diff --git a/modules/mesh-delivery-builder/buildrun/names.go b/modules/mesh-delivery-builder/buildrun/names.go
index 770324f8..79def2fb 100644
--- a/modules/mesh-delivery-builder/buildrun/names.go
+++ b/modules/mesh-delivery-builder/buildrun/names.go
@@ -5,7 +5,8 @@ package buildrun
 // names a holder (novox/hq ADR 0625 §4, ADR 0634 §1).
 const (
 	// PlacementBucket is the assigner's state placement, which the toolchain gate reads for the placing of a build module.
-	PlacementBucket = "mesh-delivery-assigner_placement"
+	AssignerModule  = "mesh-delivery-assigner"
+	PlacementBucket = AssignerModule + "_placement"
 )
 
 // StepsBucket is the bucket of a build module's state steps.
diff --git a/modules/mesh-delivery-builder/buildrun/standing.go b/modules/mesh-delivery-builder/buildrun/standing.go
index 19913896..adc4adb0 100644
--- a/modules/mesh-delivery-builder/buildrun/standing.go
+++ b/modules/mesh-delivery-builder/buildrun/standing.go
@@ -13,7 +13,7 @@ import (
 	"github.com/nats-io/nats.go/jetstream"
 
 	"git.novox.be/novox/mesh-contracts/placement/go/clients/meshmoduleassignerclient"
-	"git.novox.be/novox/mesh-delivery/contracts/go/seats/nodebuildgo"
+	"git.novox.be/novox/mesh-delivery/sdk/buildstep"
 	"git.novox.be/novox/mesh-sdk/go/process"
 )
 
@@ -136,7 +136,7 @@ func (g *ToolchainGate) again(node string, modules []string) bool {
 			continue
 		}
 		for _, k := range slices.Sorted(maps.Keys(g.raw[module])) {
-			if n, _, ok := nodebuildgo.ParseToolchainsByNodeLanguageKey(k); ok && n == node {
+			if n, _, err := buildstep.ParseToolchainKey(k); err == nil && n == node {
 				changed = g.pass(module, k) || changed
 			}
 		}
@@ -151,9 +151,9 @@ func (g *ToolchainGate) pass(module, key string) bool {
 	if !held {
 		return g.forward(module, key, nil, true)
 	}
-	node, _, ok := nodebuildgo.ParseToolchainsByNodeLanguageKey(key)
+	node, _, err := buildstep.ParseToolchainKey(key)
 	why := ""
-	if ok && g.known && g.placed.Seeded() {
+	if err == nil && g.known && g.placed.Seeded() {
 		why = g.leftOut(module, node, value)
 	}
 	if why == "" {
@@ -175,8 +175,8 @@ func (g *ToolchainGate) leftOut(module, node string, value []byte) string {
 	if !placed {
 		return fmt.Sprintf("the catalogue does not place %s on %s, so it is no builder", module, node)
 	}
-	tc, err := nodebuildgo.DecodeToolchainsByNodeLanguageValue(value)
-	if err == nil && tc.At != nil && tc.At.Before(since) {
+	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)
 	}
diff --git a/modules/mesh-delivery-builder/buildrun/standing_test.go b/modules/mesh-delivery-builder/buildrun/standing_test.go
index 47093903..0ac7afeb 100644
--- a/modules/mesh-delivery-builder/buildrun/standing_test.go
+++ b/modules/mesh-delivery-builder/buildrun/standing_test.go
@@ -3,7 +3,6 @@ package buildrun
 import (
 	"bytes"
 	"context"
-	"encoding/json"
 	"errors"
 	"fmt"
 	"log"
@@ -15,14 +14,13 @@ import (
 
 	"git.novox.be/novox/mesh-contracts/placement/go/clients/meshmoduleassignerclient"
 	"git.novox.be/novox/mesh-contracts/placement/go/seats/meshmoduleassigner"
-	"git.novox.be/novox/mesh-delivery/contracts/go/seats/nodebuildgo"
 	"git.novox.be/novox/mesh-delivery/sdk/buildstep"
 )
 
 func gateReport(t *testing.T, node, version string, at time.Time) (string, []byte) {
 	t.Helper()
-	key := nodebuildgo.ToolchainsByNodeLanguageKey(node, "typescript")
-	value, err := json.Marshal(nodebuildgo.Toolchain{Language: "typescript", Version: version, Recipe: "f59571cf4be75adf", At: &at})
+	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)
 	}
diff --git a/modules/mesh-delivery-builder/buildrun/toolchains.go b/modules/mesh-delivery-builder/buildrun/toolchains.go
index acd8089b..a37200b9 100644
--- a/modules/mesh-delivery-builder/buildrun/toolchains.go
+++ b/modules/mesh-delivery-builder/buildrun/toolchains.go
@@ -3,7 +3,6 @@ package buildrun
 import (
 	"sync"
 
-	"git.novox.be/novox/mesh-delivery/contracts/go/seats/nodebuildgo"
 	"git.novox.be/novox/mesh-delivery/sdk/buildstep"
 )
 
@@ -14,7 +13,7 @@ var LanguageOf = map[string]string{GoBuildModule: "go", NodeBuildModule: "typesc
 // put them in. Safe for use from the watches and from a build at once.
 type ToolchainSet struct {
 	mu sync.Mutex
-	by map[string]map[string]nodebuildgo.ToolchainsByNodeLanguageValue // language -> node -> entry
+	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
@@ -25,8 +24,8 @@ func (s *ToolchainSet) Put(module, key string, value []byte, deleted bool) bool
 	if !ok {
 		return false
 	}
-	node, keyLanguage, ok := nodebuildgo.ParseToolchainsByNodeLanguageKey(key)
-	if !ok || keyLanguage != language {
+	node, keyLanguage, err := buildstep.ParseToolchainKey(key)
+	if err != nil || keyLanguage != language {
 		return false
 	}
 	s.mu.Lock()
@@ -38,15 +37,15 @@ func (s *ToolchainSet) Put(module, key string, value []byte, deleted bool) bool
 		delete(s.by[language], node)
 		return true
 	}
-	tc, err := nodebuildgo.DecodeToolchainsByNodeLanguageValue(value)
+	tc, err := buildstep.DecodeToolchain(value)
 	if err != nil || tc.Language != language {
 		return false
 	}
 	if s.by == nil {
-		s.by = map[string]map[string]nodebuildgo.ToolchainsByNodeLanguageValue{}
+		s.by = map[string]map[string]buildstep.Toolchain{}
 	}
 	if s.by[language] == nil {
-		s.by[language] = map[string]nodebuildgo.ToolchainsByNodeLanguageValue{}
+		s.by[language] = map[string]buildstep.Toolchain{}
 	}
 	cur, had := s.by[language][node]
 	s.by[language][node] = tc
@@ -59,7 +58,7 @@ func (s *ToolchainSet) Entries(language string) []buildstep.NodeToolchain {
 	defer s.mu.Unlock()
 	var out []buildstep.NodeToolchain
 	for node, tc := range s.by[language] {
-		out = append(out, buildstep.NodeToolchain{Node: node, Toolchain: buildstep.Toolchain{Language: tc.Language, Version: tc.Version, Recipe: tc.Recipe}})
+		out = append(out, buildstep.NodeToolchain{Node: node, Toolchain: tc})
 	}
 	return out
 }
diff --git a/modules/mesh-delivery-builder/buildrun/toolchains_test.go b/modules/mesh-delivery-builder/buildrun/toolchains_test.go
index ebf796ac..72aeab92 100644
--- a/modules/mesh-delivery-builder/buildrun/toolchains_test.go
+++ b/modules/mesh-delivery-builder/buildrun/toolchains_test.go
@@ -1,17 +1,16 @@
 package buildrun
 
 import (
-	"encoding/json"
 	"testing"
 	"time"
 
-	"git.novox.be/novox/mesh-delivery/contracts/go/seats/nodebuildgo"
+	"git.novox.be/novox/mesh-delivery/sdk/buildstep"
 )
 
 func tcValue(t *testing.T, language, version string) []byte {
 	t.Helper()
 	now := time.Now()
-	b, err := json.Marshal(nodebuildgo.Toolchain{Language: language, Version: version, Recipe: "1", At: &now})
+	b, err := buildstep.EncodeToolchain(buildstep.Toolchain{Language: language, Version: version, Recipe: "1", At: now})
 	if err != nil {
 		t.Fatal(err)
 	}
diff --git a/sdk/buildstep/toolchains.go b/sdk/buildstep/toolchains.go
index 00d49555..024bf935 100644
--- a/sdk/buildstep/toolchains.go
+++ b/sdk/buildstep/toolchains.go
@@ -77,3 +77,15 @@ func AgreedToolchain(entries []NodeToolchain) (tc Toolchain, none string) {
 	a := ToolchainAgreement(entries)
 	return a.Toolchain, a.Wait
 }
+
+// ParseToolchainKey is the inverse of ToolchainKey.
+func ParseToolchainKey(key string) (node, language string, err error) {
+	node, language, ok := strings.Cut(key, ".")
+	if !ok {
+		return "", "", fmt.Errorf("buildstep: %q is not a toolchain key, <node>.<language>", key)
+	}
+	if _, err := ToolchainKey(node, language); err != nil {
+		return "", "", fmt.Errorf("buildstep: %q is not a toolchain key: %w", key, err)
+	}
+	return node, language, nil
+}
diff --git a/sdk/buildstep/toolchains_test.go b/sdk/buildstep/toolchains_test.go
index a1f376ef..094c7903 100644
--- a/sdk/buildstep/toolchains_test.go
+++ b/sdk/buildstep/toolchains_test.go
@@ -56,3 +56,18 @@ func TestToolchainAgreement(t *testing.T) {
 		}
 	}
 }
+
+func TestToolchainKeyParsesBack(t *testing.T) {
+	key, err := ToolchainKey("ace", "go")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if node, lang, err := ParseToolchainKey(key); err != nil || node != "ace" || lang != "go" {
+		t.Errorf("%q parsed to %q %q %v", key, node, lang, err)
+	}
+	for _, bad := range []string{"ace", "ace.rust", ".go", "a.b.go"} {
+		if _, _, err := ParseToolchainKey(bad); err == nil {
+			t.Errorf("%q parsed", bad)
+		}
+	}
+}