID(), Kind: kind, Language: language, Asker: delivery.BuilderModule, At: time.Now(), Build: job}
+	if id := asked.resume(language); id != "" {
+		ask.ID = id // put before this builder started again: the stream holds it, or a node already ran it
+	} else {
+		if err := asked.note(ctx, language, ask.ID, "asked "+l.module); err != nil {
+			l.err = fmt.Errorf("the ask of %s could not be written to the key: %w", l.module, err)
+			return
+		}
+		if err := b.Asks.Put(ctx, ask); err != nil {
 			l.err = err
 			return
 		}
-		if err := json.Unmarshal(raw, &fetched); err != nil || fetched.Workspace == "" {
-			l.err = fmt.Errorf("the fetch on %s answered no workspace: %s", l.node, raw)
-			return
-		}
-		// A candidate is built from its head merged onto the trunk. A head that does not merge ends the fetch passed with the tree at
-		// the trunk, and building that would store the trunk's build under the candidate's fingerprint.
-		if candidate {
-			if len(fetched.Conflicts) > 0 {
-				l.err = fmt.Errorf("the head does not merge into the trunk on %s: files in conflict: %s", l.node, strings.Join(fetched.Conflicts, ", "))
-				return
-			}
-			if fetched.Merge == "" {
-				l.err = fmt.Errorf("the fetch with a base on %s answered no merge: %s", l.node, raw)
-				return
-			}
-		}
+	}
+	step, err := b.Asks.Wait(ctx, ask)
+	if err != nil {
+		l.err = fmt.Errorf("%s: %w", l.module, err)
+		return
+	}
+	l.node = step.Node
+	if step.State != delivery.StepPassed {
+		l.err = fmt.Errorf("%s on %s: the ask %s %s: %s", l.module, step.Node, ask.ID, step.State, step.Reason)
+		return
+	}
+	var answer delivery.BuildAnswer
+	if err := json.Unmarshal(step.Result, &answer); err != nil {
+		l.err = fmt.Errorf("the ask of %s on %s answered what is not a build: %s", l.module, step.Node, step.Result)
+		return
+	}
+	built := map[string]delivery.AskBuilt{}
+	for _, a := range answer.Artifacts {
+		built[a.Artifact] = a
 	}
 	for _, t := range l.tasks {
-		tool, args := "build", map[string]any{"workspace": fetched.Workspace, "module": m.Path, "artifact": t.Artifact}
-		if t.Kind == catalogue.ArtifactUpstream {
-			// The copy runs no code of a change: the module's name (the reference's path), the artifact and its pin.
-			tool, args = "copy", map[string]any{"module": module, "artifact": t.Artifact, "from": t.From}
-		} else if !candidate {
-			// Only a trunk key's build pushes an image or publishes a package; a candidate's never does (ADR 0487 clause 12,
-			// ADR 0498 clauses 5 and 6). A bundle or an archive is pushed either way (clause 3).
-			args["publish"] = true
-		}
-		raw, err := b.step(ctx, l.module, l.node, tool, args)
-		if err != nil {
-			l.err = err
+		a, ok := built[t.Artifact]
+		if !ok || a.Digest == "" {
+			l.err = fmt.Errorf("the build of %s of %s on %s answered no digest: %s", t.Artifact, module, step.Node, step.Result)
 			return
 		}
-		var built buildResult
-		if err := json.Unmarshal(raw, &built); err != nil || built.Digest == "" {
-			l.err = fmt.Errorf("the %s of %s of %s on %s answered no digest: %s", tool, t.Artifact, module, l.node, raw)
-			return
+		l.digests[t.Artifact] = a.Digest
+		if a.Reference != "" && (stored(t.Kind) || !candidate) {
+			l.references[t.Artifact] = a.Reference
 		}
-		l.digests[t.Artifact] = built.Digest
-		if built.Reference != "" && (stored(t.Kind) || !candidate) {
-			l.references[t.Artifact] = built.Reference
-		}
-		if built.Reference != "" && b.Answered != nil {
+		if a.Reference != "" && b.Answered != nil {
 			b.Answered(l.module)
 		}
 	}
diff --git a/modules/mesh-delivery-builder/internal/build/run_test.go b/modules/mesh-delivery-builder/internal/build/run_test.go
index 4a8524c..ba94b0e 100644
--- a/modules/mesh-delivery-builder/internal/build/run_test.go
+++ b/modules/mesh-delivery-builder/internal/build/run_test.go
@@ -10,6 +10,7 @@ import (
 	"testing"
 	"time"
 
+	"git.novox.be/novox/mesh-sdk/go/buildstep"
 	"git.novox.be/novox/mesh-sdk/go/catalogue"
 	"git.novox.be/novox/mesh-sdk/go/delivery"
 )
@@ -124,22 +125,56 @@ type rig struct {
 	st    *memStore
 	bm    *buildModules
 	tools *buildrun.ToolchainSet
-	pres  *buildrun.PresenceSet
 	mf    *fakeManifests
 	key   string
+	// asks are the build seats' streams; puller is the node that pulls every ask ("ace" when empty).
+	asks   *buildrun.FakeAsks
+	puller string
+}
+
+// toolPrefix is the start of each build module's tool names, as the fake build modules answer them.
+var toolPrefix = map[string]string{buildrun.GoBuildModule: "build_go_", buildrun.NodeBuildModule: "build_node_", ImageBuildModule: "build_image_"}
+
+// answer runs an ask as the build module that pulls it does (buildstep.RunAsk), with the fake build modules' tools on the
+// rig's pulling node, and answers the step that node writes.
+func (r *rig) answer(a delivery.StepAsk) delivery.Step {
+	node := r.puller
+	if node == "" {
+		node = "ace"
+	}
+	module, _ := delivery.BuildModuleOf(a.Language)
+	runner := buildrun.Runner{Caller: r.bm, Steps: r.bm.steps, Bound: time.Second}
+	tool := func(name string) buildstep.StepFunc {
+		return func(ctx context.Context, args map[string]any) (any, error) {
+			raw, err := runner.Run(ctx, module, node, toolPrefix[module]+name, args)
+			if err != nil {
+				return nil, err
+			}
+			return raw, nil
+		}
+	}
+	steps := buildstep.AskSteps{Fetch: tool("fetch"), Build: tool("build"), Copy: tool("copy")}
+	out, err := buildstep.RunAsk(context.Background(), steps, a)
+	step := delivery.Step{ID: a.ID, Tool: a.Kind + " ask", Node: node, State: delivery.StepPassed}
+	if err != nil {
+		step.State, step.Reason = delivery.StepFailed, err.Error()
+		return step
+	}
+	step.Result, _ = json.Marshal(out)
+	return step
 }
 
 func newRig(t *testing.T, artifacts ...catalogue.Artifact) *rig {
 	t.Helper()
-	r := &rig{st: newMem(), bm: newBuildModules(), tools: &buildrun.ToolchainSet{}, pres: &buildrun.PresenceSet{}, mf: &fakeManifests{byDigest: map[string]catalogue.Manifest{mdigest('a'): {Module: "m", Build: &catalogue.Build{Artifacts: artifacts}}}}}
+	r := &rig{st: newMem(), bm: newBuildModules(), tools: &buildrun.ToolchainSet{}, mf: &fakeManifests{byDigest: map[string]catalogue.Manifest{mdigest('a'): {Module: "m", Build: &catalogue.Build{Artifacts: artifacts}}}}}
 	for _, n := range []string{"ace", "novox"} {
 		r.tools.Put(buildrun.GoBuildModule, n+".go", tcValue(t, "go", "go1.27.1"), false)
 		r.tools.Put(buildrun.NodeBuildModule, n+".typescript", tcValue(t, "typescript", "tsc5"), false)
-		r.pres.Put(n, presenceValue(t, true), false)
 	}
+	r.asks = &buildrun.FakeAsks{Answer: r.answer}
 	r.b = &Builder{
-		Claimer: Claimer{Store: r.st, By: "novox.builder"}, Runner: buildrun.Runner{Caller: r.bm, Steps: r.bm.steps, Bound: time.Second},
-		Toolchains: r.tools, Presence: r.pres, Manifests: r.mf, Logf: t.Logf,
+		Claimer: Claimer{Store: r.st, By: "novox.builder"}, Asks: buildrun.Asker{Publisher: r.asks, Waiter: r.asks, Bound: 2 * time.Second},
+		Toolchains: r.tools, Manifests: r.mf, Logf: t.Logf,
 	}
 	var err error
 	if r.key, err = delivery.BuilderBuildKey("m", fp1); err != nil {
@@ -220,15 +255,53 @@ func TestABundleAndAnArchiveAreBuiltOnOneNodeAndDone(t *testing.T) { // 1607/AC7
 	}
 }
 
-func TestOneQualifyingNodeBuildsOnce(t *testing.T) { // 1607/AC4, ADR 0478 clause 4
+// 1887/AC1, AC2: a trunk fingerprint with no key is one ask on the Go seat's delivery stream, named in the building key
+// before it is put, and the builder calls no node; the step a node wrote for it makes the key done naming its reference.
+func TestATrunkFingerprintIsOneAskOnTheDeliveryStream(t *testing.T) {
 	r := newRig(t, goBundle)
-	r.tools.Put(buildrun.GoBuildModule, "ace.go", nil, true)
-	v := r.consider(t, "modules/m")
-	if v.State != delivery.BuildDone || !strings.Contains(v.Step, "on novox") {
-		t.Errorf("build = %+v, want done with its step saying novox", v)
+	r.asks.Answer = nil // no node has pulled it yet
+	r.b.Module(context.Background(), "m", moduleValue(t, "modules/m"))
+	var asks []delivery.StepAsk
+	for deadline := time.Now().Add(2 * time.Second); len(asks) == 0; time.Sleep(time.Millisecond) {
+		if time.Now().After(deadline) {
+			t.Fatal("no ask was put")
+		}
+		asks = r.asks.Asks()
 	}
-	if n := len(r.bm.callsOf("build_go_build")); n != 1 {
-		t.Errorf("%d builds, want one", n)
+	a := asks[0]
+	if len(asks) != 1 || a.Kind != delivery.AskDelivery || a.Language != delivery.AskGo || a.Build == nil || a.Build.FP != fp1 {
+		t.Fatalf("asks = %+v, want one Go delivery ask of the fingerprint", asks)
+	}
+	if v := valueOf(t, r.st, r.key); v.State != delivery.BuildBuilding || v.Asks[delivery.AskGo] != a.ID {
+		t.Fatalf("the key = %+v, want building naming the ask %s", v, a.ID)
+	}
+	if n := len(r.bm.callsOf("build_go_build")) + len(r.bm.callsOf("build_go_fetch")); n != 0 {
+		t.Fatalf("the builder called a node %d times", n)
+	}
+	r.asks.End(r.answer(a)) // a node pulled it and ran it
+	r.b.Wait()
+	if v := valueOf(t, r.st, r.key); v.State != delivery.BuildDone || !strings.Contains(v.Step, "on ace") || v.Artifacts[0].Reference == "" || len(v.Asks) != 0 {
+		t.Fatalf("the key = %+v, want done on ace naming the reference", v)
+	}
+}
+
+// 1887/AC3: a builder that starts again while its ask waits puts no second ask: it waits for the step of the ask the
+// building key names.
+func TestARestartedBuilderWaitsForTheAskTheKeyNames(t *testing.T) {
+	r := newRig(t, goBundle)
+	const id = "mvl0frv18d1957"
+	data, _ := delivery.EncodeBuilderBuild(delivery.BuilderBuild{State: delivery.BuildBuilding, By: "novox.builder", Manifest: manifestD,
+		Step: "asked mesh-build-go", Asks: map[string]string{delivery.AskGo: id}})
+	r.st.vals[r.key] = data
+	r.asks.Answer = nil
+	r.asks.End(delivery.Step{ID: id, Node: "shanks", State: delivery.StepPassed,
+		Result: []byte(`{"artifacts":[{"artifact":"tool","digest":"` + digest + `","reference":"artifact-store://m/tool/blobs/` + digest + `"}]}`)})
+	v := r.consider(t, "modules/m")
+	if n := len(r.asks.Asks()); n != 0 {
+		t.Fatalf("%d asks put again", n)
+	}
+	if v.State != delivery.BuildDone || !strings.Contains(v.Step, "on shanks") {
+		t.Fatalf("the key = %+v, want done from the ask's step on shanks", v)
 	}
 }
 
@@ -247,20 +320,9 @@ func TestAFailingStepFailsTheBuildWithItsReasonAndNodeAndIsTriedAgainAsANewRevis
 	}
 }
 
-// imageHave marks mesh-build-image running and healthy on these nodes.
-func imageHave(t *testing.T, nodes ...string) *buildrun.HaveSet {
-	t.Helper()
-	have := &buildrun.HaveSet{}
-	for _, n := range nodes {
-		have.Put(n+".mesh-build-go", haveValue(t, delivery.PhaseRunning, delivery.HealthOK), false)
-		have.Put(n+"."+ImageBuildModule, haveValue(t, delivery.PhaseRunning, delivery.HealthOK), false)
-	}
-	return have
-}
-
 func TestAnImageGoesToOneNodeAndGetsOneDoneKeyWithItsReference(t *testing.T) { // 1705a, ADR 0487 clause 5
 	r := newRig(t, imageArt)
-	r.b.Health = imageHave(t, "ace", "novox") // two nodes qualify; an image still builds on one
+	r.puller = "ace" // two nodes qualify; an image still builds on one
 	v := r.consider(t, "modules/m")
 	if v.State != delivery.BuildDone || len(v.Artifacts) != 1 || v.Artifacts[0].Kind != "image" || v.Artifacts[0].Digest != digest {
 		t.Fatalf("build = %+v, want done with one image artifact and its digest", v)
@@ -278,19 +340,9 @@ func TestAnImageGoesToOneNodeAndGetsOneDoneKeyWithItsReference(t *testing.T) { /
 	}
 }
 
-func TestAnImageIsBuiltOnlyWhereMeshBuildImageIsHealthy(t *testing.T) { // 1705a
-	r := newRig(t, imageArt)
-	r.b.Health = imageHave(t, "novox")
-	r.consider(t, "modules/m")
-	c := r.bm.callsOf("build_image_build")
-	if len(c) != 1 || c[0].node != "novox" {
-		t.Errorf("calls = %+v, want one on novox", c)
-	}
-}
-
 func TestABundleAndAnImageOfOneModuleBuildOnOneNodeEach(t *testing.T) { // 1705a
 	r := newRig(t, goBundle, imageArt)
-	r.b.Health = imageHave(t, "ace", "novox")
+	r.puller = "ace"
 	v := r.consider(t, "modules/m")
 	if v.State != delivery.BuildDone || len(v.Artifacts) != 2 {
 		t.Fatalf("build = %+v", v)
@@ -303,33 +355,9 @@ func TestABundleAndAnImageOfOneModuleBuildOnOneNodeEach(t *testing.T) { // 1705a
 	}
 }
 
-func TestWithNoImageNodeTheKeyFailsNamingTheProvisionAndIsNotRetakenUntilANodeReportsTheModule(t *testing.T) { // 1705b, lead's decision
-	r := newRig(t, imageArt)
-	r.b.Health = imageHave(t) // mesh-build-image runs nowhere
-	v := r.consider(t, "modules/m")
-	if v.State != delivery.BuildFailed || !strings.HasPrefix(v.Error, NoImageBuilderPrefix) || !strings.Contains(v.Error, "rootless-image-build") || !strings.Contains(v.Error, "buildah") || !strings.Contains(v.Error, ImageBuildModule) {
-		t.Fatalf("build = %+v, want failed naming rootless-image-build, buildah and mesh-build-image", v)
-	}
-	if len(r.bm.calls) != 0 {
-		t.Errorf("%d calls, want none", len(r.bm.calls))
-	}
-	writes := r.st.writes
-	r.consider(t, "modules/m")
-	r.consider(t, "modules/m")
-	if r.st.writes != writes {
-		t.Errorf("the failed key was written again (%d writes, was %d)", r.st.writes, writes)
-	}
-	// A node reports the module: the key is taken again.
-	r.b.Health = imageHave(t, "ace")
-	v = r.consider(t, "modules/m")
-	if v.State != delivery.BuildDone {
-		t.Errorf("build = %+v, want done once a node reports mesh-build-image", v)
-	}
-}
-
 func TestACandidatesImageCallCarriesNoPublishAndItsKeyNoReference(t *testing.T) { // 1705b, lead's decision
 	r := newRig(t, imageArt)
-	r.b.Health = imageHave(t, "ace")
+	r.puller = "ace"
 	trunkModule(t, r)
 	r.b.Candidate(context.Background(), "feat%2Fx", candidateValue(t, "feat/x", 7, headX))
 	r.b.Wait()
@@ -348,7 +376,7 @@ func TestACandidatesImageCallCarriesNoPublishAndItsKeyNoReference(t *testing.T)
 
 func TestATrunkImageCallCarriesPublish(t *testing.T) { // 1705b
 	r := newRig(t, imageArt)
-	r.b.Health = imageHave(t, "ace")
+	r.puller = "ace"
 	r.consider(t, "modules/m")
 	calls := r.bm.callsOf("build_image_build")
 	if len(calls) != 1 || calls[0].body.(map[string]any)["publish"] != true {
@@ -439,7 +467,7 @@ func TestAKeyTheBuilderLeftBuildingIsBuiltAtStartAndDoneKeysAreNotBuiltTwice(t *
 // whose compare-and-set comes first, and the other's write is refused, never overwriting it.
 func TestTwoInstancesStartingTogetherEndWithOneDoneKey(t *testing.T) { // 1607/AC7, review round 4
 	r := newRig(t, goBundle)
-	other := &Builder{Claimer: Claimer{Store: r.st, By: "ace.builder"}, Runner: r.b.Runner, Toolchains: r.tools, Presence: r.pres, Manifests: r.mf, Logf: t.Logf}
+	other := &Builder{Claimer: Claimer{Store: r.st, By: "ace.builder"}, Asks: r.b.Asks, Toolchains: r.tools, Manifests: r.mf, Logf: t.Logf}
 	value := moduleValue(t, "modules/m")
 	var wg sync.WaitGroup
 	for _, b := range []*Builder{r.b, other} {
@@ -522,36 +550,9 @@ func TestARootModulesPathIsDotAndIsGivenToTheBuildTools(t *testing.T) { // 1615/
 	}
 }
 
-func TestANodeThatIsNotOnlineIsNotChosenAndComingBackWakesTheBuild(t *testing.T) { // 1607 review 3
-	r := newRig(t, goBundle)
-	r.tools.Put(buildrun.GoBuildModule, "g14.go", tcValue(t, "go", "go1.27.1"), false) // a laptop that reports its toolchain and sleeps
-	v := r.consider(t, "modules/m")
-	if v.State != delivery.BuildDone {
-		t.Fatalf("build = %+v", v)
-	}
-	for _, c := range r.bm.calls {
-		if c.node == "g14" {
-			t.Errorf("a call went to g14, which is not online: %+v", c)
-		}
-	}
-	// With no node online the key fails naming why; a node coming online builds it as a new revision.
-	r2 := newRig(t, goBundle)
-	r2.pres.Put("ace", nil, true)
-	r2.pres.Put("novox", nil, true)
-	if v := r2.consider(t, "modules/m"); v.State != delivery.BuildFailed || !strings.Contains(v.Error, "online") {
-		t.Fatalf("build = %+v, want failed because no node is online", v)
-	}
-	r2.pres.Put("ace", presenceValue(t, true), false)
-	r2.b.Reconsider(context.Background())
-	r2.b.Wait()
-	if v := valueOf(t, r2.st, r2.key); v.State != delivery.BuildDone {
-		t.Errorf("build = %+v, want done once a node is online", v)
-	}
-}
-
 func TestACandidatesImageIsPublishedOnceWhenTheTrunkNamesItsFingerprint(t *testing.T) { // review r1, mesh-delivery 1; ADR 0487 clause 5
 	r := newRig(t, imageArt)
-	r.b.Health = imageHave(t, "ace")
+	r.puller = "ace"
 	trunkModule(t, r) // the trunk carries another fingerprint; fp1 is the candidate's
 	r.b.Candidate(context.Background(), "feat%2Fx", candidateValue(t, "feat/x", 7, headX))
 	r.b.Wait()
@@ -590,7 +591,7 @@ func TestACandidatesImageIsPublishedOnceWhenTheTrunkNamesItsFingerprint(t *testi
 
 func TestAFailedPublishOfACandidatesImageIsWrittenToTheKey(t *testing.T) { // review r2, mesh-delivery 1; ADR 0487 clause 5
 	r := newRig(t, imageArt)
-	r.b.Health = imageHave(t, "ace")
+	r.puller = "ace"
 	trunkModule(t, r)
 	r.b.Candidate(context.Background(), "feat%2Fx", candidateValue(t, "feat/x", 7, headX))
 	r.b.Wait()
diff --git a/modules/mesh-delivery-builder/manifest_test.go b/modules/mesh-delivery-builder/manifest_test.go
index 6f13144..930b0d8 100644
--- a/modules/mesh-delivery-builder/manifest_test.go
+++ b/modules/mesh-delivery-builder/manifest_test.go
@@ -38,6 +38,7 @@ type manifest struct {
 	Consumes []string `json:"consumes"`
 	State    []state  `json:"state"`
 	Reads    []string `json:"reads"`
+	Uses     []string `json:"uses"`
 	Invokes  []string `json:"invokes"`
 	Config   map[string]struct {
 		Type        string `json:"type"`
@@ -86,12 +87,17 @@ func TestManifestDeclarations(t *testing.T) { // 1607/AC1
 	if want := []state{{Name: "builds", History: 5}, {Name: "instances", History: 1}}; !reflect.DeepEqual(m.State, want) { // delivery.BuilderBuildsHistory
 		t.Errorf("state = %+v, want %+v", m.State, want)
 	}
+	// 1887/A4c: the builder chooses no node, so it reads neither presence nor have, invokes no build module's tool and
+	// holds no capacity; it puts asks on the three build seats and reads their steps (ADR 0525 §1, §4, §5).
 	if want := []string{"mesh-build-go.steps", "mesh-build-go.toolchains", "mesh-build-image.steps", "mesh-build-node.steps", "mesh-build-node.toolchains",
-		"mesh-delivery-indexer.candidates", "mesh-delivery-indexer.manifests", "mesh-delivery-indexer.modules", "mesh-delivery-watchman.presence", "node-engine.have"}; !reflect.DeepEqual(sorted(m.Reads), want) {
+		"mesh-delivery-indexer.candidates", "mesh-delivery-indexer.manifests", "mesh-delivery-indexer.modules"}; !reflect.DeepEqual(sorted(m.Reads), want) {
 		t.Errorf("reads = %v, want %v", m.Reads, want)
 	}
-	if want := []string{"mesh-build-go.build_go_build", "mesh-build-go.build_go_fetch", "mesh-build-image.build_image_build", "mesh-build-image.build_image_copy", "mesh-build-image.build_image_fetch", "mesh-build-node.build_node_build", "mesh-build-node.build_node_fetch"}; !reflect.DeepEqual(sorted(m.Invokes), want) {
-		t.Errorf("invokes = %v, want only the build modules' fetch and build (go, image, node) and the image module's copy (ADR 0498 clause 4)", m.Invokes)
+	if want := []string{"node-build-go", "node-build-image", "node-build-node"}; !reflect.DeepEqual(sorted(m.Uses), want) {
+		t.Errorf("uses = %v, want the three build seats", m.Uses)
+	}
+	if len(m.Invokes) != 0 || len(m.Config) != 0 {
+		t.Errorf("invokes = %v, config = %v, want none: no tool call from the builder and no capacity", m.Invokes, m.Config)
 	}
 	// The builder is woken by a build module's report of a toolchain, as the indexer is: the bucket may not exist when it starts.
 	if want := []string{"mesh-build-go.toolchain.reported", "mesh-build-node.toolchain.reported"}; !reflect.DeepEqual(sorted(m.Consumes), want) {
@@ -103,7 +109,7 @@ func TestManifestDeclarations(t *testing.T) { // 1607/AC1
 	if m.SecretsOwner != "mesh-delivery-builder" {
 		t.Errorf("secrets-owner = %q", m.SecretsOwner)
 	}
-	for _, k := range []string{"streams", "logs", "emits", "claims", "provides", "requires", "uses", "defines-seats", "tools", "seat", "seats", "bus"} {
+	for _, k := range []string{"streams", "logs", "emits", "claims", "provides", "requires", "defines-seats", "tools", "seat", "seats", "bus", "invokes", "config"} {
 		if _, ok := top[k]; ok {
 			t.Errorf("the manifest declares %q: the builder has none", k)
 		}
@@ -129,35 +135,19 @@ func TestManifestProcess(t *testing.T) { // 1607/AC1
 		t.Errorf("process = %v", p)
 	}
 	env, _ := p["env"].(map[string]any)
-	// The build capacity of each node is the module's setting `capacity` (issue 1661, ADR 0478 clause 3), laid into the
-	// settings file the program reads; empty is one step at a time everywhere. The environment holds no capacity.
-	if len(env) != 2 || env["MESH_BROKER_FILE"] != "${dir:state}/broker" || env["MESH_BUILDER_SETTINGS"] != "${dir:state}/settings.json" {
-		t.Errorf("env = %v", p["env"])
+	if len(env) != 1 || env["MESH_BROKER_FILE"] != "${dir:state}/broker" {
+		t.Errorf("env = %v, want the broker file alone", p["env"])
 	}
-	if !reflect.DeepEqual(p["restart-on"], []any{"settings"}) {
-		t.Errorf("restart-on = %v, want the settings file, so a changed capacity reaches the running program", p["restart-on"])
-	}
-	c, ok := m.Config["capacity"]
-	if !ok || len(m.Config) != 1 || c.Type != "string" || c.Default != "shanks=3,ace=2,g14=0,novox=0" || c.Description == "" {
-		t.Errorf("config = %+v, want one string setting, capacity, shanks=3,ace=2,g14=0,novox=0 to start", m.Config)
-	}
-	var settings map[string]any
 	for _, r := range m.Resources {
 		if r["id"] == "settings" {
-			settings = r
+			t.Errorf("a settings resource %v: the builder holds no setting since the capacity is the build modules' (ADR 0525 §5)", r)
 		}
 	}
-	if settings == nil || settings["type"] != "file" || settings["merge"] != "json" || !reflect.DeepEqual(settings["takes-config"], []any{"capacity"}) || settings["path"] != "${dir:state}/settings.json" {
-		t.Errorf("settings resource = %v", settings)
-	}
-	if raw, err := os.ReadFile("files/settings.json"); err != nil || !strings.Contains(string(raw), `"capacity": "shanks=3,ace=2,g14=0,novox=0"`) {
-		t.Errorf("files/settings.json = %q, %v, want the setting's starting value", raw, err)
-	}
 	if _, bus := p["bus"]; bus {
 		t.Errorf("the process declares a bus: it runs on its own broker credential")
 	}
-	if len(m.Build.Artifacts) != 2 || m.Build.Artifacts[1].Name != "files" || m.Build.Artifacts[1].Kind != "archive" || m.Build.Artifacts[1].From != "files" {
-		t.Fatalf("artifacts = %+v, want the program and the files", m.Build.Artifacts)
+	if len(m.Build.Artifacts) != 1 {
+		t.Fatalf("artifacts = %+v, want the program alone", m.Build.Artifacts)
 	}
 	a := m.Build.Artifacts[0]
 	if st, err := os.Stat(a.From); err != nil || !st.IsDir() || a.Binary != "mesh-delivery-builder" || !strings.HasSuffix(a.From, a.Binary) || a.Kind != "bundle" || a.Language != "go" {
diff --git a/modules/mesh-delivery-builder/module.json b/modules/mesh-delivery-builder/module.json
index f18e708..798cb79 100644
--- a/modules/mesh-delivery-builder/module.json
+++ b/modules/mesh-delivery-builder/module.json
@@ -18,27 +18,14 @@
     "mesh-build-node.toolchains",
     "mesh-delivery-indexer.candidates",
     "mesh-delivery-indexer.manifests",
-    "mesh-delivery-indexer.modules",
-    "mesh-delivery-watchman.presence",
-    "node-engine.have"
+    "mesh-delivery-indexer.modules"
   ],
-  "invokes": [
-    "mesh-build-go.build_go_build",
-    "mesh-build-go.build_go_fetch",
-    "mesh-build-image.build_image_build",
-    "mesh-build-image.build_image_copy",
-    "mesh-build-image.build_image_fetch",
-    "mesh-build-node.build_node_build",
-    "mesh-build-node.build_node_fetch"
+  "uses": [
+    "node-build-go",
+    "node-build-image",
+    "node-build-node"
   ],
-  "config": {
-    "capacity": {
-      "type": "string",
-      "description": "How many build steps the builder runs at once on each node, as node=steps pairs separated by commas, such as shanks=3,ace=2 (ADR 0478 clause 3); a node set to 0 never builds, a node not named runs one at a time, and empty is one everywhere. The builder builds on shanks and ace only (the operator, 2026-10-21).",
-      "pattern": "|[a-z0-9_-]+=[0-9]+(,[a-z0-9_-]+=[0-9]+)*",
-      "default": "shanks=3,ace=2,g14=0,novox=0"
-    }
-  },
+
   "own-secrets": {
     "broker": "${dir:state}/broker"
   },
@@ -59,17 +46,6 @@
       "place": ".",
       "unknown": "program"
     },
-    {
-      "id": "settings",
-      "trusted": false,
-      "type": "file",
-      "path": "${dir:state}/settings.json",
-      "mode": "0600",
-      "owner": "mesh-delivery-builder",
-      "takes-config": ["capacity"],
-      "merge": "json",
-      "template": "files/settings.json"
-    },
     {
       "id": "builder",
       "type": "process",
@@ -79,12 +55,8 @@
         "./mesh-delivery-builder"
       ],
       "env": {
-        "MESH_BROKER_FILE": "${dir:state}/broker",
-        "MESH_BUILDER_SETTINGS": "${dir:state}/settings.json"
+        "MESH_BROKER_FILE": "${dir:state}/broker"
       },
-      "restart-on": [
-        "settings"
-      ],
       "user": "mesh-delivery-builder",
       "health": {
         "kind": "unit"
@@ -100,11 +72,6 @@
         "system": "arch",
         "from": "cmd/mesh-delivery-builder",
         "binary": "mesh-delivery-builder"
-      },
-      {
-        "name": "files",
-        "kind": "archive",
-        "from": "files"
       }
     ]
   }