node-tools in Go: the node's runtime, launch-only, wire-compatible with the TypeScript (hq ADR 0193)

The runtime knows no language, so nothing ties it to Node.js. This ports its serve mode — the
pinned bus connection and patient connect, following memberships, launching every served bundle
over MCP on stdio with its own environment, a child's emit published as its module, each tool,
the tools verb and seat verbs served where the mesh issued them, and the console on loopback —
to one static binary. Same subjects, request and reply bodies, event headers and MCP answers.
The TypeScript stays: it is still the runtime inside the per-module containers until WP4c.
Tests run against a real bus and share the TypeScript fixtures.

node-tools/internal/meshtest/meshtest.go

@@ -0,0 +1,143 @@
+// 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.
+package meshtest
+
+import (
+	"encoding/json"
+	"os"
+	"path/filepath"
+	"runtime"
+	"strings"
+	"testing"
+	"time"
+
+	"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.
+func URL(t *testing.T) string {
+	t.Helper()
+	url := os.Getenv("MESH_TEST_NATS")
+	if url == "" {
+		t.Skip("MESH_TEST_NATS unset")
+	}
+	return url
+}
+
+// Mesh is the controller's job, done by hand.
+type Mesh struct {
+	nc *nats.Conn
+	js nats.JetStreamContext
+}
+
+// New raises the streams afresh.
+func New(t *testing.T) *Mesh {
+	t.Helper()
+	nc, err := nats.Connect(URL(t))
+	if err != nil {
+		t.Fatal(err)
+	}
+	js, _ := nc.JetStream()
+	for _, s := range []string{"ASSIGNMENTS", "EVENTS"} {
+		_ = js.DeleteStream(s)
+	}
+	if _, err := js.AddStream(&nats.StreamConfig{Name: "ASSIGNMENTS", Subjects: []string{"mesh.assignment.>"},
+		MaxMsgsPerSubject: 1, AllowDirect: true}); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := js.AddStream(&nats.StreamConfig{Name: "EVENTS", Subjects: []string{"mesh.mod.*.event.>"}}); err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(nc.Close)
+	return &Mesh{nc: nc, js: js}
+}
+
+// Issue publishes a membership.
+func (m *Mesh) Issue(t *testing.T, mem bus.Membership) {
+	t.Helper()
+	body, _ := json.Marshal(mem)
+	if _, err := m.js.Publish(bus.MembershipSubject(mem.Node, mem.Module), body); err != nil {
+		t.Fatal(err)
+	}
+}
+
+// NextEvent is the subject the next event under a pattern lands on.
+func (m *Mesh) NextEvent(t *testing.T, pattern string) <-chan string {
+	t.Helper()
+	ch := make(chan string, 1)
+	sub, err := m.nc.Subscribe(pattern, func(msg *nats.Msg) {
+		select {
+		case ch <- msg.Subject:
+		default:
+		}
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(func() { _ = sub.Unsubscribe() })
+	_ = m.nc.Flush()
+	return ch
+}
+
+// MembershipOf is a membership as the controller issues one on a machine.
+func MembershipOf(module, node string, plain bool, seats map[string][]string) bus.Membership {
+	own := "mesh.mod." + module
+	serves := []bus.Served{{Subject: own + ".tool.{tool}." + node}}
+	if plain {
+		serves = append(serves, bus.Served{Subject: own + ".tool.{tool}", Queue: "serve." + module})
+	}
+	var verbs []bus.SeatVerb
+	for seat, vs := range seats {
+		for _, v := range vs {
+			verbs = append(verbs, bus.SeatVerb{Seat: seat, Verb: v, Subject: "mesh.seat." + seat + ".tool." + v + "." + node})
+		}
+	}
+	return bus.Membership{Node: node, Module: module, Serves: serves, Seats: verbs,
+		Emits: own + ".event.{event}", Tools: own + ".tool.tools"}
+}
+
+// Fixture is a path in node-tools/test/fixtures, which these tests share with the TypeScript ones.
+func Fixture(name string) string {
+	_, here, _, _ := runtime.Caller(0)
+	return filepath.Join(filepath.Dir(here), "..", "..", "test", "fixtures", name)
+}
+
+// Until retries while the bus answers "no responders" — something not yet served.
+func Until(t *testing.T, try func() error) {
+	t.Helper()
+	var err error
+	for i := 0; i < 50; i++ {
+		if err = try(); err == nil {
+			return
+		}
+		time.Sleep(100 * time.Millisecond)
+	}
+	t.Fatal(err)
+}
+
+// Logs collects what the runtime says.
+type Logs struct{ lines []string }
+
+// Logf is a logger that keeps the lines.
+func (l *Logs) Logf(format string, args ...any) {
+	l.lines = append(l.lines, sprintf(format, args...))
+}
+
+// Has says whether a line contains every fragment.
+func (l *Logs) Has(fragments ...string) bool {
+	for _, line := range l.lines {
+		all := true
+		for _, f := range fragments {
+			all = all && strings.Contains(line, f)
+		}
+		if all {
+			return true
+		}
+	}
+	return false
+}
+
+// All is every line.
+func (l *Logs) All() string { return strings.Join(l.lines, "\n") }