diff --git a/merge-check.sh b/merge-check.sh
new file mode 100644
index 0000000..37449c2
--- /dev/null
+++ b/merge-check.sh
@@ -0,0 +1,39 @@
+#!/bin/sh
+# mesh-check-toolchain: go
+#
+# The tool runtime's own check (novox/hq ADR 0237 as amended): the second layer of a pull request's merge
+# check, `mesh/repo-check`, run by the build seat in the mesh's Go toolchain — and by hand.
+#
+# The gate — every machine of the facts snapshot composed with this change — is the build seat's first
+# layer (`mesh/merge-gate`), run because the mesh's module graph builds node-tools and mesh-tools from
+# here. This is the code's own: node-tools (Go) formatted, vetted and its suite, every test on a bus of its
+# own at the release the mesh runs (internal/meshtest), packages in parallel, under the race detector when
+# the toolchain has a C compiler.
+#
+# **Said, never passed silently**: the runtime's and the console's tests launch TypeScript and Python
+# bundles that import the mesh's own package (@novox/mesh-sdk), which comes from the package registry — and
+# a check of code nobody has approved is given no credential for it. Where node and that package are not
+# present those two packages are not tested here, and the TypeScript in node-tools/src neither.
+set -eu
+cd node-tools
+
+unformatted=$(gofmt -l cmd internal)
+if [ -n "$unformatted" ]; then
+	echo "not gofmt'd:"
+	echo "$unformatted"
+	exit 1
+fi
+CGO_ENABLED=0 go vet ./...
+
+packages=$(go list ./...)
+if ! command -v node >/dev/null 2>&1 || [ ! -d node_modules/@novox/mesh-sdk ]; then
+	echo "NOT TESTED HERE: internal/runtime and internal/console launch bundles that need node and @novox/mesh-sdk"
+	packages=$(printf '%s\n' "$packages" | grep -v -e '/internal/runtime$' -e '/internal/console$')
+fi
+if command -v gcc >/dev/null 2>&1; then
+	CGO_ENABLED=1 go test -race -count=1 $packages
+else
+	echo "NOT RACE-CHECKED: the toolchain holds no C compiler; the suite runs without the race detector"
+	CGO_ENABLED=0 go test -count=1 $packages
+fi
+echo "NOT TESTED HERE: node-tools/src (TypeScript) needs @novox/mesh-sdk from the package registry"
diff --git a/node-tools/go.mod b/node-tools/go.mod
index 06b9b50..4395904 100644
--- a/node-tools/go.mod
+++ b/node-tools/go.mod
@@ -8,8 +8,15 @@ require (
 )
 
 require (
+	github.com/antithesishq/antithesis-sdk-go v0.7.0-default-no-op // indirect
+	github.com/google/go-tpm v0.9.8 // indirect
 	github.com/klauspost/compress v1.20.0 // indirect
+	github.com/minio/highwayhash v1.0.4 // indirect
+	github.com/nats-io/jwt/v2 v2.8.1 // indirect
+	github.com/nats-io/nats-server/v2 v2.11.17 // indirect
 	github.com/nats-io/nkeys v0.4.16 // indirect
 	github.com/nats-io/nuid v1.0.1 // indirect
+	go.uber.org/automaxprocs v1.6.0 // indirect
 	golang.org/x/crypto v0.57.0 // indirect
+	golang.org/x/time v0.15.0 // indirect
 )
diff --git a/node-tools/go.sum b/node-tools/go.sum
index 65100b8..2274dd5 100644
--- a/node-tools/go.sum
+++ b/node-tools/go.sum
@@ -1,12 +1,27 @@
+github.com/antithesishq/antithesis-sdk-go v0.7.0-default-no-op h1:Z/MZK75wC/NSrkgqeNIa7jexam9uWzhLmFTSCPI/kn0=
+github.com/antithesishq/antithesis-sdk-go v0.7.0-default-no-op/go.mod h1:FQyySiasQQM8735Ddel3MRojmy4dA1IqCeyJ5jmPMbI=
+github.com/google/go-tpm v0.9.8 h1:slArAR9Ft+1ybZu0lBwpSmpwhRXaa85hWtMinMyRAWo=
+github.com/google/go-tpm v0.9.8/go.mod h1:h9jEsEECg7gtLis0upRBQU+GhYVH6jMjrFxI8u6bVUY=
 github.com/klauspost/compress v1.20.0 h1:a3C1ke2ohxFymNlb2HWAHjDeKCI90scRskErZkR0ezA=
 github.com/klauspost/compress v1.20.0/go.mod h1:LUdAzn7YLVvxLpc7y3V1m40wESHTgc1422pwwBSKYuI=
+github.com/minio/highwayhash v1.0.4 h1:asJizugGgchQod2ja9NJlGOWq4s7KsAWr5XUc9Clgl4=
+github.com/minio/highwayhash v1.0.4/go.mod h1:GGYsuwP/fPD6Y9hMiXuapVvlIUEhFhMTh0rxU3ik1LQ=
+github.com/nats-io/jwt/v2 v2.8.1 h1:V0xpGuD/N8Mi+fQNDynXohVvp7ZztevW5io8CUWlPmU=
+github.com/nats-io/jwt/v2 v2.8.1/go.mod h1:nWnOEEiVMiKHQpnAy4eXlizVEtSfzacZ1Q43LIRavZg=
+github.com/nats-io/nats-server/v2 v2.11.17 h1:GKEghcFK6A+aFx11Yf1LjgLC3txAwvyhnYzhBIQZA8I=
+github.com/nats-io/nats-server/v2 v2.11.17/go.mod h1:B1sFVz4StNosQ903ak4N1G01Fl/9f8e06mXpFIE2K24=
 github.com/nats-io/nats.go v1.54.0 h1:vsXoOxjHp/GmPUN+EcI7uOf/uB+iAP+kEsAFNQN0yzA=
 github.com/nats-io/nats.go v1.54.0/go.mod h1:y+DZoD1oBOYfZTU681eTUiUjI0vbqYGixNVFHcjHJ0k=
 github.com/nats-io/nkeys v0.4.16 h1:rd5oAuLOb8mnAycB0xleuEBNS1pVVnN0fv/FF34Eypg=
 github.com/nats-io/nkeys v0.4.16/go.mod h1:llLgWoI0o4z/Q57q2R1kHfmocyhGV6VG/U18Glg1Afs=
 github.com/nats-io/nuid v1.0.1 h1:5iA8DT8V7q8WK2EScv2padNa/rTESc1KdnPw4TC2paw=
 github.com/nats-io/nuid v1.0.1/go.mod h1:19wcPz3Ph3q0Jbyiqsd0kePYG7A95tJPxeL+1OSON2c=
+go.uber.org/automaxprocs v1.6.0 h1:O3y2/QNTOdbF+e/dpXNNW7Rx2hZ4sTIPyybbxyNqTUs=
+go.uber.org/automaxprocs v1.6.0/go.mod h1:ifeIMSnPZuznNm6jmdzmU3/bfk01Fe2fotchwEFJ8r8=
 golang.org/x/crypto v0.57.0 h1:3ZVCjf8Ggz7zneR/EHRVx68Ctf+2pmIMP2UFhh9cC6M=
 golang.org/x/crypto v0.57.0/go.mod h1:Fdz0i5U6CoizGwLda9DttjSk6qlZo25zYNtR+ycvuZA=
+golang.org/x/sys v0.21.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
 golang.org/x/sys v0.48.0 h1:bbX/i/6MgT9BVLM9RT1thmxL04yeTAhbEz4SyadbXoo=
 golang.org/x/sys v0.48.0/go.mod h1:hNLxWAXmnKAxqDtdwIYC4bM9oQPEecfsnNMuSxOs3og=
+golang.org/x/time v0.15.0 h1:bbrp8t3bGUeFOx08pvsMYRTCVSMk89u4tKbNOZbp88U=
+golang.org/x/time v0.15.0/go.mod h1:Y4YMaQmXwGQZoFaVFk4YpCt4FLQMYKZe9oeV/f4MSno=
diff --git a/node-tools/internal/meshtest/meshtest.go b/node-tools/internal/meshtest/meshtest.go
index f5bc1bf..67b1bc9 100644
--- a/node-tools/internal/meshtest/meshtest.go
+++ b/node-tools/internal/meshtest/meshtest.go
@@ -1,9 +1,13 @@
 // Package meshtest raises what the controller would, for tests against a real bus: the ASSIGNMENTS
 // and EVENTS streams, memberships issued by hand, and a fixture's path.
 //
-// **The packages share one bus, so run them one at a time: `go test -p 1 ./...`.** Each test raises
-// the streams afresh, and the console discovers every runtime that announces itself on the bus
-// (novox/hq ADR 0197) — a runtime from another package's test is, correctly, found.
+// **Every test has a bus of its own** (novox/hq ADR 0237, the controller's internal/testbus): a server
+// linked in at the release go.mod pins — the release the mesh runs, held so by a test beside this one —
+// started for the one test and gone after it. The packages shared one bus and had to run one at a time:
+// each test raised the streams afresh, and the console discovers every runtime that announces itself on
+// the bus (ADR 0197), so a runtime from another package's test was, correctly, found. Now the suite runs
+// as Go runs it, in parallel and under the race detector. A person may still point a run at a bus of
+// their own with MESH_TEST_NATS_EXTERNAL=1 and MESH_TEST_NATS; then the run is theirs to serialise.
 package meshtest
 
 import (
@@ -12,24 +16,57 @@ import (
 	"path/filepath"
 	"runtime"
 	"strings"
+	"sync"
 	"testing"
 	"time"
 
+	"github.com/nats-io/nats-server/v2/server"
 	"github.com/nats-io/nats.go"
 
 	"github.com/novox/mesh-tools/node-tools/internal/bus"
 )
 
-// URL is the test bus, or the test is skipped.
+// Version is the release of the server the tests run.
+const Version = server.VERSION
+
+// URL is the bus of this test alone: started at its first ask, the same one at every ask after — a test
+// that dials twice, or hands the address to the code it tests, reaches one bus — and shut down when the
+// test ends.
 func URL(t *testing.T) string {
 	t.Helper()
-	url := os.Getenv("MESH_TEST_NATS")
-	if url == "" {
-		t.Skip("MESH_TEST_NATS unset")
+	if os.Getenv("MESH_TEST_NATS_EXTERNAL") == "1" {
+		if url := os.Getenv("MESH_TEST_NATS"); url != "" {
+			return url
+		}
+		t.Fatal("MESH_TEST_NATS_EXTERNAL=1 and MESH_TEST_NATS names no bus")
 	}
+	if url, ok := buses.Load(t); ok {
+		return url.(string)
+	}
+	opts := &server.Options{Host: "127.0.0.1", Port: server.RANDOM_PORT, JetStream: true, StoreDir: t.TempDir(),
+		NoLog: true, NoSigs: true}
+	s, err := server.NewServer(opts)
+	if err != nil {
+		t.Fatalf("a bus for this test could not be made: %v", err)
+	}
+	go s.Start()
+	if !s.ReadyForConnections(30 * time.Second) {
+		s.Shutdown()
+		t.Fatal("a bus for this test did not come up within 30s")
+	}
+	url := s.ClientURL()
+	buses.Store(t, url)
+	t.Cleanup(func() {
+		buses.Delete(t)
+		s.Shutdown()
+		s.WaitForShutdown()
+	})
 	return url
 }
 
+// buses are the running tests' buses, by test.
+var buses sync.Map
+
 // Mesh is the controller's job, done by hand.
 type Mesh struct {
 	nc *nats.Conn
diff --git a/node-tools/internal/meshtest/meshtest_test.go b/node-tools/internal/meshtest/meshtest_test.go
new file mode 100644
index 0000000..220557e
--- /dev/null
+++ b/node-tools/internal/meshtest/meshtest_test.go
@@ -0,0 +1,75 @@
+package meshtest
+
+import (
+	"encoding/json"
+	"os"
+	"path/filepath"
+	"regexp"
+	"strings"
+	"testing"
+)
+
+// **The bus the tests run is the bus the mesh runs** (novox/hq ADR 0227 rule 9, ADR 0237): the server linked
+// into the tests is held to the release the catalogue's bus image is — read from beside this checkout, as
+// the build seat clones it for a merge check — and, given the facts snapshot, to the release the mesh's bus
+// server says it runs. A bus upgrade moves the catalogue's pin; this then fails until go.mod's moves with it.
+func TestTheBusTheTestsRunIsTheBusTheMeshRuns(t *testing.T) {
+	beside := os.Getenv("MESH_CHECK_BESIDE")
+	if beside == "" {
+		beside = filepath.Join("..", "..", "..", "..")
+	}
+	dockerfile := filepath.Join(beside, "mesh-catalog", "modules", "nats", "Dockerfile")
+	raw, err := os.ReadFile(dockerfile)
+	switch {
+	case err == nil:
+		pinned := regexp.MustCompile(`upstream: nats ([0-9.]+)-alpine`).FindSubmatch(raw)
+		if pinned == nil {
+			t.Fatalf("%s says no release its digest is", dockerfile)
+		}
+		if string(pinned[1]) != Version {
+			t.Errorf("the tests run bus %s and the catalogue's bus image is %s: move go.mod's nats-server pin with the image",
+				Version, pinned[1])
+		}
+	case os.IsNotExist(err):
+		t.Logf("the catalogue is not beside this checkout, so its bus image is not compared")
+	default:
+		t.Fatal(err)
+	}
+	path := os.Getenv("MESH_FACTS")
+	if path == "" {
+		t.Logf("no MESH_FACTS: the bus the mesh runs is compared in a merge check, which has it")
+		return
+	}
+	body, err := os.ReadFile(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	var f struct {
+		Taken    string `json:"taken"`
+		Versions struct {
+			Bus string `json:"bus"`
+		} `json:"versions"`
+	}
+	if err := json.Unmarshal(body, &f); err != nil {
+		t.Fatal(err)
+	}
+	if f.Versions.Bus != "" && strings.TrimPrefix(f.Versions.Bus, "v") != Version {
+		t.Errorf("the tests run bus %s and the mesh's bus runs %s (facts of %s)", Version, f.Versions.Bus, f.Taken)
+	}
+}
+
+// Each test is given a bus of its own, and the same one at every ask.
+func TestEachTestHasABusOfItsOwn(t *testing.T) {
+	var first string
+	t.Run("one", func(t *testing.T) {
+		first = URL(t)
+		if URL(t) != first {
+			t.Fatal("two buses for one test")
+		}
+	})
+	t.Run("two", func(t *testing.T) {
+		if URL(t) == first {
+			t.Fatal("two tests were given one bus")
+		}
+	})
+}