diff --git a/modules/mesh-delivery-builder/buildrun/names.go b/modules/mesh-delivery-builder/buildrun/names.go
index 50ab553c..f42177cf 100644
--- a/modules/mesh-delivery-builder/buildrun/names.go
+++ b/modules/mesh-delivery-builder/buildrun/names.go
@@ -11,6 +11,3 @@ const (
 
 // StepsBucket is the bucket of a build module's state steps.
 func StepsBucket(module string) string { return module + "_steps" }
-
-// ToolchainsBucket is the bucket of a build module's state toolchains.
-func ToolchainsBucket(module string) string { return module + "_toolchains" }
diff --git a/modules/mesh-delivery-builder/buildrun/standing.go b/modules/mesh-delivery-builder/buildrun/standing.go
index f97ae7c0..52a490b1 100644
--- a/modules/mesh-delivery-builder/buildrun/standing.go
+++ b/modules/mesh-delivery-builder/buildrun/standing.go
@@ -3,9 +3,6 @@ package buildrun
 import (
 	"context"
 	"errors"
-	"fmt"
-	"maps"
-	"slices"
 	"sort"
 	"sync"
 	"time"
@@ -15,120 +12,60 @@ import (
 	"git.novox.be/novox/mesh-contracts/go/clients/meshmoduleassignerclient"
 	"git.novox.be/novox/mesh-delivery/contracts/go/clients/meshwantsclient"
 	meshwants "git.novox.be/novox/mesh-delivery/contracts/go/seats/meshwants"
-	"git.novox.be/novox/mesh-delivery/sdk/buildstep"
 	"git.novox.be/novox/mesh-sdk/go/process"
 )
 
-// A build module writes <node>.<language> of its toolchains state on every node it runs on, and nothing deletes the key
-// when the module leaves a node: no part writes another module's state, and the module is gone. A report of a node the
-// build module no longer runs on is therefore no builder's (issue 1940: mesh-build-node taken off ace on 2026-10-23 left
-// ace.typescript at v26.12.0, and every Node fingerprint said "builders disagree").
-//
-// ToolchainGate stands between the toolchains buckets and what takes their entries in (the indexer's PutToolchain, a
-// ToolchainSet): an entry is passed on only while the assignments (the seat mesh-module-assigner's state `assignments`, held by
-// the assigner, AssignmentsBucket, read by meshmoduleassignerclient.Placed; ADR 0567, ADR 0549 §3) places its build module on
-// its node, and only once it was written since that assignments; it is passed on as deleted otherwise, said once, and
-// passed on when its node writes it again. A report written before the assignments is one an earlier run of the module
-// left (issue 1940, 2026-10-25 20:56: mesh-build-node put on ace again brought ace.typescript v26.12.0 of 2026-10-23
-// back into the agreement before the module ran there). Until the assignments is settled, and while no node's assignments
-// is held (before the assigner's adopt writes the first one, or where the state cannot be read), every entry is passed
-// on. Builders that run and report different versions still disagree: that refusal is the guard of novox/hq ADR 0465,
-// and it stays.
-//
-// This replaces the copies of the gate the indexer, the builder and the checker each kept over the controller's
-// assignments (issue 1940's subtask, issue 774: those go with the controller's lease, ADR 0549 §6).
-type ToolchainGate struct {
-	mu      sync.Mutex
-	modules map[string]bool                                           // the build modules whose toolchains pass the gate
-	forward func(module, key string, value []byte, deleted bool) bool // answers whether it changed what it holds
-	logf    func(format string, a ...any)
-	placed  placements
-	known   bool                         // the assignments is settled
-	raw     map[string]map[string][]byte // module -> toolchains key -> value, as the bucket holds it
-	left    map[string]string            // <module>/<key> -> why it was said left out, so each reason is said once
-	// OnPlaced is told, outside the gate's lock, once the assignments's history is read and after each revision of it
+// PlacedNodes holds which modules the catalogue places on which node: the seat mesh-module-assigner's state `assignments`,
+// held by the assigner (AssignmentsBucket, read by meshmoduleassignerclient.Placed; ADR 0567), or the assignment half
+// (meshwantsclient.Placed, fed by Revision). The builder counts the nodes it names (Nodes; ADR 0624 §1). It holds no
+// toolchain: the builder keeps the toolchains it heard in its state toolchains-heard and forgets one when the node-engine
+// seat says the build module stopped on the node, never on a placement (design 47 G §546).
+type PlacedNodes struct {
+	mu     sync.Mutex
+	logf   func(format string, a ...any)
+	placed placements
+	known  bool // the assignments is settled
+	// OnPlaced is told, outside the lock, once the assignments's history is read and after each revision of it
 	// FollowAssignments hears from then on (the counted nodes, Nodes, may have changed). Nil tells nobody.
 	OnPlaced func()
 }
 
-// placements is where the gate reads which modules stand on which node, and since when: the assigner's state
-// (meshmoduleassignerclient.Placed, fed by Assignments) or the assignment half (meshwantsclient.Placed, fed by Revision).
+// placements is where the part reads which modules stand on which node.
 type placements interface {
 	Seeded() bool
-	Since(node, module string) (time.Time, bool)
 	ByNode() map[string][]string
 }
 
-// NewToolchainGate is a gate over the toolchains of modules, passing what stands on to forward and saying with logf what
-// it leaves out.
-func NewToolchainGate(modules []string, forward func(module, key string, value []byte, deleted bool) bool, logf func(string, ...any)) *ToolchainGate {
-	g := &ToolchainGate{modules: map[string]bool{}, forward: forward, logf: logf, placed: meshmoduleassignerclient.NewPlaced(),
-		raw: map[string]map[string][]byte{}, left: map[string]string{}}
-	for _, m := range modules {
-		g.modules[m] = true
-	}
-	return g
+// NewPlacedNodes is the placements of the builder, saying with logf what it cannot read.
+func NewPlacedNodes(logf func(string, ...any)) *PlacedNodes {
+	return &PlacedNodes{logf: logf, placed: meshmoduleassignerclient.NewPlaced()}
 }
 
-// UseModules replaces the build modules whose reports the gate passes on again when the assignments moves (a part that
-// finds them from the seat list and the manifests, as the indexer does, gives them at each change), and passes every
-// report it holds on again. It answers whether what it passed on changed.
-func (g *ToolchainGate) UseModules(modules []string) bool {
-	g.mu.Lock()
-	defer g.mu.Unlock()
-	g.modules = map[string]bool{}
-	for _, m := range modules {
-		g.modules[m] = true
-	}
-	return g.all()
-}
-
-// Toolchain takes one change of a build module's toolchains bucket in and answers whether what it passed on changed.
-func (g *ToolchainGate) Toolchain(module, key string, value []byte, deleted bool) bool {
-	g.mu.Lock()
-	defer g.mu.Unlock()
-	if g.raw[module] == nil {
-		g.raw[module] = map[string][]byte{}
-	}
-	if deleted {
-		delete(g.raw[module], key)
-	} else {
-		g.raw[module][key] = value
-	}
-	return g.pass(module, key)
-}
-
-// Assignments takes one revision of the seat mesh-module-assigner's assignments in (at is when the bus wrote it) and answers whether what it
-// passed on changed. A value that does not read is said, and places nothing on its node.
-func (g *ToolchainGate) Assignments(key string, value []byte, deleted bool, at time.Time) bool {
+// Assignments takes one revision of the seat mesh-module-assigner's assignments in (at is when the bus wrote it) and
+// answers whether the nodes the modules stand on changed. A value that does not read is said, and places nothing.
+func (g *PlacedNodes) Assignments(key string, value []byte, deleted bool, at time.Time) bool {
 	g.mu.Lock()
 	defer g.mu.Unlock()
 	placed, ok := g.placed.(*meshmoduleassignerclient.Placed)
 	if !ok {
-		g.logf("%s: %s is not read, the gate takes the assignment half (design 47)", AssignmentsBucket, key)
+		g.logf("%s: %s is not read, the placements take the assignment half (design 47)", AssignmentsBucket, key)
 		return false
 	}
 	was := placed.Seeded()
-	node, changed, err := placed.Put(key, value, deleted, at)
+	_, changed, err := placed.Put(key, value, deleted, at)
 	if err != nil {
 		g.logf("%s: %v (issue 1940)", AssignmentsBucket, err)
 	}
 	if !g.known {
 		return false
 	}
-	if was != g.placed.Seeded() {
-		// The first assignments came, or the last went: every report's standing changed.
-		return g.all()
-	}
-	return g.again(node, changed)
+	return was != g.placed.Seeded() || len(changed) > 0
 }
 
 // Revision takes one assignment graph revision the part's view holds in (design 47 *Each part acts on its own entries*:
-// the placements come from the seat mesh-wants' assignment half, never the assigner's state; assignmentview's Held hands
-// each) and answers whether what it passed on changed. The first revision taken settles the gate, as the assignments'
-// history read does; a later one passes on again the reports of each node whose build modules' standing changed. A gate
-// fed by Revision reads no Assignments.
-func (g *ToolchainGate) Revision(r meshwants.AssignmentRevision) bool {
+// the placements come from the seat mesh-wants' assignment half, never the assigner's state) and answers whether the
+// nodes the modules stand on changed. The first revision taken settles it. Placements fed by Revision read no Assignments.
+func (g *PlacedNodes) Revision(r meshwants.AssignmentRevision) bool {
 	g.mu.Lock()
 	defer g.mu.Unlock()
 	placed, ok := g.placed.(*meshwantsclient.Placed)
@@ -141,20 +78,14 @@ func (g *ToolchainGate) Revision(r meshwants.AssignmentRevision) bool {
 	if changed == nil {
 		return false
 	}
-	if !g.known || was != placed.Seeded() {
-		g.known = true
-		return g.all()
-	}
-	moved := false
-	for _, node := range slices.Sorted(maps.Keys(changed)) {
-		moved = g.again(node, changed[node]) || moved
-	}
-	return moved
+	first := !g.known
+	g.known = true
+	return first || was != placed.Seeded() || len(changed) > 0
 }
 
 // Nodes are the nodes the assignments places any module on, sorted: the nodes the mesh counts (a node leaves the count
 // when the assignments no longer names it; ADR 0624 §1). None until the assignments is read.
-func (g *ToolchainGate) Nodes() []string {
+func (g *PlacedNodes) Nodes() []string {
 	var out []string
 	for node, modules := range g.placed.ByNode() {
 		if len(modules) > 0 {
@@ -165,95 +96,27 @@ func (g *ToolchainGate) Nodes() []string {
 	return out
 }
 
-// Settled says the assignments's history is read: from now on only the reports of placed nodes pass, once a node's
-// assignments is held. It answers whether what it passed on changed.
-func (g *ToolchainGate) Settled() bool {
+// Settled says the assignments's history is read.
+func (g *PlacedNodes) Settled() {
 	g.mu.Lock()
 	defer g.mu.Unlock()
 	g.known = true
-	return g.all()
-}
-
-// all passes on every report again. The caller holds mu.
-func (g *ToolchainGate) all() bool {
-	changed := false
-	for _, module := range slices.Sorted(maps.Keys(g.raw)) {
-		for _, k := range slices.Sorted(maps.Keys(g.raw[module])) {
-			changed = g.pass(module, k) || changed
-		}
-	}
-	return changed
-}
-
-// again passes on every report of node by a build module among modules. The caller holds mu.
-func (g *ToolchainGate) again(node string, modules []string) bool {
-	changed := false
-	for _, module := range modules {
-		if !g.modules[module] {
-			continue
-		}
-		for _, k := range slices.Sorted(maps.Keys(g.raw[module])) {
-			if n, _, err := buildstep.ParseToolchainKey(k); err == nil && n == node {
-				changed = g.pass(module, k) || changed
-			}
-		}
-	}
-	return changed
-}
-
-// pass hands one key on as it stands: its value when its node is placed and wrote it since (or the assignments is not
-// known), deleted otherwise. The caller holds mu.
-func (g *ToolchainGate) pass(module, key string) bool {
-	value, held := g.raw[module][key]
-	if !held {
-		return g.forward(module, key, nil, true)
-	}
-	node, _, err := buildstep.ParseToolchainKey(key)
-	why := ""
-	if err == nil && g.known && g.placed.Seeded() {
-		why = g.leftOut(module, node, value)
-	}
-	if why == "" {
-		delete(g.left, module+"/"+key)
-		return g.forward(module, key, value, false)
-	}
-	if g.left[module+"/"+key] != why {
-		g.left[module+"/"+key] = why
-		g.logf("%s.%s is left out of the agreed toolchain: %s (issue 1940)", ToolchainsBucket(module), key, why)
-	}
-	return g.forward(module, key, nil, true)
-}
-
-// leftOut is why a node's report is no builder's, or empty when it counts: the catalogue does not place the module on its
-// node, or the report was written before it did. A value that is no toolchain is passed on for its reader to refuse.
-// The caller holds mu.
-func (g *ToolchainGate) leftOut(module, node string, value []byte) string {
-	since, placed := g.placed.Since(node, module)
-	if !placed {
-		return fmt.Sprintf("the catalogue does not place %s on %s, so it is no builder", module, node)
-	}
-	tc, err := buildstep.DecodeToolchain(value)
-	if err == nil && tc.At.Before(since) {
-		return fmt.Sprintf("it was written at %s, before %s was placed on %s at %s: it counts once %s writes it again",
-			tc.At.UTC().Format(time.RFC3339), module, node, since.UTC().Format(time.RFC3339), node)
-	}
-	return ""
 }
 
 // FollowAssignments reads the seat mesh-module-assigner's assignments with its history into gate, says it settled, and follows it; changed
 // is told whenever what the gate passes on changed. Where the state cannot be read or watched (not there, or this part
 // may not read it) it says so and the gate passes every report on: not fatal, since an indexer, builder or checker that
 // stops for it stops every delivery (issue 1945). An error of the watch after that ends on the channel.
-func FollowAssignments(ctx context.Context, js process.BucketOpener, gate *ToolchainGate, changed func(context.Context), logf func(string, ...any)) (<-chan error, error) {
+func FollowAssignments(ctx context.Context, js process.BucketOpener, gate *PlacedNodes, changed func(context.Context), logf func(string, ...any)) (<-chan error, error) {
 	errs := make(chan error, 1)
 	kv, err := js.KeyValue(ctx, AssignmentsBucket)
 	if err != nil {
-		logf("the state %s cannot be read, so every node's toolchain report counts, a build node's the catalogue does not place too (issue 1940): %v", AssignmentsBucket, err)
+		logf("the state %s cannot be read, so no node is counted by the assignments: %v", AssignmentsBucket, err)
 		return errs, nil
 	}
 	w, err := kv.WatchAll(ctx, jetstream.IncludeHistory())
 	if err != nil {
-		logf("the state %s cannot be watched, so every node's toolchain report counts, a build node's the catalogue does not place too (issue 1940): %v", AssignmentsBucket, err)
+		logf("the state %s cannot be watched, so no node is counted by the assignments: %v", AssignmentsBucket, err)
 		return errs, nil
 	}
 	put := func(e jetstream.KeyValueEntry) bool {
@@ -275,9 +138,8 @@ func FollowAssignments(ctx context.Context, js process.BucketOpener, gate *Toolc
 			put(e)
 		}
 	}
-	if gate.Settled() {
-		changed(ctx)
-	}
+	gate.Settled()
+	changed(ctx)
 	if gate.OnPlaced != nil {
 		gate.OnPlaced()
 	}
diff --git a/modules/mesh-delivery-builder/buildrun/standing_test.go b/modules/mesh-delivery-builder/buildrun/standing_test.go
index 5fca15d6..2b8da16f 100644
--- a/modules/mesh-delivery-builder/buildrun/standing_test.go
+++ b/modules/mesh-delivery-builder/buildrun/standing_test.go
@@ -4,7 +4,6 @@ import (
 	"bytes"
 	"context"
 	"errors"
-	"fmt"
 	"log"
 	"strings"
 	"testing"
@@ -15,19 +14,8 @@ import (
 	"git.novox.be/novox/mesh-contracts/go/clients/meshmoduleassignerclient"
 	"git.novox.be/novox/mesh-contracts/go/seats/meshmoduleassigner"
 	meshwants "git.novox.be/novox/mesh-delivery/contracts/go/seats/meshwants"
-	"git.novox.be/novox/mesh-delivery/sdk/buildstep"
 )
 
-func gateReport(t *testing.T, node, version string, at time.Time) (string, []byte) {
-	t.Helper()
-	key, _ := buildstep.ToolchainKey(node, "typescript")
-	value, err := buildstep.EncodeToolchain(buildstep.Toolchain{Language: "typescript", Version: version, Recipe: "f59571cf4be75adf", At: at})
-	if err != nil {
-		t.Fatal(err)
-	}
-	return key, value
-}
-
 // placing is a value of the state `assignments` placing modules on node.
 func placing(t *testing.T, node string, modules ...string) (string, []byte) {
 	t.Helper()
@@ -43,219 +31,52 @@ func placing(t *testing.T, node string, modules ...string) (string, []byte) {
 	return key, values[key]
 }
 
-func agreedOf(set *ToolchainSet) (string, string) {
-	tc, none := buildstep.AgreedToolchain(set.Entries("typescript"))
-	return tc.Version, none
-}
-
-// Issue 1940, the gate over the catalogue's assignments (issue 774, ADR 0549 §3): a build node's report counts only while
-// the assignments places its build module on its node, and only once written since; before the assignments is settled, and
-// while no node's assignments is held, every report counts. The live cases: mesh-build-node taken off ace left
-// ace.typescript at v26.12.0 against v26.12.1 on the three others; put on ace again, its report of 2026-10-23 06:29 came
-// back before the module ran there.
-func TestToolchainGate(t *testing.T) {
-	old := time.Date(2026, 10, 23, 6, 29, 18, 0, time.UTC)     // ace's report from its earlier run
-	placed := time.Date(2026, 10, 25, 19, 56, 45, 0, time.UTC) // mesh-build-node placed on ace again
+// The placements the builder counts nodes by (ADR 0624 §1): a settled assignments names the nodes its modules stand on, a
+// revision of the assignment half the same; they hold no toolchain (design 47 G §546: a toolchain is forgotten on the
+// node-engine seat's stopped, never on a placement).
+func TestPlacedNodes(t *testing.T) {
+	old := time.Date(2026, 10, 23, 6, 29, 18, 0, time.UTC)
 	three := []string{"g14", "novox", "shanks"}
-	start := func(t *testing.T, seeded bool) (*ToolchainGate, *ToolchainSet, *[]string) {
-		set := &ToolchainSet{}
-		said := &[]string{}
-		gate := NewToolchainGate([]string{GoBuildModule, NodeBuildModule}, set.Put, func(f string, a ...any) { *said = append(*said, fmt.Sprintf(f, a...)) })
+
+	t.Run("the assignments names the counted nodes once it is settled", func(t *testing.T) {
+		gate := NewPlacedNodes(func(string, ...any) {})
 		for _, node := range three {
-			if seeded {
-				key, value := placing(t, node, NodeBuildModule)
-				gate.Assignments(key, value, false, old.Add(-time.Hour))
+			k, v := placing(t, node, NodeBuildModule)
+			if gate.Assignments(k, v, false, old) {
+				t.Fatal("an assignments before it is settled changed the counted nodes")
 			}
-			key, value := gateReport(t, node, "v26.12.1", placed.Add(time.Minute))
-			gate.Toolchain(NodeBuildModule, key, value, false)
 		}
-		return gate, set, said
-	}
-
-	t.Run("not placed on ace: its report is no builder's", func(t *testing.T) {
-		gate, set, said := start(t, true)
-		key, value := gateReport(t, "ace", "v26.12.0", old)
-		gate.Toolchain(NodeBuildModule, key, value, false)
-		if a := buildstep.ToolchainAgreement(set.Entries("typescript")); len(a.SittingOut) != 1 || a.SittingOut[0].Node != "ace" { // ADR 0584: the majority is agreed, ace's report counts as the one that sits out
-			t.Fatalf("before the assignments is settled every report counts; got %+v", a)
-		}
-		k, v := placing(t, "ace", GoBuildModule) // another build module on ace: no matter
-		gate.Assignments(k, v, false, old)
-		if !gate.Settled() {
-			t.Fatal("settling left ace's report out, so what was passed on changed")
-		}
-		if v, none := agreedOf(set); v != "v26.12.1" || none != "" {
-			t.Fatalf("the placed nodes agree on v26.12.1; got %q, %q", v, none)
-		}
-		if len(*said) != 1 || !strings.Contains((*said)[0], "does not place mesh-build-node on ace") {
-			t.Fatalf("ace's report is said left out once; said %q", *said)
-		}
-		if gate.Toolchain(NodeBuildModule, key, value, false) {
-			t.Fatal("a report of a node not placed changed what was passed on")
-		}
-		// Placed on ace with a report written since: it counts, and the builders really disagree.
-		k, v = placing(t, "ace", GoBuildModule, NodeBuildModule)
-		gate.Assignments(k, v, false, old.Add(-time.Minute))
-		if a := buildstep.ToolchainAgreement(set.Entries("typescript")); a.Toolchain.Version != "v26.12.1" || len(a.SittingOut) != 1 || a.SittingOut[0].Version != "v26.12.0" {
-			t.Fatalf("builders that run different versions: the majority is agreed and ace sits out; got %+v", a)
-		}
-		// Taken off ace again (its key deleted): its report goes again.
-		if !gate.Assignments(k, nil, true, placed) {
-			t.Fatal("taking ace's assignments away passed nothing on")
-		}
-		if v, none := agreedOf(set); v != "v26.12.1" || none != "" {
-			t.Fatalf("got %q, %q", v, none)
-		}
-		// A report deleted from the bucket goes whether its node is placed or not.
-		key, _ = gateReport(t, "g14", "v26.12.1", placed)
-		if !gate.Toolchain(NodeBuildModule, key, nil, true) || len(set.Entries("typescript")) != 2 {
-			t.Fatalf("deleting g14's report: %d entries left, want novox and shanks", len(set.Entries("typescript")))
-		}
-	})
-
-	t.Run("build modules given later pass their reports on when the assignments moves", func(t *testing.T) {
-		set := &ToolchainSet{}
-		gate := NewToolchainGate(nil, set.Put, func(string, ...any) {})
 		gate.Settled()
-		k, v := placing(t, "novox", GoBuildModule)
-		gate.Assignments(k, v, false, old)
-		key, value := gateReport(t, "ace", "v26.12.1", placed.Add(time.Minute))
-		gate.Toolchain(NodeBuildModule, key, value, false) // ace is not placed: left out
-		k, v = placing(t, "ace", NodeBuildModule)
-		if gate.Assignments(k, v, false, placed) || len(set.Entries("typescript")) != 0 {
-			t.Fatalf("a module the gate was not given passed on at the assignments: %v", set.Entries("typescript"))
+		if got := strings.Join(gate.Nodes(), ","); got != "g14,novox,shanks" {
+			t.Fatalf("nodes = %q", got)
 		}
-		if !gate.UseModules([]string{NodeBuildModule}) || len(set.Entries("typescript")) != 1 {
-			t.Fatalf("given mesh-build-node, ace's report placed since is passed on; entries %v", set.Entries("typescript"))
+		k, v := placing(t, "ace", GoBuildModule)
+		if !gate.Assignments(k, v, false, old) || len(gate.Nodes()) != 4 {
+			t.Fatalf("ace placed: nodes %v", gate.Nodes())
+		}
+		if !gate.Assignments(k, nil, true, old.Add(time.Hour)) || len(gate.Nodes()) != 3 {
+			t.Fatalf("ace's assignments deleted: nodes %v", gate.Nodes())
 		}
 	})
 
-	for _, c := range []struct {
-		name   string
-		at     time.Time // when ace wrote its report
-		counts bool
-	}{
-		{"a report left before the assignments", old, false},
-		{"a report written since the assignments", placed.Add(30 * time.Second), true},
-	} {
-		t.Run(c.name, func(t *testing.T) {
-			gate, set, said := start(t, true)
-			k, v := placing(t, "ace") // ace's key, first heard placing nothing
-			gate.Assignments(k, v, false, old.Add(-time.Hour))
-			gate.Settled()
-			k, v = placing(t, "ace", NodeBuildModule)
-			if gate.Assignments(k, v, false, placed) {
-				t.Fatal("assignments with no report passed something on")
-			}
-			key, value := gateReport(t, "ace", "v26.12.0", c.at)
-			if got := gate.Toolchain(NodeBuildModule, key, value, false); got != c.counts {
-				t.Fatalf("ace's report passed on: %v, want %v", got, c.counts)
-			}
-			// ace's assignments written again with another module beside: its standing does not move, nothing is said again.
-			k, v = placing(t, "ace", GoBuildModule, NodeBuildModule)
-			if gate.Assignments(k, v, false, placed.Add(time.Minute)) {
-				t.Fatal("the same assignments of mesh-build-node changed what was passed on")
-			}
-			if c.counts {
-				return
-			}
-			if v, none := agreedOf(set); v != "v26.12.1" || none != "" {
-				t.Fatalf("ace's left report is no builder's; got %q, %q", v, none)
-			}
-			if len(*said) != 1 || !strings.Contains((*said)[0], "before mesh-build-node was placed on ace at 2026-10-25T19:56:45Z") {
-				t.Fatalf("said %q, want once why ace's report is left out", *said)
-			}
-			key, value = gateReport(t, "ace", "v26.12.1", placed.Add(time.Minute))
-			if !gate.Toolchain(NodeBuildModule, key, value, false) || len(set.Entries("typescript")) != 4 {
-				t.Fatal("ace's new report was not passed on")
-			}
-		})
-	}
-
-	t.Run("no assignments held: every report counts", func(t *testing.T) {
-		gate, set, _ := start(t, false)
-		key, value := gateReport(t, "ace", "v26.12.0", old)
-		gate.Toolchain(NodeBuildModule, key, value, false)
-		gate.Settled()
-		if n := len(set.Entries("typescript")); n != 4 {
-			t.Fatalf("before the first assignments file every report counts; got %d", n)
-		}
-		k, v := placing(t, "g14", NodeBuildModule)
-		if !gate.Assignments(k, v, false, old.Add(-time.Hour)) || len(set.Entries("typescript")) != 1 {
-			t.Fatalf("the first assignments leaves every node it does not place out; got %d", len(set.Entries("typescript")))
-		}
-		if !gate.Assignments(k, nil, true, placed) || len(set.Entries("typescript")) != 4 {
-			t.Fatal("the last assignments gone: every report counts again")
-		}
-	})
-
-	// Design 47 *Each part acts on its own entries*: fed by the assignment half's revisions, the gate settles at the first,
-	// leaves out a node no revision places the build module on, and counts a node placed in a later revision only by a
-	// report written since that revision's time.
-	t.Run("fed by the assignment half", func(t *testing.T) {
-		set := &ToolchainSet{}
-		said := &[]string{}
-		gate := NewToolchainGate([]string{GoBuildModule, NodeBuildModule}, set.Put, func(f string, a ...any) { *said = append(*said, fmt.Sprintf(f, a...)) })
-		for _, node := range append([]string{"ace"}, three...) {
-			key, value := gateReport(t, node, "v26.12.1", placed.Add(time.Minute))
-			if node == "ace" {
-				key, value = gateReport(t, node, "v26.12.0", old)
-			}
-			gate.Toolchain(NodeBuildModule, key, value, false)
-		}
-		revision := func(n int64, at time.Time, nodes ...string) meshwants.AssignmentRevision {
+	t.Run("the assignment half: the first revision settles, a later one moves the nodes", func(t *testing.T) {
+		gate := NewPlacedNodes(func(string, ...any) {})
+		revision := func(n int64, nodes ...string) meshwants.AssignmentRevision {
+			at := old.Add(time.Duration(n) * time.Hour)
 			r := meshwants.AssignmentRevision{Revision: n, Kind: "trunk", At: &at}
 			for _, node := range nodes {
 				r.Entries = append(r.Entries, meshwants.NodeEntryRef{Node: node, Module: NodeBuildModule, Digest: "d-" + node})
 			}
 			return r
 		}
-		if !gate.Revision(revision(7, old.Add(-time.Hour), three...)) || len(set.Entries("typescript")) != 3 {
-			t.Fatalf("the first revision settles the gate and leaves ace out; %d entries", len(set.Entries("typescript")))
+		if !gate.Revision(revision(7, three...)) || len(gate.Nodes()) != 3 {
+			t.Fatalf("the first revision: nodes %v", gate.Nodes())
 		}
-		if gate.Revision(revision(7, old.Add(-time.Hour), three...)) {
-			t.Fatal("the same revision again changed what was passed on")
+		if gate.Revision(revision(7, three...)) {
+			t.Fatal("the same revision again changed the counted nodes")
 		}
-		if gate.Revision(revision(8, placed, "ace", "g14", "novox", "shanks")); len(set.Entries("typescript")) != 3 {
-			t.Fatal("ace's report from before revision 8 placed it counts")
-		}
-		if len(*said) < 2 || !strings.Contains((*said)[len(*said)-1], "before mesh-build-node was placed on ace at 2026-10-25T19:56:45Z") {
-			t.Fatalf("said %q, want why ace's old report is left out", *said)
-		}
-		key, value := gateReport(t, "ace", "v26.12.1", placed.Add(time.Minute))
-		if !gate.Toolchain(NodeBuildModule, key, value, false) || len(set.Entries("typescript")) != 4 {
-			t.Fatal("ace's report written since revision 8 is not passed on")
-		}
-		if !gate.Revision(revision(9, placed.Add(time.Hour), "ace", "novox", "shanks")) || len(set.Entries("typescript")) != 3 || len(gate.Nodes()) != 3 {
-			t.Fatalf("g14 taken off in revision 9: %d entries, nodes %v", len(set.Entries("typescript")), gate.Nodes())
-		}
-	})
-
-	t.Run("the history: a module in the first revision heard of a key stands since before it", func(t *testing.T) {
-		p := meshmoduleassignerclient.NewPlaced()
-		// ace's node key is the first revision heard of it: its module stands since before.
-		k, v := placing(t, "ace", NodeBuildModule)
-		p.Put(k, v, false, old)
-		if _, changed, _ := p.Put("ace."+NodeBuildModule, []byte("{}"), false, placed); len(changed) != 0 {
-			t.Errorf("a module key says which modules stand: %v", changed)
-		}
-		k2, v2 := placing(t, "g14")
-		p.Put(k2, v2, false, old)
-		k2, v2 = placing(t, "g14", NodeBuildModule)
-		if _, changed, _ := p.Put(k2, v2, false, placed); strings.Join(changed, ",") != NodeBuildModule {
-			t.Errorf("a module placed says changed %v", changed)
-		}
-		if _, _, err := p.Put("novox.node", []byte("not json"), false, old); err == nil {
-			t.Error("a value that does not read was not said")
-		}
-		if s, ok := p.Since("ace", NodeBuildModule); !ok || !s.IsZero() {
-			t.Errorf("ace's module stands since %v, %v; want the zero time", s, ok)
-		}
-		if s, ok := p.Since("g14", NodeBuildModule); !ok || !s.Equal(placed) {
-			t.Errorf("g14's module stands since %v, %v; want the revision that placed it", s, ok)
-		}
-		if got := p.PlacedNodes(NodeBuildModule); strings.Join(got, ",") != "ace,g14" || len(p.ByNode()) != 2 || !p.Seeded() {
-			t.Errorf("PlacedNodes = %v, ByNode = %v", got, p.ByNode())
+		if !gate.Revision(revision(9, "novox", "shanks")) || len(gate.Nodes()) != 2 {
+			t.Fatalf("g14 taken off: nodes %v", gate.Nodes())
 		}
 	})
 
@@ -263,7 +84,7 @@ func TestToolchainGate(t *testing.T) {
 		var logs bytes.Buffer
 		logger := log.New(&logs, "", 0)
 		refused := errors.New("nats: permissions violation for publish to $JS.API.CONSUMER.CREATE.KV_mesh-delivery-assigner_assignments")
-		gate, _, _ := start(t, false)
+		gate := NewPlacedNodes(logger.Printf)
 		for _, bus := range []refusingBus{{err: refused}, {refuseOpen: true, err: refused}} {
 			if _, err := FollowAssignments(context.Background(), bus, gate, func(context.Context) {}, logger.Printf); err != nil {
 				t.Errorf("a refused assignments stopped the start: %v", err)
diff --git a/modules/mesh-delivery-builder/buildrun/toolchains.go b/modules/mesh-delivery-builder/buildrun/toolchains.go
index a37200b9..ba2368c6 100644
--- a/modules/mesh-delivery-builder/buildrun/toolchains.go
+++ b/modules/mesh-delivery-builder/buildrun/toolchains.go
@@ -1,55 +1,54 @@
 package buildrun
 
 import (
+	"sort"
 	"sync"
 
 	"git.novox.be/novox/mesh-delivery/sdk/buildstep"
 )
 
-// LanguageOf is the language each build module's toolchains state holds (the indexer's ToolchainModules, reversed).
+// LanguageOf is the language each build module's toolchain reports hold.
 var LanguageOf = map[string]string{GoBuildModule: "go", NodeBuildModule: "typescript"}
 
-// ToolchainSet holds what the build modules' toolchains buckets hold: each node's entry of a language, as the watches
-// put them in. Safe for use from the watches and from a build at once.
+// ToolchainsHeardState is the builder's old state section of the toolchains it heard (design 47 G §604, §546): one key
+// <node>.<language>, the toolchain as the build seat said it.
+const (
+	ToolchainsHeardState  = "toolchains-heard"
+	ToolchainsHeardBucket = "mesh-delivery-builder_" + ToolchainsHeardState
+)
+
+// ToolchainSet holds each node's toolchain of a language, as the builder heard it (design 47 G §604). Safe for use from
+// the consumer and from a build at once.
 type ToolchainSet struct {
 	mu sync.Mutex
 	by map[string]map[string]buildstep.Toolchain // language -> node -> entry
 }
 
-// Put takes a change of a build module's toolchains bucket in: a put of a node's entry (key <node>.<language>) or its
-// delete. It answers whether the language's entries changed (a node's version or recipe, or a node appearing or going).
-// A key or a value that is not an entry of the module's language is left out.
-func (s *ToolchainSet) Put(module, key string, value []byte, deleted bool) bool {
-	language, ok := LanguageOf[module]
-	if !ok {
-		return false
-	}
-	node, keyLanguage, err := buildstep.ParseToolchainKey(key)
-	if err != nil || keyLanguage != language {
-		return false
-	}
+// Set takes a node's toolchain in and answers whether the language's entries changed (a node's version, recipe or
+// digest, or a node appearing).
+func (s *ToolchainSet) Set(node string, tc buildstep.Toolchain) bool {
 	s.mu.Lock()
 	defer s.mu.Unlock()
-	if deleted {
-		if _, had := s.by[language][node]; !had {
-			return false
-		}
-		delete(s.by[language], node)
-		return true
-	}
-	tc, err := buildstep.DecodeToolchain(value)
-	if err != nil || tc.Language != language {
-		return false
-	}
 	if s.by == nil {
 		s.by = map[string]map[string]buildstep.Toolchain{}
 	}
-	if s.by[language] == nil {
-		s.by[language] = map[string]buildstep.Toolchain{}
+	if s.by[tc.Language] == nil {
+		s.by[tc.Language] = map[string]buildstep.Toolchain{}
 	}
-	cur, had := s.by[language][node]
-	s.by[language][node] = tc
-	return !had || cur.Version != tc.Version || cur.Recipe != tc.Recipe
+	cur, had := s.by[tc.Language][node]
+	s.by[tc.Language][node] = tc
+	return !had || cur.Version != tc.Version || cur.Recipe != tc.Recipe || cur.Digest != tc.Digest
+}
+
+// Delete takes a node's toolchain of a language out and answers whether it was held.
+func (s *ToolchainSet) Delete(node, language string) bool {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	if _, had := s.by[language][node]; !had {
+		return false
+	}
+	delete(s.by[language], node)
+	return true
 }
 
 // Entries are the nodes' entries of a language, in no particular order.
@@ -62,3 +61,33 @@ func (s *ToolchainSet) Entries(language string) []buildstep.NodeToolchain {
 	}
 	return out
 }
+
+// AgreedDigest is a digest of the agreed version and the nodes reporting it.
+type AgreedDigest struct {
+	Digest string
+	Nodes  []string
+}
+
+// Digests are the digests the nodes reporting the agreed toolchain's version report, sorted by digest, each with its
+// nodes sorted (design 47 G §472, §574). A node that reports no digest is left out.
+func Digests(entries []buildstep.NodeToolchain, agreed buildstep.Toolchain) []AgreedDigest {
+	by := map[string][]string{}
+	for _, e := range entries {
+		if e.Version == agreed.Version && e.Recipe == agreed.Recipe && e.Digest != "" {
+			by[e.Digest] = append(by[e.Digest], e.Node)
+		}
+	}
+	out := make([]AgreedDigest, 0, len(by))
+	for d, nodes := range by {
+		sort.Strings(nodes)
+		out = append(out, AgreedDigest{Digest: d, Nodes: nodes})
+	}
+	sort.Slice(out, func(i, j int) bool { return out[i].Digest < out[j].Digest })
+	return out
+}
+
+// The builder's tools over the toolchains it heard (design 47 G §604, §546).
+const (
+	ToolchainsTool     = "builder_toolchains"
+	ToolchainsDropTool = "builder_toolchains_drop"
+)
diff --git a/modules/mesh-delivery-builder/buildrun/toolchains_test.go b/modules/mesh-delivery-builder/buildrun/toolchains_test.go
index 72aeab92..82b78c5e 100644
--- a/modules/mesh-delivery-builder/buildrun/toolchains_test.go
+++ b/modules/mesh-delivery-builder/buildrun/toolchains_test.go
@@ -1,50 +1,49 @@
 package buildrun
 
 import (
+	"reflect"
 	"testing"
-	"time"
 
 	"git.novox.be/novox/mesh-delivery/sdk/buildstep"
 )
 
-func tcValue(t *testing.T, language, version string) []byte {
-	t.Helper()
-	now := time.Now()
-	b, err := buildstep.EncodeToolchain(buildstep.Toolchain{Language: language, Version: version, Recipe: "1", At: now})
-	if err != nil {
-		t.Fatal(err)
-	}
-	return b
+func tc(language, version, digest string) buildstep.Toolchain {
+	return buildstep.Toolchain{Language: language, Version: version, Recipe: "1", Digest: digest}
 }
 
-func TestToolchainSetKeepsEachNodesEntryByLanguageAndSaysWhenOneChanged(t *testing.T) { // 1607/AC6
+func TestToolchainSetKeepsEachNodesEntryByLanguageAndSaysWhenOneChanged(t *testing.T) { // 1607/AC6, design 47 G §604
 	var s ToolchainSet
-	if !s.Put(GoBuildModule, "novox.go", tcValue(t, "go", "go1.27.1"), false) {
+	if !s.Set("novox", tc("go", "go1.27.1", "sha256:a")) {
 		t.Error("a first entry did not count as a change")
 	}
-	if s.Put(GoBuildModule, "novox.go", tcValue(t, "go", "go1.27.1"), false) {
+	if s.Set("novox", tc("go", "go1.27.1", "sha256:a")) {
 		t.Error("the same entry again counted as a change")
 	}
-	s.Put(GoBuildModule, "ace.go", tcValue(t, "go", "go1.27.1"), false)
-	s.Put(NodeBuildModule, "ace.typescript", tcValue(t, "typescript", "tsc5"), false)
+	if !s.Set("novox", tc("go", "go1.27.1", "sha256:b")) {
+		t.Error("a new digest at one version did not count as a change")
+	}
+	s.Set("ace", tc("go", "go1.27.1", "sha256:b"))
+	s.Set("ace", tc("typescript", "tsc5", ""))
 	if got := s.Entries("go"); len(got) != 2 {
 		t.Errorf("go entries = %+v, want two", got)
 	}
 	if got := s.Entries("typescript"); len(got) != 1 || got[0].Node != "ace" || got[0].Version != "tsc5" {
 		t.Errorf("typescript entries = %+v", got)
 	}
-	if !s.Put(GoBuildModule, "ace.go", nil, true) || len(s.Entries("go")) != 1 {
-		t.Error("a delete did not remove the node's entry")
+	if !s.Delete("ace", "go") || len(s.Entries("go")) != 1 || s.Delete("ace", "go") {
+		t.Error("a delete did not remove the node's entry once")
 	}
-	// What is not a toolchain of the module's language is left out.
-	s = ToolchainSet{}
-	if s.Put(GoBuildModule, "novox.typescript", tcValue(t, "typescript", "x"), false) {
-		t.Error("a typescript toolchain in the go build module's bucket counted")
-	}
-	if s.Put(GoBuildModule, "novox.go", []byte("not json"), false) || s.Put("other-module", "novox.go", tcValue(t, "go", "x"), false) {
-		t.Error("garbage or an unknown module counted")
-	}
-	if len(s.Entries("go")) != 0 {
-		t.Error("an entry was kept")
+}
+
+// Design 47 G §472, §574: the digests are those the nodes reporting the agreed version report, sorted, with their nodes.
+func TestDigestsOfTheAgreedVersion(t *testing.T) {
+	entries := []buildstep.NodeToolchain{
+		{Node: "novox", Toolchain: tc("go", "1.26.0", "sha256:b")}, {Node: "ace", Toolchain: tc("go", "1.26.0", "sha256:a")},
+		{Node: "g14", Toolchain: tc("go", "1.26.0", "sha256:a")}, {Node: "shanks", Toolchain: tc("go", "1.25.0", "sha256:c")},
+		{Node: "old", Toolchain: tc("go", "1.26.0", "")}}
+	got := Digests(entries, tc("go", "1.26.0", ""))
+	want := []AgreedDigest{{Digest: "sha256:a", Nodes: []string{"ace", "g14"}}, {Digest: "sha256:b", Nodes: []string{"novox"}}}
+	if !reflect.DeepEqual(got, want) {
+		t.Errorf("digests = %+v, want %+v", got, want)
 	}
 }
diff --git a/modules/mesh-delivery-builder/cmd/mesh-delivery-builder-tools/main.go b/modules/mesh-delivery-builder/cmd/mesh-delivery-builder-tools/main.go
index bbd75eaf..7e201f0a 100644
--- a/modules/mesh-delivery-builder/cmd/mesh-delivery-builder-tools/main.go
+++ b/modules/mesh-delivery-builder/cmd/mesh-delivery-builder-tools/main.go
@@ -372,6 +372,7 @@ func main() {
 	}}
 	tools := Tools(r, put, askQueue(stdio.State(build.QueuesState), 25*time.Second), buildAgain, stdio.Log(builds.BuilderLog).Since, time.Now, vr, fr, ofr)
 	tools = append(tools, reservedTools(rr, buildAgain, time.Now, meshhandactsclient.Recorder{Ask: stdio.Ask})...)
+	tools = append(tools, toolchainsTools(stdio.State(buildrun.ToolchainsHeardState), meshhandactsclient.Recorder{Ask: stdio.Ask}, time.Now)...)
 	// The builder's expiring keys (state bounds): what each bounds and when it ends.
 	tools = append(tools, stdio.Tool{Name: versions.BoundsTool, Description: versions.BoundsDescription,
 		Input: map[string]any{"type": "object", "properties": map[string]any{}},
diff --git a/modules/mesh-delivery-builder/cmd/mesh-delivery-builder-tools/toolchains.go b/modules/mesh-delivery-builder/cmd/mesh-delivery-builder-tools/toolchains.go
new file mode 100644
index 00000000..06ec72b9
--- /dev/null
+++ b/modules/mesh-delivery-builder/cmd/mesh-delivery-builder-tools/toolchains.go
@@ -0,0 +1,82 @@
+package main
+
+import (
+	"fmt"
+	"sort"
+	"strings"
+	"time"
+
+	"git.novox.be/novox/mesh-contracts/health-and-repair/go/clients/meshhandactsclient"
+	"git.novox.be/novox/mesh-delivery/modules/mesh-delivery-builder/buildrun"
+	"git.novox.be/novox/mesh-delivery/sdk/buildstep"
+	stdio "git.novox.be/novox/mesh-sdk/go"
+)
+
+// heardState is the builder's state toolchains-heard as the tools bundle reads and deletes in it.
+type heardState interface {
+	Keys() ([]string, error)
+	Get(key string) (*stdio.StateEntry, error)
+	Delete(key string) error
+}
+
+// toolchainsTools are builder_toolchains, which lists the toolchains the builder heard from the build seats, and
+// builder_toolchains_drop, which deletes one key and writes it in the hand-act log (design 47 G §604, §546). The drop is
+// of class act, with the default callers: the bus refuses another caller.
+func toolchainsTools(st heardState, acts meshhandactsclient.Recorder, now func() time.Time) []stdio.Tool {
+	return []stdio.Tool{
+		{Name: buildrun.ToolchainsTool,
+			Description: "The toolchains the builder heard from the build seats' toolchain-reported, one key <node>.<language> each: its version, " +
+				"recipe, the digest of its toolchain program and when it was said. The builder agrees a language's version from these, and forgets a node's " +
+				"when the node-engine seat says the build module stopped there. Read-only.",
+			Input: map[string]any{"type": "object", "properties": map[string]any{}},
+			Run: func(map[string]any) (any, error) {
+				keys, err := st.Keys()
+				if err != nil {
+					return nil, err
+				}
+				sort.Strings(keys)
+				rows := []map[string]any{}
+				for _, k := range keys {
+					e, err := st.Get(k)
+					if err != nil || e == nil {
+						continue
+					}
+					row := map[string]any{"key": k}
+					if tc, err := buildstep.DecodeToolchain(e.Value); err != nil {
+						row["error"] = err.Error()
+					} else {
+						row["version"], row["recipe"], row["digest"], row["said"] = tc.Version, tc.Recipe, tc.Digest, tc.At
+					}
+					rows = append(rows, row)
+				}
+				return map[string]any{"toolchains": rows}, nil
+			}},
+		{Name: buildrun.ToolchainsDropTool,
+			Description: "Drop one node's toolchain of a language from what the builder heard, by hand: a build module that left a node and said nothing. " +
+				"The builder agrees without it; the node's build module says it again at its start and on each change. Written in the hand-act log (mesh-hand-acts).",
+			Input: map[string]any{"type": "object", "required": []string{"key", "why"}, "properties": map[string]any{
+				"key": map[string]any{"type": "string", "description": "<node>.<language>, as builder_toolchains lists it"},
+				"why": map[string]any{"type": "string", "description": "why, in plain words"}}},
+			Run: func(args map[string]any) (any, error) {
+				str := func(k string) string { s, _ := args[k].(string); return strings.TrimSpace(s) }
+				key, why := str("key"), str("why")
+				if _, _, err := buildstep.ParseToolchainKey(key); err != nil {
+					return nil, err
+				}
+				if why == "" {
+					return nil, fmt.Errorf("why is required")
+				}
+				if e, err := st.Get(key); err != nil || e == nil {
+					return nil, fmt.Errorf("%s holds no key %s", buildrun.ToolchainsHeardState, key)
+				}
+				if _, err := acts.Record(meshhandactsclient.Request{What: fmt.Sprintf("dropped the toolchain %s from what the builder heard", key),
+					Why: why, Cause: buildrun.ToolchainsDropTool, Verb: "toolchains-drop"}); err != nil {
+					return nil, fmt.Errorf("the hand act was not recorded through mesh-hand-acts, so nothing was dropped: %w", err)
+				}
+				if err := st.Delete(key); err != nil {
+					return nil, err
+				}
+				return map[string]any{"key": key, "dropped": true, "at": now().UTC()}, nil
+			}},
+	}
+}
diff --git a/modules/mesh-delivery-builder/cmd/mesh-delivery-builder-tools/toolchains_test.go b/modules/mesh-delivery-builder/cmd/mesh-delivery-builder-tools/toolchains_test.go
new file mode 100644
index 00000000..70429914
--- /dev/null
+++ b/modules/mesh-delivery-builder/cmd/mesh-delivery-builder-tools/toolchains_test.go
@@ -0,0 +1,73 @@
+package main
+
+import (
+	"encoding/json"
+	"strings"
+	"testing"
+	"time"
+
+	"git.novox.be/novox/mesh-contracts/health-and-repair/go/clients/meshhandactsclient"
+	"git.novox.be/novox/mesh-delivery/modules/mesh-delivery-builder/buildrun"
+	"git.novox.be/novox/mesh-delivery/sdk/buildstep"
+	stdio "git.novox.be/novox/mesh-sdk/go"
+)
+
+type fakeHeard struct{ m map[string]json.RawMessage }
+
+func (f *fakeHeard) Keys() ([]string, error) {
+	var out []string
+	for k := range f.m {
+		out = append(out, k)
+	}
+	return out, nil
+}
+func (f *fakeHeard) Get(k string) (*stdio.StateEntry, error) {
+	v, ok := f.m[k]
+	if !ok {
+		return nil, nil
+	}
+	return &stdio.StateEntry{Key: k, Value: v}, nil
+}
+func (f *fakeHeard) Delete(k string) error { delete(f.m, k); return nil }
+
+// Design 47 G §604, §546: builder_toolchains lists the keys; builder_toolchains_drop deletes one with its why, after the
+// hand act is recorded, and nothing is deleted when it is not.
+func TestToolchainsToolsListAndDropAKeyAfterTheHandAct(t *testing.T) {
+	data, err := buildstep.EncodeToolchain(buildstep.Toolchain{Language: "go", Version: "1.26.0", Recipe: "1", Digest: "sha256:a", At: time.Now()})
+	if err != nil {
+		t.Fatal(err)
+	}
+	st := &fakeHeard{m: map[string]json.RawMessage{"ace.go": data}}
+	asked := 0
+	var failAct error
+	acts := meshhandactsclient.Recorder{Ask: func(string, any) (json.RawMessage, error) {
+		asked++
+		return json.RawMessage(`{"id":"h1"}`), failAct
+	}}
+	tools := toolchainsTools(st, acts, time.Now)
+	run := func(name string, args map[string]any) (any, error) {
+		for _, tl := range tools {
+			if tl.Name == name {
+				return tl.Run(args)
+			}
+		}
+		t.Fatalf("no tool %s", name)
+		return nil, nil
+	}
+	got, err := run(buildrun.ToolchainsTool, nil)
+	rows := got.(map[string]any)["toolchains"].([]map[string]any)
+	if err != nil || len(rows) != 1 || rows[0]["key"] != "ace.go" || rows[0]["digest"] != "sha256:a" {
+		t.Fatalf("listed %v, %v", got, err)
+	}
+	if _, err := run(buildrun.ToolchainsDropTool, map[string]any{"key": "ace.go", "why": ""}); err == nil {
+		t.Fatal("a drop with no why was taken")
+	}
+	failAct = json.Unmarshal([]byte("x"), new(int))
+	if _, err := run(buildrun.ToolchainsDropTool, map[string]any{"key": "ace.go", "why": "ace left"}); err == nil || !strings.Contains(err.Error(), "nothing was dropped") || len(st.m) != 1 {
+		t.Fatalf("a hand act not recorded still dropped: %v", err)
+	}
+	failAct = nil
+	if _, err := run(buildrun.ToolchainsDropTool, map[string]any{"key": "ace.go", "why": "ace left"}); err != nil || len(st.m) != 0 || asked < 2 {
+		t.Fatalf("the drop: %v, keys left %d", err, len(st.m))
+	}
+}
diff --git a/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/gone_integration_test.go b/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/gone_integration_test.go
index ec0783ec..4c50f3ca 100644
--- a/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/gone_integration_test.go
+++ b/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/gone_integration_test.go
@@ -69,7 +69,7 @@ func eventsConsumer(t *testing.T, b *bed, node string) {
 		t.Fatal(err)
 	}
 	if _, err := b.js.CreateOrUpdateConsumer(b.ctx, eventsStream, jetstream.ConsumerConfig{Durable: node + "_mesh-delivery-builder",
-		AckPolicy: jetstream.AckExplicitPolicy, FilterSubjects: []string{sweep.SubjectArtifactsGone}}); err != nil {
+		AckPolicy: jetstream.AckExplicitPolicy, FilterSubjects: []string{sweep.SubjectArtifactsGone, "mesh.seat.node-build-go.event.toolchain-reported.*", "mesh.seat.node-build-node.event.toolchain-reported.*"}}); err != nil {
 		t.Fatal(err)
 	}
 }
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 c277bc6c..fbfc0f50 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
@@ -213,7 +213,7 @@ type bed struct {
 	candidates jetstream.KeyValue
 	source     jetstream.KeyValue
 	builds     jetstream.KeyValue
-	tools      map[string]jetstream.KeyValue
+	heard      jetstream.KeyValue // the state toolchains-heard
 	instances  jetstream.KeyValue
 	packages   jetstream.KeyValue // the indexer's packages, served by its read tool and views family
 	out        *saidLog           // the builder's process log, every instance's
@@ -265,21 +265,21 @@ func startBedWith(t *testing.T, closed bool) *bed {
 	}
 	ctx, cancel := context.WithTimeout(context.Background(), 90*time.Second)
 	t.Cleanup(cancel)
-	b := &bed{ctx: ctx, js: js, tools: map[string]jetstream.KeyValue{}, srvURL: srv.ClientURL(), dir: dir}
-	for module, stream := range toolchainStreams {
-		if _, err := js.CreateStream(ctx, jetstream.StreamConfig{Name: stream, Subjects: []string{"mesh.stream." + module + ".event.toolchain.reported"}}); err != nil {
+	b := &bed{ctx: ctx, js: js, srvURL: srv.ClientURL(), dir: dir}
+	// EVENTS, where the build seats say toolchain-reported (design 47 G §492), with each builder's durable consumer of it, and
+	// the builder's state toolchains-heard (§604).
+	if _, err := js.CreateOrUpdateStream(ctx, jetstream.StreamConfig{Name: eventsStream, Subjects: []string{"mesh.mod.*.event.>", "mesh.seat.*.event.>"}}); err != nil {
+		t.Fatal(err)
+	}
+	for _, node := range []string{"n1", "n2"} {
+		if _, err := js.CreateOrUpdateConsumer(ctx, eventsStream, jetstream.ConsumerConfig{Durable: node + "_mesh-delivery-builder", AckPolicy: jetstream.AckExplicitPolicy}); err != nil {
 			t.Fatal(err)
 		}
-		for _, node := range []string{"n1", "n2"} {
-			if _, err := js.CreateOrUpdateConsumer(ctx, stream, jetstream.ConsumerConfig{Durable: node + "_mesh-delivery-builder", AckPolicy: jetstream.AckExplicitPolicy}); err != nil {
-				t.Fatal(err)
-			}
-		}
-		kv, err := js.CreateKeyValue(ctx, jetstream.KeyValueConfig{Bucket: buildrun.ToolchainsBucket(module), History: 1})
-		if err != nil {
-			t.Fatal(err)
-		}
-		b.tools[module] = kv
+	}
+	if kv, err := js.CreateKeyValue(ctx, jetstream.KeyValueConfig{Bucket: buildrun.ToolchainsHeardBucket, History: 1}); err != nil {
+		t.Fatal(err)
+	} else {
+		b.heard = kv
 	}
 	mk := func(name string, history int) jetstream.KeyValue {
 		kv, err := js.CreateKeyValue(ctx, jetstream.KeyValueConfig{Bucket: name, History: uint8(history)})
@@ -344,18 +344,15 @@ func (b *bed) logged(t *testing.T, module string) []builds.BuildLogEntry {
 	return out
 }
 
-// report writes a node's toolchains key of a build module and says so on the module's stream, as the module does.
+// report says a node's toolchain of a language on the build module's seat, as the seat's holder does (design 47 G §492).
 func (b *bed) report(t *testing.T, module, node, language, version, recipe string) {
 	t.Helper()
-	data, err := sdkstep.EncodeToolchain(sdkstep.Toolchain{Language: language, Version: version, Recipe: recipe, At: time.Now().UTC()})
+	seat := map[string]string{"mesh-build-go": "node-build-go", "mesh-build-node": "node-build-node"}[module]
+	data, err := json.Marshal(map[string]string{"node": node, "language": language, "version": version, "recipe": recipe, "digest": "sha256:" + strings.Repeat("a", 64)})
 	if err != nil {
 		t.Fatal(err)
 	}
-	key, _ := sdkstep.ToolchainKey(node, language)
-	if _, err := b.tools[module].Put(b.ctx, key, data); err != nil {
-		t.Fatal(err)
-	}
-	if _, err := b.js.Publish(b.ctx, "mesh.stream."+module+".event.toolchain.reported", []byte(`{}`)); err != nil {
+	if _, err := b.js.Publish(b.ctx, "mesh.seat."+seat+".event.toolchain-reported."+node, data); err != nil {
 		t.Fatal(err)
 	}
 }
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 c04e2884..9a743179 100644
--- a/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/main.go
+++ b/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/main.go
@@ -31,6 +31,7 @@ import (
 
 	"git.novox.be/novox/mesh-delivery/contracts/go/clients/meshdeliveryclient"
 	sweep "git.novox.be/novox/mesh-delivery/contracts/go/seats/meshartifactsweep"
+	"git.novox.be/novox/mesh-delivery/contracts/go/seats/meshbuilds"
 	"git.novox.be/novox/mesh-delivery/contracts/go/seats/meshcatalog"
 	"git.novox.be/novox/mesh-delivery/modules/mesh-delivery-builder/builds"
 	"git.novox.be/novox/mesh-delivery/sdk/buildstep"
@@ -247,12 +248,27 @@ func run(ctx context.Context, getenv func(string) string, logOut io.Writer) erro
 			}
 		}()
 	}
-	// The toolchains first, so a build that starts from the first modules value finds the nodes.
-	watch := newToolchainWatch(ctx, js, tools, b.NodesChanged, logger)
-	// Only the toolchain reports of nodes the catalogue places the build module on count (issue 1940, ADR 0549 §3): the
-	// assignments is settled first, so the toolchains settle through the gate already knowing it.
-	gate := buildrun.NewToolchainGate([]string{buildrun.GoBuildModule, buildrun.NodeBuildModule}, tools.Put, logger.Printf)
-	watch.put = gate.Toolchain
+	// The toolchains the build seats say (design 47 G §492, §604): kept in the state toolchains-heard, read back at the start, so
+	// a build that starts from the first modules value finds the nodes; the assignments only counts the nodes (ADR 0624 §1).
+	gate := buildrun.NewPlacedNodes(logger.Printf)
+	heardTools := newToolchainsHeard(tools, b.NodesChanged, func(ctx context.Context, e meshbuilds.ToolchainAgreed) error {
+		return emitSeatEvent(context.WithoutCancel(ctx), js, cred, meshbuilds.SubjectToolchainAgreed, "toolchain-agreed-"+e.Language+"-"+e.Version, e)
+	}, logger)
+	process.AwaitBucket(ctx, js, conn, buildrun.ToolchainsHeardBucket, "the toolchains heard are kept in memory only, and builder_toolchains shows none", logger.Printf).
+		Ready(func(kv jetstream.KeyValue) {
+			heardTools.bind(ctx, kvHeard{kvKeeper{ctx: ctx, kv: kv}})
+			heardTools.readRunning(ctx, js)
+			dropped := func(e jetstream.KeyValueEntry) {
+				if !opOf(e) {
+					heardTools.Dropped(ctx, e.Key())
+				}
+			}
+			if w, err := kv.WatchAll(ctx, jetstream.UpdatesOnly()); err != nil {
+				process.NotWatched(logger.Printf, buildrun.ToolchainsHeardBucket, err, "builder_toolchains_drop is not heard until the builder starts again")
+			} else {
+				go func() { errs <- follow(ctx, w, dropped) }()
+			}
+		})
 	// What each counted node's engine reads (ADR 0618 §2, ADR 0624 §1): asked through the node-engine seat's verb as the
 	// builder's own account, for every node the assignments names, and kept in the state engine-reads once it is bound.
 	reads := newEngineReads(calls.CallKeptOn, gate, logger.Printf)
@@ -284,7 +300,7 @@ func run(ctx context.Context, getenv func(string) string, logOut io.Writer) erro
 	// asked when the bound ends), is call-unanswered in the builder's findings (issue 1966, ADR 0668 §3, ADR 0596 §2).
 	reads.callsOf(found, pubBoundsKV.KV, heardBy(calls.CallKept), logger.Printf)
 	b.Forms = reads.built
-	// Until the assignments's first view is answered the gate passes every report on, as before the assignments is settled.
+	// The assignments names the nodes the builder counts, once its first view is answered.
 	assignmentsErrs := make(chan error, 1)
 	go func() {
 		select {
@@ -299,12 +315,6 @@ func run(ctx context.Context, getenv func(string) string, logOut io.Writer) erro
 		}
 		assignmentsErrs <- <-pe
 	}()
-	if err := watch.start(); err != nil {
-		return err
-	}
-	// A build module says each time it wrote its toolchains key: its stream, and the builder's durable consumer on it, are
-	// made by the controller. Where the stream is not there yet the builder says so and is started again with the build
-	// module.
 	// Each consumer that is not there yet is the finding family-not-heard naming its stream until it binds at a later
 	// start (heard.Writer; ADR 0615 §5); one there that cannot be heard stops the builder, as before.
 	notHeard := found.notHeard(ctx)
@@ -324,9 +334,6 @@ func run(ctx context.Context, getenv func(string) string, logOut io.Writer) erro
 			return nil
 		})
 	}
-	for _, module := range []string{buildrun.GoBuildModule, buildrun.NodeBuildModule} {
-		hear(toolchainStreams[module], module+"'s toolchain reports are not heard until the builder starts again", func(m jetstream.Msg) { watch.Reported(m) })
-	}
 	// The seat mesh-artifact-sweep says artifacts-gone when it found a key's blob gone (issue 1937, ADR 0571 §2): the
 	// builder's durable consumer on EVENTS, made by the grants part from the manifest's consumes. Where it is not there yet the builder says
 	// so; it still asks held at its start and at every module value.
@@ -336,7 +343,7 @@ func run(ctx context.Context, getenv func(string) string, logOut io.Writer) erro
 	// And the four registry seats' published, refused and removed (DLV-B4), which move a numbered version.
 	seats := seatHearer{n: numberer, b: b, logf: logger.Printf, pub: pubs, res: reserved}
 	events := func(m jetstream.Msg) {
-		if reads.heard(m, logger.Printf) || floor.heard(ctx, m) || reserved.heard(ctx, m) || seats.heard(ctx, m) { // reads: the node-engine seat's manifest-reads-changed (ADR 0618 §4)
+		if reads.heard(m, logger.Printf) || heardTools.Reported(ctx, m) || heardTools.Running(ctx, m) || floor.heard(ctx, m) || reserved.heard(ctx, m) || seats.heard(ctx, m) { // reads: the node-engine seat's manifest-reads-changed (ADR 0618 §4)
 			return
 		}
 		heardGone(ctx, b, m, logger.Printf)
@@ -430,8 +437,6 @@ func run(ctx context.Context, getenv func(string) string, logOut io.Writer) erro
 		return err
 	case err := <-assignmentsErrs:
 		return err
-	case err := <-watch.errs:
-		return err
 	}
 }
 
diff --git a/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/names_test.go b/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/names_test.go
index 6b3b86c3..2c1549b5 100644
--- a/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/names_test.go
+++ b/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/names_test.go
@@ -26,7 +26,7 @@ func TestTheNamesAreTheManifests(t *testing.T) {
 	}
 	for _, read := range []string{
 		gateModule + ".source",
-		"mesh-build-go.steps", "mesh-build-go.toolchains", "mesh-build-image.steps", "mesh-build-node.steps", "mesh-build-node.toolchains",
+		"mesh-build-go.steps", "mesh-build-image.steps", "mesh-build-node.steps",
 	} {
 		if !slices.Contains(m.Reads, read) {
 			t.Errorf("the builder reads %s, its manifest's reads are %v", read, m.Reads)
@@ -40,7 +40,7 @@ func TestTheNamesAreTheManifests(t *testing.T) {
 	}
 	for want, got := range map[string]string{
 		"mesh-delivery-gate_source": sourceBucket, "mesh-build-go_steps": buildrun.StepsBucket("mesh-build-go"),
-		"mesh-build-node_toolchains": buildrun.ToolchainsBucket("mesh-build-node"), "mesh-delivery-indexer_packages": packagesBucket,
+		buildrun.ToolchainsHeardBucket: "mesh-delivery-builder_toolchains-heard", "mesh-delivery-indexer_packages": packagesBucket,
 		"mesh-delivery-assigner_assignments": buildrun.AssignmentsBucket,
 	} {
 		if want != got {
diff --git a/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/reads.go b/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/reads.go
index 1cc99503..cd9a1702 100644
--- a/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/reads.go
+++ b/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/reads.go
@@ -28,7 +28,7 @@ const engineReadsBucket = builds.BuilderModule + "_" + EngineReadsState
 // engineReads keeps the statements and the counted nodes for the builder's forms (build.Builder.Forms).
 type engineReads struct {
 	keeper  *enginereads.Keeper
-	gate    *buildrun.ToolchainGate
+	gate    *buildrun.PlacedNodes
 	mu      sync.Mutex
 	counted []string
 	// window is the old reference form's window over these statements (DLV-B9); nil keeps none.
@@ -39,7 +39,7 @@ type engineReads struct {
 }
 
 // newEngineReads asks through call (process.Conn.CallKeptOn, a kept call; ADR 0668) and keeps each answer in the state once it is bound.
-func newEngineReads(call enginereads.Caller, gate *buildrun.ToolchainGate, logf func(string, ...any)) *engineReads {
+func newEngineReads(call enginereads.Caller, gate *buildrun.PlacedNodes, logf func(string, ...any)) *engineReads {
 	r := &engineReads{gate: gate, keeper: &enginereads.Keeper{Call: call, Logf: logf}}
 	r.keeper.Changed = func() {
 		r.stepWindow()
diff --git a/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/refused_test.go b/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/refused_test.go
index d3d4bf22..cafc3e8a 100644
--- a/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/refused_test.go
+++ b/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/refused_test.go
@@ -34,24 +34,16 @@ import (
 	"mesh-delivery-builder/internal/versions"
 )
 
-// 1945 (a part exits at start for a bucket it works without): a bus that refuses every toolchains bucket leaves the
-// watch unstarted and the part running, said; a refused bucket it cannot work without is an error naming the bucket and
-// its grant. The gate over the seat's assignments, and its refusal, are mesh-sdk's (buildrun.ToolchainGate,
+// 1945 (a part exits at start for a bucket it works without): a refused bucket it cannot work without is an error naming the bucket and
+// its grant. The gate over the seat's assignments, and its refusal, are mesh-sdk's (buildrun.PlacedNodes,
 // issue 774).
 func TestARefusedBucketIsSaidAndThePartGoesOn(t *testing.T) {
 	t.Run("a floor's wake is heard on the events consumer (design 51 The floor)", aFloorsWakeIsHeard)
 	t.Run("a failed trunk build is a finding until a later done one (DLV-B7)", aFailedTrunkBuildIsAFinding)
 	t.Run("a branch's end is acknowledged once its tagged versions are removed (design 51 Tagged versions)", aBranchsEndIsHeard)
-	set := &buildrun.ToolchainSet{}
 	var logs bytes.Buffer
 	logger := log.New(&logs, "", 0)
-	refused := refusingBus{err: errors.New("nats: permissions violation for publish to $JS.API.CONSUMER.CREATE.KV_mesh-build-node_toolchains")}
-	if err := newToolchainWatch(context.Background(), refusingBus{refuseOpen: true, err: refused.err}, set, func(context.Context) {}, logger).start(); err != nil {
-		t.Errorf("a refused toolchains bucket stopped the start: %v", err)
-	}
-	if !strings.Contains(logs.String(), "cannot be read") {
-		t.Errorf("the refusals were not said: %q", logs.String())
-	}
+	refused := refusingBus{err: errors.New("nats: permissions violation for publish to $JS.API.CONSUMER.CREATE.KV_mesh-delivery-indexer_modules")}
 	if _, err := process.EssentialBucket(context.Background(), refusingBus{refuseOpen: true, err: refused.err}, "builder", "mesh-delivery-indexer_modules", "work"); err == nil ||
 		!strings.Contains(err.Error(), "grant of mesh-delivery-indexer_modules") {
 		t.Errorf("a refused bucket the part needs: %v, want an error naming its grant", err)
@@ -74,7 +66,7 @@ func TestARefusedBucketIsSaidAndThePartGoesOn(t *testing.T) {
 // away node keeps its last statement; a node the assignments no longer names leaves the count, its key removed; and
 // builder_engine_reads drops one node's key.
 func theCountedNodesEngineReads(t *testing.T) {
-	gate := buildrun.NewToolchainGate(nil, func(string, string, []byte, bool) bool { return false }, t.Logf)
+	gate := buildrun.NewPlacedNodes(t.Logf)
 	place := func(nodes ...string) {
 		for _, node := range []string{"n1", "n2"} {
 			pl := meshmoduleassigner.Assignments{Node: node}
diff --git a/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/toolchains.go b/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/toolchains.go
index 82734a16..62c88a80 100644
--- a/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/toolchains.go
+++ b/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/toolchains.go
@@ -2,107 +2,290 @@ package main
 
 import (
 	"context"
+	"encoding/json"
 	"errors"
 	"fmt"
 	"log"
 	"strings"
 	"sync"
-
-	"git.novox.be/novox/mesh-delivery/modules/mesh-delivery-builder/buildrun"
-	"git.novox.be/novox/mesh-sdk/go/process"
+	"time"
 
 	"github.com/nats-io/nats.go/jetstream"
+
+	"git.novox.be/novox/mesh-contracts/go/seats/nodeengine"
+	"git.novox.be/novox/mesh-delivery/contracts/go/seats/meshbuilds"
+	"git.novox.be/novox/mesh-delivery/contracts/go/seats/nodebuildgo"
+	"git.novox.be/novox/mesh-delivery/contracts/go/seats/nodebuildnode"
+	"git.novox.be/novox/mesh-delivery/modules/mesh-delivery-builder/buildrun"
+	"git.novox.be/novox/mesh-delivery/sdk/buildstep"
 )
 
-// toolchainStreams are the stream each build module carries its toolchain.reported event on, as the bus names it
-// (declared by the build modules, heard by this module through consumes).
-var toolchainStreams = map[string]string{buildrun.GoBuildModule: "TOOLCHAINS_GO", buildrun.NodeBuildModule: "TOOLCHAINS_NODE"}
-
-// toolchainWatch keeps the build modules' toolchains in a buildrun.ToolchainSet and tells the builder when one changed. A
-// build module's bucket is made when it is assigned, after the builder started, and the builder holds no timer (ADR 0437
-// §8): it watches the buckets that exist at start, and a build module says each time it wrote its toolchains key
-// (toolchain.reported, handled by Reported); a bucket not watched yet is then watched.
-type toolchainWatch struct {
-	ctx context.Context
-	js  bucketOpener
-	set *buildrun.ToolchainSet
-	// put takes a change of a toolchains bucket in: set.Put, or the gate of the assigned build nodes before it (issue 1940).
-	put     func(module, key string, value []byte, deleted bool) bool
-	changed func(ctx context.Context) // a language's entries changed: the failed builds are tried again
-	logger  *log.Logger
-	errs    chan error
-	mu      sync.Mutex
-	watched map[string]bool
+// toolchainReportedPrefixes are the subjects the three build seats say toolchain-reported on, a node its last token (design
+// 47 G §492). The builder hears them through the consumer of its manifest's consumes, and keeps what it heard in its
+// state toolchains-heard (§604).
+var toolchainReportedPrefixes = []string{
+	strings.TrimSuffix(nodebuildgo.SubjectToolchainReportedAll, "*"),
+	strings.TrimSuffix(nodebuildnode.SubjectToolchainReportedAll, "*"),
 }
 
-func newToolchainWatch(ctx context.Context, js bucketOpener, set *buildrun.ToolchainSet, changed func(context.Context), logger *log.Logger) *toolchainWatch {
-	return &toolchainWatch{ctx: ctx, js: js, set: set, put: set.Put, changed: changed, logger: logger, errs: make(chan error, len(buildrun.LanguageOf)), watched: map[string]bool{}}
+// heardKept is the state toolchains-heard: one key <node>.<language> (design 47 G §604).
+type heardKept interface {
+	Put(key string, value []byte) error
+	Delete(key string) error
 }
 
-// start watches the buckets that exist now; a missing one is said and waits for its build module's event.
-func (w *toolchainWatch) start() error {
-	for module := range buildrun.LanguageOf {
-		if err := w.ensure(module); err != nil {
-			return err
+// heardState is the state as the builder reads it back at its start.
+type heardState interface {
+	heardKept
+	Keys() ([]string, error)
+	Get(key string) ([]byte, error)
+}
+
+// kvHeard is heardState over the bound bucket.
+type kvHeard struct {
+	kvKeeper
+}
+
+func (k kvHeard) Keys() ([]string, error) {
+	keys, err := k.kv.Keys(k.ctx)
+	if errors.Is(err, jetstream.ErrNoKeysFound) {
+		return nil, nil
+	}
+	return keys, err
+}
+
+func (k kvHeard) Get(key string) ([]byte, error) {
+	e, err := k.kv.Get(k.ctx, key)
+	if err != nil {
+		return nil, err
+	}
+	return e.Value(), nil
+}
+
+// toolchainsHeard keeps the toolchains the build seats said (design 47 G §492, §604), forgets a node's on the node-engine
+// seat's stopped (§546), and says toolchain-agreed with its digests when a language's agreed version changes (§472, §574).
+type toolchainsHeard struct {
+	set     *buildrun.ToolchainSet
+	changed func(context.Context)
+	say     func(ctx context.Context, e meshbuilds.ToolchainAgreed) error
+	now     func() time.Time
+	logf    func(string, ...any)
+
+	mu     sync.Mutex
+	kept   heardKept            // nil until the state is bound: what was heard is kept in memory only, and written then
+	agreed map[string]string    // language -> the version last said
+	runAt  map[string]time.Time // <node>.<module> -> the `at` of the newest running read
+}
+
+func newToolchainsHeard(set *buildrun.ToolchainSet, changed func(context.Context), say func(context.Context, meshbuilds.ToolchainAgreed) error, logger *log.Logger) *toolchainsHeard {
+	return &toolchainsHeard{set: set, changed: changed, say: say, now: time.Now, logf: logger.Printf, agreed: map[string]string{}, runAt: map[string]time.Time{}}
+}
+
+// bind takes the bound state in: the toolchains it holds are read back (a restart needs no node to report again), and
+// what was heard before it was bound is written.
+func (h *toolchainsHeard) bind(ctx context.Context, state heardState) {
+	keys, err := state.Keys()
+	if err != nil {
+		h.logf("%s cannot be read, so the toolchains of before this start are not known: %v", buildrun.ToolchainsHeardState, err)
+	}
+	for _, k := range keys {
+		value, err := state.Get(k)
+		if err != nil {
+			continue
+		}
+		node, language, err := buildstep.ParseToolchainKey(k)
+		tc, derr := buildstep.DecodeToolchain(value)
+		if err != nil || derr != nil || tc.Language != language {
+			h.logf("%s.%s holds what is not a toolchain, and is left: %v %v", buildrun.ToolchainsHeardState, k, err, derr)
+			continue
+		}
+		h.set.Set(node, tc)
+	}
+	h.mu.Lock()
+	h.kept = state
+	h.mu.Unlock()
+	for _, language := range buildrun.LanguageOf {
+		for _, e := range h.set.Entries(language) {
+			h.keep(e.Node, e.Toolchain)
 		}
 	}
-	return nil
+	h.agree(ctx)
+	h.changed(ctx)
 }
 
-func (w *toolchainWatch) ensure(module string) error {
-	w.mu.Lock()
-	defer w.mu.Unlock()
-	if w.watched[module] {
-		return nil
+func (h *toolchainsHeard) keep(node string, tc buildstep.Toolchain) {
+	h.mu.Lock()
+	kept := h.kept
+	h.mu.Unlock()
+	if kept == nil {
+		return
 	}
-	name := buildrun.ToolchainsBucket(module)
-	kv, err := w.js.KeyValue(w.ctx, name)
-	switch {
-	case errors.Is(err, jetstream.ErrBucketNotFound):
-		w.logger.Printf("the bucket %s does not exist yet: it is watched when %s reports a toolchain", name, module)
-		return nil
-	case err != nil:
-		// Refused or not answered (its grant not on the bus yet, issue 1945): said, and opened again at the module's next report.
-		w.logger.Printf("the bucket %s cannot be read (%v): %s's toolchains are not heard until its next report", name, err, module)
-		return nil
-	}
-	watcher, err := settle(w.ctx, kv, func(e jetstream.KeyValueEntry) { w.put(module, e.Key(), e.Value(), !opOf(e)) })
+	key, err := buildstep.ToolchainKey(node, tc.Language)
 	if err != nil {
-		process.NotWatched(w.logger.Printf, name, err, fmt.Sprintf("%s's toolchains are not heard until its next report", module))
-		return nil
-	}
-	w.watched[module] = true
-	go func() {
-		w.errs <- follow(w.ctx, watcher, func(e jetstream.KeyValueEntry) {
-			if w.put(module, e.Key(), e.Value(), !opOf(e)) {
-				w.changed(w.ctx)
-			}
-		})
-	}()
-	w.changed(w.ctx) // what the settle read is new to the builder
-	return nil
-}
-
-// delivered is the part of a JetStream message the watch uses.
-type delivered interface {
-	Subject() string
-	Ack() error
-	Term() error
-}
-
-// Reported takes one toolchain.reported event of a build module in: the module is read off the subject,
-// mesh.stream.<module>.event.toolchain.reported, and its bucket is watched if it is not. A subject of no build module is
-// terminated; a failure stays unacknowledged, and the server delivers it again.
-func (w *toolchainWatch) Reported(m delivered) {
-	module, _, _ := strings.Cut(strings.TrimPrefix(m.Subject(), "mesh.stream."), ".event.")
-	if _, known := buildrun.LanguageOf[module]; !known || !strings.HasPrefix(m.Subject(), "mesh.stream.") {
-		w.logger.Printf("%s: not a build module's event, dropped", m.Subject())
-		_ = m.Term()
 		return
 	}
-	if err := w.ensure(module); err != nil {
-		w.logger.Printf("%s: left for redelivery: %v", m.Subject(), err)
-		return
+	data, err := buildstep.EncodeToolchain(tc)
+	if err == nil {
+		err = kept.Put(key, data)
+	}
+	if err != nil {
+		h.logf("%s.%s could not be written, so it is kept in memory only: %v", buildrun.ToolchainsHeardState, key, err)
+	}
+}
+
+// Reported takes one toolchain-reported of a build seat in; it answers whether the message was one. The toolchain is
+// kept in the state, and builds that waited for the nodes to agree are looked at again.
+func (h *toolchainsHeard) Reported(ctx context.Context, m jetstream.Msg) bool {
+	subject := m.Subject()
+	var prefix string
+	for _, p := range toolchainReportedPrefixes {
+		if strings.HasPrefix(subject, p) {
+			prefix = p
+		}
+	}
+	if prefix == "" {
+		return false
 	}
 	_ = m.Ack()
+	var e nodebuildgo.ToolchainReported
+	if err := json.Unmarshal(m.Data(), &e); err != nil || e.Node == "" || e.Node != strings.TrimPrefix(subject, prefix) {
+		h.logf("%s holds no toolchain of its node, and is dropped: %v", subject, err)
+		return true
+	}
+	tc := buildstep.Toolchain{Language: e.Language, Version: e.Version, Recipe: e.Recipe, Digest: e.Digest, At: h.now().UTC()}
+	if _, err := buildstep.EncodeToolchain(tc); err != nil {
+		h.logf("%s is no toolchain, and is dropped: %v", subject, err)
+		return true
+	}
+	if h.set.Set(e.Node, tc) {
+		h.keep(e.Node, tc)
+		h.agree(ctx)
+		h.changed(ctx)
+	}
+	return true
+}
+
+// Running takes one running of the node-engine seat in (design 47 G §546); it answers whether the message was one. A
+// running with no fingerprint is stopped (§365): the key <node>.<language> of the build module of that language on that
+// node is deleted. An event older by `at` than one taken before it changes nothing.
+func (h *toolchainsHeard) Running(ctx context.Context, m jetstream.Msg) bool {
+	if !strings.HasPrefix(m.Subject(), strings.TrimSuffix(nodeengine.SubjectRunningAll, "*.*")) {
+		return false
+	}
+	_ = m.Ack()
+	h.running(ctx, m.Data())
+	return true
+}
+
+func (h *toolchainsHeard) running(ctx context.Context, data []byte) {
+	var r nodeengine.Running
+	if err := json.Unmarshal(data, &r); err != nil {
+		h.logf("a running that does not read is dropped: %v", err)
+		return
+	}
+	id := r.Node + "." + r.Module
+	h.mu.Lock()
+	if prev, ok := h.runAt[id]; ok && r.At.Before(prev) {
+		h.mu.Unlock()
+		return
+	}
+	h.runAt[id] = r.At
+	kept := h.kept
+	h.mu.Unlock()
+	language, build := buildrun.LanguageOf[r.Module]
+	if !build || r.Fingerprint != "" {
+		return
+	}
+	if !h.set.Delete(r.Node, language) {
+		return
+	}
+	key, _ := buildstep.ToolchainKey(r.Node, language)
+	if kept != nil {
+		if err := kept.Delete(key); err != nil {
+			h.logf("%s.%s could not be deleted: %v", buildrun.ToolchainsHeardState, key, err)
+		}
+	}
+	h.agree(ctx)
+	h.changed(ctx)
+}
+
+// Dropped is the key's drop by a person (builder_toolchains_drop), taken from the state's watch.
+func (h *toolchainsHeard) Dropped(ctx context.Context, key string) {
+	node, language, err := buildstep.ParseToolchainKey(key)
+	if err != nil {
+		return
+	}
+	if h.set.Delete(node, language) {
+		h.agree(ctx)
+		h.changed(ctx)
+	}
+}
+
+// agree says toolchain-agreed for each language whose agreed version is not the one last said (design 47 G §472: said
+// only when the agreed version changes, ADR 0584 §1).
+func (h *toolchainsHeard) agree(ctx context.Context) {
+	for _, language := range buildrun.LanguageOf {
+		entries := h.set.Entries(language)
+		tc, none := buildstep.AgreedToolchain(entries)
+		if none != "" {
+			continue
+		}
+		h.mu.Lock()
+		same := h.agreed[language] == tc.Version
+		if !same {
+			h.agreed[language] = tc.Version
+		}
+		h.mu.Unlock()
+		if same {
+			continue
+		}
+		at := h.now().UTC()
+		e := meshbuilds.ToolchainAgreed{V: 1, At: &at, Language: language, Version: tc.Version, Digests: []meshbuilds.ToolchainAgreedDigestsItem{}}
+		for _, d := range buildrun.Digests(entries, tc) {
+			e.Digests = append(e.Digests, meshbuilds.ToolchainAgreedDigestsItem{Digest: d.Digest, Nodes: d.Nodes})
+		}
+		if err := h.say(ctx, e); err != nil {
+			h.logf("saying %s of %s %s: %v", meshbuilds.EventToolchainAgreed, language, tc.Version, err)
+			h.mu.Lock()
+			delete(h.agreed, language) // said again at the next change
+			h.mu.Unlock()
+		}
+	}
+}
+
+// lastPerSubject reads the last message of every subject of a stream kept last per subject, through an ordered consumer
+// made for that read (design 47 G §556), and hands each to each; it answers when the last of them was handed.
+func lastPerSubject(ctx context.Context, js jetstream.JetStream, stream, filter string, each func(subject string, data []byte)) error {
+	cons, err := js.OrderedConsumer(ctx, stream, jetstream.OrderedConsumerConfig{FilterSubjects: []string{filter}, DeliverPolicy: jetstream.DeliverLastPerSubjectPolicy})
+	if err != nil {
+		return fmt.Errorf("reading %s: %w", stream, err)
+	}
+	info, err := cons.Info(ctx)
+	if err != nil {
+		return fmt.Errorf("reading %s: %w", stream, err)
+	}
+	pending := int(info.NumPending)
+	if pending == 0 {
+		return nil
+	}
+	msgs, err := cons.Messages()
+	if err != nil {
+		return fmt.Errorf("reading %s: %w", stream, err)
+	}
+	defer msgs.Stop()
+	for ; pending > 0; pending-- {
+		m, err := msgs.Next()
+		if err != nil {
+			return fmt.Errorf("reading %s: %w", stream, err)
+		}
+		each(m.Subject(), m.Data())
+	}
+	return nil
+}
+
+// readRunning is the start's read of every node's module's last running (§556), before the consumer's.
+func (h *toolchainsHeard) readRunning(ctx context.Context, js jetstream.JetStream) {
+	if err := lastPerSubject(ctx, js, nodeengine.StreamRunning, nodeengine.SubjectRunningAll, func(_ string, data []byte) { h.running(ctx, data) }); err != nil {
+		h.logf("the running of the node-engine seat is not read at the start, so a build module stopped while this builder was away is forgotten at its next running: %v", err)
+	}
 }
diff --git a/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/toolchains_test.go b/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/toolchains_test.go
new file mode 100644
index 00000000..8018670c
--- /dev/null
+++ b/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/toolchains_test.go
@@ -0,0 +1,153 @@
+package main
+
+import (
+	"context"
+	"encoding/json"
+	"io"
+	"log"
+	"sort"
+	"sync"
+	"testing"
+	"time"
+
+	"github.com/nats-io/nats.go/jetstream"
+
+	"git.novox.be/novox/mesh-contracts/go/seats/nodeengine"
+	"git.novox.be/novox/mesh-delivery/contracts/go/seats/meshbuilds"
+	"git.novox.be/novox/mesh-delivery/modules/mesh-delivery-builder/buildrun"
+)
+
+// memState is the state toolchains-heard in memory.
+type memState struct {
+	mu sync.Mutex
+	m  map[string][]byte
+}
+
+func (s *memState) Put(k string, v []byte) error {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	if s.m == nil {
+		s.m = map[string][]byte{}
+	}
+	s.m[k] = v
+	return nil
+}
+func (s *memState) Delete(k string) error {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	delete(s.m, k)
+	return nil
+}
+func (s *memState) Get(k string) ([]byte, error) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	return s.m[k], nil
+}
+func (s *memState) Keys() ([]string, error) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	var out []string
+	for k := range s.m {
+		out = append(out, k)
+	}
+	sort.Strings(out)
+	return out, nil
+}
+
+// msg is a delivered message as the builder's consumer hands it.
+type msg struct {
+	jetstream.Msg
+	subject string
+	data    []byte
+}
+
+func (m msg) Subject() string { return m.subject }
+func (m msg) Data() []byte    { return m.data }
+func (m msg) Ack() error      { return nil }
+
+type heardRig struct {
+	h       *toolchainsHeard
+	state   *memState
+	said    []meshbuilds.ToolchainAgreed
+	changed int
+}
+
+func newHeardRig(t *testing.T, state *memState) *heardRig {
+	t.Helper()
+	r := &heardRig{state: state}
+	r.h = newToolchainsHeard(&buildrun.ToolchainSet{}, func(context.Context) { r.changed++ },
+		func(_ context.Context, e meshbuilds.ToolchainAgreed) error { r.said = append(r.said, e); return nil }, log.New(io.Discard, "", 0))
+	r.h.bind(context.Background(), state)
+	return r
+}
+
+func (r *heardRig) report(t *testing.T, seat, node, language, version, digest string) {
+	t.Helper()
+	data, _ := json.Marshal(map[string]string{"node": node, "language": language, "version": version, "recipe": "1", "digest": digest})
+	if !r.h.Reported(context.Background(), msg{subject: "mesh.seat." + seat + ".event.toolchain-reported." + node, data: data}) {
+		t.Fatal("a toolchain-reported was not taken")
+	}
+}
+
+func (r *heardRig) running(t *testing.T, node, module, fingerprint string, at time.Time) {
+	t.Helper()
+	data, _ := json.Marshal(nodeengine.Running{Node: node, Module: module, Fingerprint: fingerprint, At: at})
+	if !r.h.Running(context.Background(), msg{subject: nodeengine.SubjectRunning(node, module), data: data}) {
+		t.Fatal("a running was not taken")
+	}
+}
+
+// Design 47 G §492, §604, §472, §574, §546: the builder agrees from the toolchain-reported it heard, keeps them in
+// toolchains-heard, says toolchain-agreed with the digests only when the agreed version changes, and forgets a node's on
+// the node-engine seat's stopped.
+func TestTheBuilderKeepsTheToolchainsItHeardAndForgetsThemOnStopped(t *testing.T) {
+	da, db := "sha256:a", "sha256:b"
+	state := &memState{}
+	r := newHeardRig(t, state)
+	r.report(t, "node-build-go", "ace", "go", "1.26.0", da)
+	r.report(t, "node-build-go", "g14", "go", "1.26.0", da)
+	r.report(t, "node-build-go", "novox", "go", "1.26.0", db)
+	keys, _ := state.Keys()
+	if len(keys) != 3 || keys[0] != "ace.go" {
+		t.Fatalf("the state holds %v, want the three nodes' keys <node>.go", keys)
+	}
+	if len(r.said) != 1 || r.said[0].Version != "1.26.0" || r.said[0].Language != "go" {
+		t.Fatalf("toolchain-agreed said %+v, want one for go 1.26.0 (said only when the version changes)", r.said)
+	}
+	// The first report agreed it with one digest; a later digest of the same version is not said again.
+	if len(r.said[0].Digests) != 1 {
+		t.Fatalf("the first agreement carried %+v", r.said[0].Digests)
+	}
+	// A restarted builder reads the keys back and agrees the same version with no new report; the digests it says are all three nodes'.
+	again := newHeardRig(t, state)
+	if len(again.said) != 1 || again.said[0].Version != "1.26.0" || len(again.said[0].Digests) != 2 || again.said[0].Digests[0].Nodes[1] != "g14" {
+		t.Fatalf("a restarted builder said %+v, want go 1.26.0 with the digests of its three nodes", again.said)
+	}
+	// A version change is said; the stopped build module of ace takes ace's key out, a placement taking nothing.
+	again.report(t, "node-build-go", "ace", "go", "1.27.0", da)
+	again.report(t, "node-build-go", "g14", "go", "1.27.0", da)
+	if len(again.said) != 2 || again.said[1].Version != "1.27.0" {
+		t.Fatalf("a changed agreed version was not said: %+v", again.said)
+	}
+	at := time.Now()
+	again.running(t, "ace", buildrun.GoBuildModule, "src2:x", at) // running: nothing is forgotten
+	if k, _ := state.Keys(); len(k) != 3 {
+		t.Fatalf("a running forgot a key: %v", k)
+	}
+	again.running(t, "ace", buildrun.GoBuildModule, "", at.Add(time.Second)) // stopped: no fingerprint
+	if k, _ := state.Keys(); len(k) != 2 || k[0] != "g14.go" {
+		t.Fatalf("stopped on ace left %v, want g14.go and novox.go", k)
+	}
+	// An older running read after (the start's read of the stream kept last per subject) changes nothing.
+	before := again.changed
+	again.running(t, "g14", buildrun.GoBuildModule, "", at)
+	again.running(t, "g14", buildrun.GoBuildModule, "src2:y", at.Add(-time.Hour))
+	if k, _ := state.Keys(); len(k) != 1 || k[0] != "novox.go" || again.changed != before+1 {
+		t.Fatalf("after g14 stopped and an older running: %v", k)
+	}
+	// A key dropped by a person leaves the set.
+	again.h.Dropped(context.Background(), "novox.go")
+	if len(again.h.set.Entries("go")) != 0 {
+		t.Fatal("a dropped key stayed in the set")
+	}
+}
diff --git a/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/versions.go b/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/versions.go
index fbe610ac..ed1460ab 100644
--- a/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/versions.go
+++ b/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/versions.go
@@ -227,6 +227,25 @@ func emitEvent(ctx context.Context, js jetstream.JetStream, cred process.Account
 	return err
 }
 
+// emitSeatEvent says an event of a seat the builder holds, on the seat's subject (mesh.seat.<seat>.event.<event>).
+func emitSeatEvent(ctx context.Context, js jetstream.JetStream, cred process.Account, subject, id string, body any) error {
+	data, err := json.Marshal(body)
+	if err != nil {
+		return err
+	}
+	msg := nats.NewMsg(subject)
+	msg.Header.Set("x-event-id", id)
+	msg.Header.Set("x-source", cred.Module)
+	msg.Header.Set("x-node", cred.Node)
+	msg.Header.Set("x-time", time.Now().UTC().Format(time.RFC3339Nano))
+	msg.Header.Set("content-type", "application/json")
+	msg.Data = data
+	pub, cancel := context.WithTimeout(ctx, 10*time.Second)
+	defer cancel()
+	_, err = js.PublishMsg(pub, msg, jetstream.WithMsgID(id))
+	return err
+}
+
 // The events on the builder's consumer of EVENTS that wake a floor (design 51 *The floor*, DLV-B3b).
 var (
 	manifestAcceptedSubject = meshcatalog.SubjectManifestAccepted
diff --git a/modules/mesh-delivery-builder/go.mod b/modules/mesh-delivery-builder/go.mod
index 3d333a4d..cf46a190 100644
--- a/modules/mesh-delivery-builder/go.mod
+++ b/modules/mesh-delivery-builder/go.mod
@@ -13,6 +13,8 @@ require (
 	git.novox.be/novox/mesh-delivery/contracts/go/clients/meshdeliveryclient v0.0.0-00010101000000-000000000000
 	git.novox.be/novox/mesh-delivery/contracts/go/seats/git v0.0.0-00010101000000-000000000000
 	git.novox.be/novox/mesh-delivery/contracts/go/seats/meshbuilds v0.0.0-00010101000000-000000000000
+	git.novox.be/novox/mesh-delivery/contracts/go/seats/nodebuildgo v0.0.0-00010101000000-000000000000
+	git.novox.be/novox/mesh-delivery/contracts/go/seats/nodebuildnode v0.0.0-00010101000000-000000000000
 	git.novox.be/novox/mesh-delivery/contracts/go/seats/containerimageregistry v0.0.0-00010101000000-000000000000
 	git.novox.be/novox/mesh-delivery/contracts/go/seats/gopackageregistry v0.0.0-00010101000000-000000000000
 	git.novox.be/novox/mesh-delivery/contracts/go/seats/meshcatalog v0.0.0-00010101000000-000000000000
diff --git a/modules/mesh-delivery-builder/internal/build/fakes_test.go b/modules/mesh-delivery-builder/internal/build/fakes_test.go
index bd18bba5..fb490343 100644
--- a/modules/mesh-delivery-builder/internal/build/fakes_test.go
+++ b/modules/mesh-delivery-builder/internal/build/fakes_test.go
@@ -75,14 +75,9 @@ func presenceValue(t *testing.T, online bool) []byte {
 	return b
 }
 
-// tcValue is a toolchains value, as the build module's writer encodes it (mesh-sdk go/delivery EncodeToolchain).
-func tcValue(t *testing.T, language, version string) []byte {
-	t.Helper()
-	b, err := buildstep.EncodeToolchain(buildstep.Toolchain{Language: language, Version: version, Recipe: "1", At: time.Now().UTC()})
-	if err != nil {
-		t.Fatal(err)
-	}
-	return b
+// tcOf is a node's toolchain of a language, as the builder keeps what it heard.
+func tcOf(language, version string) buildstep.Toolchain {
+	return buildstep.Toolchain{Language: language, Version: version, Recipe: "1", At: time.Now().UTC()}
 }
 
 // tcs are the toolchain entries of a language on nodes, as the toolchains set gives them.
diff --git a/modules/mesh-delivery-builder/internal/build/run_test.go b/modules/mesh-delivery-builder/internal/build/run_test.go
index 4d28e0a9..1c471d37 100644
--- a/modules/mesh-delivery-builder/internal/build/run_test.go
+++ b/modules/mesh-delivery-builder/internal/build/run_test.go
@@ -180,8 +180,8 @@ func newRig(t *testing.T, artifacts ...catalogue.Artifact) *rig {
 	t.Helper()
 	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.tools.Set(n, tcOf("go", "go1.27.1"))
+		r.tools.Set(n, tcOf("typescript", "tsc5"))
 	}
 	r.asks = &buildrun.FakeAsks{Answer: r.answer}
 	r.b = &Builder{
@@ -235,8 +235,8 @@ func TestABundleAndAnArchiveAreBuiltOnOneNodeAndDone(t *testing.T) { // 1607/AC7
 	t.Run("ADR 0624: a done key keeps each form a counted node reads", aDoneKeyKeepsEachFormACountedNodeReads)
 	r := newRig(t, goBundle, archiveA, tsBundle)
 	// ADR 0584: a third node agrees with novox and ace's typescript is the odd one; the build is done and its step says ace sits out.
-	r.tools.Put(buildrun.NodeBuildModule, "g14.typescript", tcValue(t, "typescript", "tsc5"), false)
-	r.tools.Put(buildrun.NodeBuildModule, "ace.typescript", tcValue(t, "typescript", "tsc4"), false)
+	r.tools.Set("g14", tcOf("typescript", "tsc5"))
+	r.tools.Set("ace", tcOf("typescript", "tsc4"))
 	defer func() {
 		if st := r.st.vals[r.key]; !strings.Contains(string(st), "ace sits out: typescript tsc4, agreed tsc5") {
 			t.Errorf("the key does not say ace sits out: %s", st)
@@ -717,8 +717,8 @@ func TestAKeyIsBuiltOnlyWithTheToolchainItsFingerprintNamesAndNothingIsWrittenOt
 		t.Errorf("keys %v and %d calls for a recipe that differs or a value that names no toolchain", r.st.vals, len(r.bm.calls))
 	}
 	// The toolchain moves under a key that is not built yet: the old fingerprint stays unbuilt, the new one builds.
-	r.tools.Put(buildrun.GoBuildModule, "ace.go", tcValue(t, "go", "go1.27.2"), false)
-	r.tools.Put(buildrun.GoBuildModule, "novox.go", tcValue(t, "go", "go1.27.2"), false)
+	r.tools.Set("ace", tcOf("go", "go1.27.2"))
+	r.tools.Set("novox", tcOf("go", "go1.27.2"))
 	r.b.Reconsider(context.Background())
 	r.b.Wait()
 	if len(r.st.vals) != 0 {
@@ -740,11 +740,7 @@ func aRecipeThatMovesBuildsTheModuleAgainUnderItsNewFingerprint(t *testing.T) {
 	calls := len(r.bm.calls)
 	fp2 := "src2:" + hex64('2')
 	for _, n := range []string{"ace", "novox"} {
-		b, err := buildstep.EncodeToolchain(buildstep.Toolchain{Language: "go", Version: "go1.27.1", Recipe: "2", At: time.Now().UTC()})
-		if err != nil {
-			t.Fatal(err)
-		}
-		r.tools.Put(buildrun.GoBuildModule, n+".go", b, false)
+		r.tools.Set(n, buildstep.Toolchain{Language: "go", Version: "go1.27.1", Recipe: "2", At: time.Now().UTC()})
 	}
 	r.b.Reconsider(context.Background())
 	r.b.Wait()
@@ -772,7 +768,7 @@ func aRecipeThatMovesBuildsTheModuleAgainUnderItsNewFingerprint(t *testing.T) {
 
 func TestNodesTheyDisagreeOnLeaveTheKeyUnwritten(t *testing.T) { // 1615/AC4
 	r := newRig(t, goBundle)
-	r.tools.Put(buildrun.GoBuildModule, "ace.go", tcValue(t, "go", "go1.26.0"), false)
+	r.tools.Set("ace", tcOf("go", "go1.26.0"))
 	r.b.Module(context.Background(), "m", moduleValue(t, "modules/m"))
 	r.b.Wait()
 	if len(r.st.vals) != 0 || len(r.bm.calls) != 0 {
diff --git a/modules/mesh-delivery-builder/manifest_test.go b/modules/mesh-delivery-builder/manifest_test.go
index 5c6c1068..0b5e7521 100644
--- a/modules/mesh-delivery-builder/manifest_test.go
+++ b/modules/mesh-delivery-builder/manifest_test.go
@@ -102,13 +102,13 @@ func TestManifestDeclarations(t *testing.T) { // 1607/AC1
 	if m.Module != "mesh-delivery-builder" {
 		t.Errorf("module = %q", m.Module)
 	}
-	if want := []state{{Name: "builds", History: 5}, {Name: "engine-reads", History: 1}, {Name: "findings", History: 5}, {Name: "floor-waits", History: 1}, {Name: "hearing", History: 1}, {Name: "instances", History: 1}, {Name: "old-form", History: 1}, {Name: "bounds", History: 1, KeyTTL: true}, {Name: "queues", History: 1}, {Name: "reserved", History: 1}, {Name: "reasks", History: 1}, {Name: "versions", History: 1}, {Name: "first-views", History: 1}}; !reflect.DeepEqual(m.State, want) { // builds.BuilderBuildsHistory
+	if want := []state{{Name: "builds", History: 5}, {Name: "engine-reads", History: 1}, {Name: "findings", History: 5}, {Name: "floor-waits", History: 1}, {Name: "hearing", History: 1}, {Name: "instances", History: 1}, {Name: "old-form", History: 1}, {Name: "bounds", History: 1, KeyTTL: true}, {Name: "queues", History: 1}, {Name: "toolchains-heard", History: 1}, {Name: "reserved", History: 1}, {Name: "reasks", History: 1}, {Name: "versions", History: 1}, {Name: "first-views", History: 1}}; !reflect.DeepEqual(m.State, want) { // builds.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). Whether a
 	// node's machine is heard it asks the watchdogs seat's presence (issue 1966, ADR 0596 §2, ADR 0668 §3).
-	if want := []string{"mesh-build-go.steps", "mesh-build-go.toolchains", "mesh-build-image.steps", "mesh-build-node.steps", "mesh-build-node.toolchains",
+	if want := []string{"mesh-build-go.steps", "mesh-build-image.steps", "mesh-build-node.steps",
 		"mesh-delivery-assigner.assignments", "mesh-delivery-gate.source"}; !reflect.DeepEqual(sorted(m.Reads), want) {
 		t.Errorf("reads = %v, want %v", m.Reads, want)
 	}
@@ -137,18 +137,18 @@ func TestManifestDeclarations(t *testing.T) { // 1607/AC1
 		"seat:npm-package-registry.versions", "seat:oci-artifact-registry.remove", "seat:oci-artifact-registry.versions"}; !reflect.DeepEqual(sorted(m.Invokes), want) || len(m.Config) != 0 {
 		t.Errorf("invokes = %v, config = %v, want %v and no config", m.Invokes, m.Config, want)
 	}
-	// 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; and by the seat mesh-artifact-sweep's artifacts-gone, a blob the sweep found gone (1937/AC4, 1955/L7), the
+	// The builder hears the build seats' toolchain-reported and the node-engine seat's running (design 47 G §492, §546) and reads no
+	// build module's toolchains; and by the seat mesh-artifact-sweep's artifacts-gone, a blob the sweep found gone (1937/AC4, 1955/L7), the
 	// controller's no longer (1126/B9, ADR 0590).
 	// Design 51 *The floor*: the indexer's manifest-accepted and the condition keeper's condition-cleared wake a silent floor.
 	// DLV-B4: the four registry seats' outcomes, each a seat event `<seat>.<event>` on the shared events stream.
 	// DLV-M1: the indexer's and the assigner's views families of the states it follows.
 	if want := []string{"container-image-registry.kept", "container-image-registry.published", "container-image-registry.refused", "container-image-registry.removed",
 		"go-package-registry.kept", "go-package-registry.published", "go-package-registry.refused", "go-package-registry.removed",
-		"mesh-artifact-sweep.artifacts-gone", "mesh-build-go.toolchain.reported", "mesh-build-node.toolchain.reported", "mesh-catalog.manifest-accepted", "mesh-catalog.version-released", "mesh-catalog.versions-filled",
+		"mesh-artifact-sweep.artifacts-gone", "mesh-catalog.manifest-accepted", "mesh-catalog.version-released", "mesh-catalog.versions-filled",
 		"mesh-conditions.condition-cleared", "mesh-delivery-assigner.views.assignments", "mesh-delivery-forge-bridge.forge.**",
 		"mesh-delivery-indexer.views.candidates", "mesh-delivery-indexer.views.manifests", "mesh-delivery-indexer.views.modules",
-		"mesh-delivery-indexer.views.packages", "node-engine.manifest-reads-changed",
+		"mesh-delivery-indexer.views.packages", "node-build-go.toolchain-reported", "node-build-node.toolchain-reported", "node-engine.manifest-reads-changed", "node-engine.running",
 		"npm-package-registry.kept", "npm-package-registry.published", "npm-package-registry.refused", "npm-package-registry.removed",
 		"oci-artifact-registry.kept", "oci-artifact-registry.published", "oci-artifact-registry.refused", "oci-artifact-registry.removed"}; !reflect.DeepEqual(sorted(m.Consumes), want) {
 		t.Errorf("consumes = %v, want %v", m.Consumes, want)
@@ -161,7 +161,7 @@ func TestManifestDeclarations(t *testing.T) { // 1607/AC1
 	}
 	// 1945: the builder's tools (builder_seat_queue: note 62), served by its tools bundle, and the event it says when it asks an ask again.
 	if want := []string{"builder_announce_again", "builder_ask_again", "builder_bounds", "builder_build_again", "builder_builds_since", "builder_engine_reads", "builder_first_view_again", "builder_first_views",
-		"builder_floor_again", "builder_floor_waits", "builder_old_form", "builder_publish_again", "builder_reserved", "builder_reserved_drop", "builder_seat_queue", "builder_stuck", "builder_versions", "reserved"}; !reflect.DeepEqual(sorted(m.Tools), want) {
+		"builder_floor_again", "builder_floor_waits", "builder_old_form", "builder_publish_again", "builder_reserved", "builder_reserved_drop", "builder_seat_queue", "builder_stuck", "builder_toolchains", "builder_toolchains_drop", "builder_versions", "reserved"}; !reflect.DeepEqual(sorted(m.Tools), want) {
 		t.Errorf("tools = %v, want %v", m.Tools, want)
 	}
 	// Design 47 G §349: version.numbered is no longer said; old-form-closed on the family version, apart from the builds' ends.
diff --git a/modules/mesh-delivery-builder/module.json b/modules/mesh-delivery-builder/module.json
index f3d82244..3581b792 100644
--- a/modules/mesh-delivery-builder/module.json
+++ b/modules/mesh-delivery-builder/module.json
@@ -26,6 +26,8 @@
     "builder_reserved_drop",
     "builder_seat_queue",
     "builder_stuck",
+    "builder_toolchains",
+    "builder_toolchains_drop",
     "builder_versions",
     "reserved",
     "builder_first_views",
@@ -45,14 +47,15 @@
     "go-package-registry.refused",
     "go-package-registry.removed",
     "mesh-artifact-sweep.artifacts-gone",
-    "mesh-build-go.toolchain.reported",
-    "mesh-build-node.toolchain.reported",
     "mesh-catalog.manifest-accepted",
     "mesh-catalog.version-released",
     "mesh-catalog.versions-filled",
     "mesh-conditions.condition-cleared",
     "mesh-delivery-forge-bridge.forge.**",
+    "node-build-go.toolchain-reported",
+    "node-build-node.toolchain-reported",
     "node-engine.manifest-reads-changed",
+    "node-engine.running",
     "npm-package-registry.kept",
     "npm-package-registry.published",
     "npm-package-registry.refused",
@@ -103,6 +106,7 @@
     { "name": "old-form", "history": 1 },
     { "name": "bounds", "history": 1, "key-ttl": true },
     { "name": "queues", "history": 1 },
+    { "name": "toolchains-heard", "history": 1 },
     { "name": "reserved", "history": 1 },
     { "name": "reasks", "history": 1 },
     { "name": "versions", "history": 1 },
@@ -113,10 +117,8 @@
   ],
   "reads": [
     "mesh-build-go.steps",
-    "mesh-build-go.toolchains",
     "mesh-build-image.steps",
     "mesh-build-node.steps",
-    "mesh-build-node.toolchains",
     "mesh-delivery-assigner.assignments",
     "mesh-delivery-gate.source"
   ],