diff --git a/internal/builder/builder.go b/internal/builder/builder.go
index 8658b65..fe6c754 100644
--- a/internal/builder/builder.go
+++ b/internal/builder/builder.go
@@ -129,7 +129,7 @@ func Build(ctx context.Context, run Runner, publish Publisher,
 		// logs can be compared.
 		sort.Slice(artifacts, func(i, j int) bool { return artifacts[i].Name < artifacts[j].Name })
 		for _, a := range artifacts {
-			made, err := one(ctx, run, publish, manifest.Module, within, commit, a, args)
+			made, err := one(ctx, run, publish, manifest.Module, within, commit, a, args, held)
 			if err != nil {
 				return Result{}, err
 			}
@@ -215,7 +215,8 @@ func against(within string, manifest catalogue.Manifest) []string {
 const ManifestName = "module.json"
 
 func one(ctx context.Context, run Runner, publish Publisher,
-	module, tree, commit string, a catalogue.Artifact, args []string) (catalogue.Built, error) {
+	module, tree, commit string, a catalogue.Artifact, args []string,
+	held map[string]string) (catalogue.Built, error) {
 
 	switch a.Kind {
 	case catalogue.ArtifactUpstream:
@@ -252,6 +253,46 @@ func one(ctx context.Context, run Runner, publish Publisher,
 		}
 		return catalogue.Built{Name: a.Name, Kind: a.Kind, Reference: reference}, nil
 
+	case catalogue.ArtifactBundle:
+		// **The one recipe that both builds and packs.** Everything else either produces an image
+		// or packs what is already there; this compiles the module's own code first, in a
+		// toolchain the mesh chose from what the module said it was written in, and packs the
+		// result.
+		//
+		// The compiler runs in a container rather than on the build machine, for the reason every
+		// other build does: what a build needs installed is the toolchain's business, and a build
+		// machine that accumulated one toolchain per language would be a machine nobody could
+		// reproduce.
+		chain, err := ToolchainFor(a.Language)
+		if err != nil {
+			return catalogue.Built{}, fmt.Errorf("%s: %s: %w", module, a.Name, err)
+		}
+		base, ok := held[chain.Base+"/"+chain.Artifact]
+		if !ok {
+			// Named, not pinned: the mesh answers with the copy it holds. Refused before anything
+			// is built, saying which module has to exist first, rather than failing inside a
+			// compile with a message about an image (novox/hq 04-ISSUES/044).
+			return catalogue.Built{}, fmt.Errorf(
+				"%s: %s is written in %s, which is compiled by %s's %q artifact, and this mesh "+
+					"holds no copy of it. Build %s first",
+				module, a.Name, chain.Language, chain.Base, chain.Artifact, chain.Base)
+		}
+		compiled, err := compile(ctx, run, tree, chain, base, a)
+		if err != nil {
+			return catalogue.Built{}, fmt.Errorf("%s: compiling %s failed: %w", module, a.Name, err)
+		}
+		body, err := pack(compiled)
+		if err != nil {
+			return catalogue.Built{}, fmt.Errorf("%s: packing %s failed: %w", module, a.Name, err)
+		}
+		sum := sha256.Sum256(body)
+		digest := "sha256:" + hex.EncodeToString(sum[:])
+		where, err := publish.PublishArchive(ctx, module+"/"+a.Name, body, digest)
+		if err != nil {
+			return catalogue.Built{}, err
+		}
+		return catalogue.Built{Name: a.Name, Kind: a.Kind, Reference: where, Digest: digest}, nil
+
 	case catalogue.ArtifactArchive:
 		body, err := pack(filepath.Join(tree, a.From))
 		if err != nil {
@@ -406,3 +447,47 @@ func standingOn(manifest catalogue.Manifest, held map[string]string) ([]string,
 	}
 	return args, nil
 }
+
+// compile runs a module's own code through its toolchain, and says where the result is.
+//
+// **In the module's own directory, under the path the toolchain expects.** A module is compiled
+// where its dependencies resolve upward into the base's own library directory, so what it is
+// compiled against is exactly what it will run against — the reason every hand-written Dockerfile
+// had to choose a working directory carefully, and the reason none of them has to now.
+func compile(ctx context.Context, run Runner, tree string, chain Toolchain,
+	base string, a catalogue.Artifact) (string, error) {
+
+	// Where inside the toolchain the module's source is mounted, and where its output lands. Fixed
+	// rather than configurable: a module that could move this would be describing its own build.
+	const within = "/app/modules/module"
+
+	invocation := []string{
+		"run", "--rm",
+		"--volume", tree + ":" + within,
+		"--workdir", within,
+		base,
+	}
+	invocation = append(invocation, chain.Compile...)
+	// What to compile. Named by the module rather than discovered, so adding a file does not
+	// silently change what a build produces.
+	if len(a.Entrypoints) > 0 {
+		invocation = append(invocation, sourcesFor(a.Entrypoints)...)
+	}
+	if _, err := run(ctx, tree, "docker", invocation...); err != nil {
+		return "", err
+	}
+	return filepath.Join(tree, chain.Output), nil
+}
+
+// sourcesFor turns compiled entrypoints back into what to compile.
+//
+// A module names what a tool host should LOAD — compiled paths under the bundle's root — because
+// that is the thing anything else needs to know. What to compile is the same list with the
+// language's own extension, which is the toolchain's business rather than the module's.
+func sourcesFor(entrypoints []string) []string {
+	out := make([]string, 0, len(entrypoints))
+	for _, e := range entrypoints {
+		out = append(out, strings.TrimSuffix(e, filepath.Ext(e))+".ts")
+	}
+	return out
+}
diff --git a/internal/builder/bundle_test.go b/internal/builder/bundle_test.go
new file mode 100644
index 0000000..2f40ba9
--- /dev/null
+++ b/internal/builder/bundle_test.go
@@ -0,0 +1,109 @@
+package builder
+
+import (
+	"context"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+const aBundle = `{"module":"greeter","version":"1",
+  "build":{"artifacts":[
+    {"name":"code","kind":"bundle","language":"typescript","entrypoints":["dist/index.js"]}]},
+  "resources":[
+    {"id":"files","type":"archive","path":"/opt/greeter","artifact":"code"}]}`
+
+// compiling is a runner that behaves like a toolchain: when asked to compile, it leaves output
+// where the toolchain says output lands. Without this the pack step has nothing to pack, and the
+// test would be asserting on a failure rather than on a build.
+type compiling struct{ *recorded }
+
+func (c compiling) run(ctx context.Context, dir, name string, args ...string) (string, error) {
+	out, err := c.recorded.run(ctx, dir, name, args...)
+	if name == "docker" && len(args) > 0 && args[0] == "run" {
+		made := filepath.Join(dir, "dist")
+		if err := os.MkdirAll(made, 0o755); err != nil {
+			return "", err
+		}
+		if err := os.WriteFile(filepath.Join(made, "index.js"), []byte("console.log(1)"), 0o644); err != nil {
+			return "", err
+		}
+	}
+	return out, err
+}
+
+// **A module says what it is written in, and needs no Dockerfile.** This is the whole point of the
+// bundle recipe: the same module previously needed a hand-written recipe repeating an incantation
+// that is easy to get wrong in ways that fail somewhere else.
+func TestABundleIsCompiledAndPackedWithNoDockerfile(t *testing.T) {
+	r, workspace := aRepository(t, aBundle, map[string]string{"index.ts": "console.log(1)"})
+	held := map[string]string{"mesh-tools/build": "registry.invalid/mesh-tools/build@sha256:" + strings.Repeat("b", 64)}
+
+	got, err := Build(context.Background(), compiling{r}.run, r,
+		"https://forge.invalid/greeter.git", "", "", workspace, held)
+	if err != nil {
+		t.Fatalf("a module with a language and no Dockerfile did not build: %v", err)
+	}
+
+	// Compiled in the toolchain the mesh chose, not in one the module named.
+	var compiled string
+	for _, line := range r.ran {
+		if strings.HasPrefix(line, "docker run") {
+			compiled = line
+		}
+	}
+	if compiled == "" {
+		t.Fatalf("nothing was compiled:\n%s", strings.Join(r.ran, "\n"))
+	}
+	if !strings.Contains(compiled, "mesh-tools/build@sha256:") {
+		t.Fatalf("the compile did not run in the mesh's own toolchain: %s", compiled)
+	}
+	if strings.Contains(strings.Join(r.ran, "\n"), "docker build") {
+		t.Fatalf("a bundle invoked a Dockerfile build, which is the thing it exists to avoid:\n%s",
+			strings.Join(r.ran, "\n"))
+	}
+
+	// And pinned by a digest of what came out, like any other artifact.
+	digest, _ := got.Manifest.Resources[0]["digest"].(string)
+	if !strings.HasPrefix(digest, "sha256:") {
+		t.Fatalf("the bundle was not pinned: %v", got.Manifest.Resources[0])
+	}
+}
+
+// **Refused before anything is built, naming what to build first.** A base the mesh has not built
+// is not a compile that fails on its first line — it is a question somebody can answer, and saying
+// it early is the difference between a fixable message and one about a missing image.
+func TestABundleWhoseToolchainIsNotHeldIsRefusedFirst(t *testing.T) {
+	r, workspace := aRepository(t, aBundle, map[string]string{"index.ts": "console.log(1)"})
+
+	_, err := Build(context.Background(), compiling{r}.run, r,
+		"https://forge.invalid/greeter.git", "", "", workspace, nil)
+	if err == nil {
+		t.Fatal("a bundle was built with no toolchain to compile it in")
+	}
+	if !strings.Contains(err.Error(), "mesh-tools") {
+		t.Fatalf("the refusal does not name what has to be built first: %v", err)
+	}
+	for _, line := range r.ran {
+		if strings.HasPrefix(line, "docker run") {
+			t.Fatalf("a compile was attempted before the refusal: %s", line)
+		}
+	}
+}
+
+// A language the mesh does not build is refused the same way, and names what it can build.
+func TestABundleInAnUnknownLanguageIsRefused(t *testing.T) {
+	manifest := strings.Replace(aBundle, `"language":"typescript"`, `"language":"cobol"`, 1)
+	r, workspace := aRepository(t, manifest, map[string]string{"index.ts": "x"})
+
+	_, err := Build(context.Background(), compiling{r}.run, r,
+		"https://forge.invalid/greeter.git", "", "", workspace,
+		map[string]string{"mesh-tools/build": "registry.invalid/x@sha256:" + strings.Repeat("c", 64)})
+	if err == nil {
+		t.Fatal("a language nothing can compile was accepted")
+	}
+	if !strings.Contains(err.Error(), "typescript") {
+		t.Fatalf("the refusal does not say what would have worked: %v", err)
+	}
+}
diff --git a/internal/builder/toolchain.go b/internal/builder/toolchain.go
new file mode 100644
index 0000000..2d23d19
--- /dev/null
+++ b/internal/builder/toolchain.go
@@ -0,0 +1,99 @@
+package builder
+
+import (
+	"fmt"
+	"sort"
+	"strings"
+)
+
+// What a language implies, so a module does not have to say it.
+//
+// **A module says what it is written in; this says what that means.** The alternative is what the
+// mesh had: every module carrying a Dockerfile that repeated the same incantation, and most of the
+// catalogue never converted because the incantation is easy to get wrong in ways that fail
+// somewhere else (novox/hq 03-DESIGN/01-to-be/18-building-a-module.md).
+//
+// A toolchain is deliberately not configurable by the module. Anything a module could override
+// here it would be writing a Dockerfile to override, and then this bought nothing.
+
+// Toolchain is how one language is compiled into a bundle.
+type Toolchain struct {
+	// Language is what a module declares to select this.
+	Language string
+	// Base is the module whose artifact provides the compiler, named rather than pinned: the mesh
+	// answers with the copy it holds, so a recipe never names one particular build of it
+	// (novox/hq 04-ISSUES/044).
+	Base string
+	// Artifact is which of that module's artifacts is the compiling one.
+	Artifact string
+	// Compile is what runs inside it, relative to the module's own directory. The output goes to
+	// Output, which is what gets packed.
+	Compile []string
+	// Output is the directory the compiled result lands in, relative to the module's directory.
+	Output string
+}
+
+// toolchains is every language the mesh can build.
+//
+// **A closed list, and adding to it is a decision rather than a configuration.** Every language is
+// permanent: it needs an SDK carrying the broker client, sealed-credential reading, the event
+// envelope and tool serving, and the contracts every module shares change rarely and cascade when
+// they do (novox/hq ADR 0039). A mesh whose languages disagree about the envelope fails by ignoring
+// messages rather than by failing to compile, so a new entry here is a commitment to keeping N
+// implementations of one contract in step.
+var toolchains = []Toolchain{
+	{
+		Language: "typescript",
+		Base:     "mesh-tools",
+		Artifact: "build",
+		// Invoked by its real path rather than through node_modules/.bin, whose entries are
+		// symlinks to a launcher that requires its library relatively — and the base image's own
+		// assembly resolves them away, leaving a launcher whose relative require points nowhere.
+		// Every module's hand-written Dockerfile had to know this. Now none of them does.
+		Compile: []string{
+			"node", "/app/node_modules/typescript/bin/tsc",
+			"--module", "NodeNext", "--moduleResolution", "NodeNext",
+			"--target", "ES2022", "--outDir", "dist",
+		},
+		Output: "dist",
+	},
+}
+
+// ToolchainFor is what builds this language, or says what it can build.
+func ToolchainFor(language string) (Toolchain, error) {
+	want := strings.ToLower(strings.TrimSpace(language))
+	if want == "" {
+		return Toolchain{}, fmt.Errorf(
+			"a bundle must say what language it is written in: the mesh chooses the compiler, and "+
+				"it cannot choose one for a module that has not said. It can build %s", spoken())
+	}
+	for _, t := range toolchains {
+		if t.Language == want {
+			return t, nil
+		}
+	}
+	return Toolchain{}, fmt.Errorf(
+		"%q is not a language this mesh builds. It can build %s — and adding one is a decision "+
+			"rather than a setting, because every language is another implementation of the "+
+			"contracts every module shares", language, spoken())
+}
+
+// spoken lists the languages, so a refusal says what would have worked.
+func spoken() string {
+	names := make([]string, 0, len(toolchains))
+	for _, t := range toolchains {
+		names = append(names, t.Language)
+	}
+	sort.Strings(names)
+	return strings.Join(names, ", ")
+}
+
+// Languages is every language the mesh can build, for anything that wants to say so.
+func Languages() []string {
+	names := make([]string, 0, len(toolchains))
+	for _, t := range toolchains {
+		names = append(names, t.Language)
+	}
+	sort.Strings(names)
+	return names
+}
diff --git a/internal/builder/toolchain_test.go b/internal/builder/toolchain_test.go
new file mode 100644
index 0000000..e387de3
--- /dev/null
+++ b/internal/builder/toolchain_test.go
@@ -0,0 +1,56 @@
+package builder
+
+import (
+	"strings"
+	"testing"
+)
+
+// A language the mesh builds resolves to the toolchain that builds it.
+func TestADeclaredLanguageSelectsItsToolchain(t *testing.T) {
+	chain, err := ToolchainFor("typescript")
+	if err != nil {
+		t.Fatalf("typescript is not buildable: %v", err)
+	}
+	if chain.Base == "" || chain.Artifact == "" {
+		t.Fatalf("a toolchain names no base to compile in: %+v", chain)
+	}
+	if len(chain.Compile) == 0 || chain.Output == "" {
+		t.Fatalf("a toolchain says nothing about how to compile or where output lands: %+v", chain)
+	}
+}
+
+// Case and stray whitespace are a module author's slip, not a different language.
+func TestALanguageIsMatchedLoosely(t *testing.T) {
+	for _, said := range []string{"TypeScript", " typescript ", "TYPESCRIPT"} {
+		if _, err := ToolchainFor(said); err != nil {
+			t.Fatalf("%q was refused: %v", said, err)
+		}
+	}
+}
+
+// **A refusal says what would have worked.** A module author who names a language the mesh does
+// not build is one word away from a language it does, and a bare "unsupported" makes them go
+// looking for a list that exists in one place in the source.
+func TestAnUnknownLanguageSaysWhatIsBuildable(t *testing.T) {
+	_, err := ToolchainFor("cobol")
+	if err == nil {
+		t.Fatal("a language nothing can build was accepted")
+	}
+	for _, want := range Languages() {
+		if !strings.Contains(err.Error(), want) {
+			t.Fatalf("the refusal does not mention %q, which would have worked: %v", want, err)
+		}
+	}
+}
+
+// And saying nothing is its own message: the mesh chooses the compiler, so a bundle that names no
+// language has not asked for anything in particular — which is a mistake rather than a default.
+func TestABundleMustSayWhatItIsWrittenIn(t *testing.T) {
+	_, err := ToolchainFor("")
+	if err == nil {
+		t.Fatal("a bundle with no language was accepted, so the mesh guessed a compiler")
+	}
+	if !strings.Contains(err.Error(), "must say") {
+		t.Fatalf("the refusal does not say a language is required: %v", err)
+	}
+}
diff --git a/internal/catalogue/build.go b/internal/catalogue/build.go
index 361c65e..d7df29a 100644
--- a/internal/catalogue/build.go
+++ b/internal/catalogue/build.go
@@ -88,12 +88,16 @@ func (m Manifest) Resolve(built []Built) (Manifest, error) {
 		switch artifact.Kind {
 		case ArtifactImage, ArtifactUpstream:
 			filled["image"] = artifact.Reference
-		case ArtifactArchive:
+		case ArtifactArchive, ArtifactBundle:
+			// The same on the wire: both are bytes fetched by digest and unpacked. They differ in
+			// how they were made — one packed as it stood, the other compiled first — and a
+			// machine has no reason to care which.
 			filled["source"] = artifact.Reference
 			filled["digest"] = artifact.Digest
 		default:
-			return Manifest{}, fmt.Errorf("%s: %q is a %q, and an artifact is %q, %q or %q",
-				m.Module, named, artifact.Kind, ArtifactImage, ArtifactArchive, ArtifactUpstream)
+			return Manifest{}, fmt.Errorf("%s: %q is a %q, and an artifact is %q, %q, %q or %q",
+				m.Module, named, artifact.Kind, ArtifactImage, ArtifactArchive, ArtifactUpstream,
+				ArtifactBundle)
 		}
 		out.Resources = append(out.Resources, filled)
 	}
@@ -119,15 +123,40 @@ func (b *Build) problems(module string) []string {
 		}
 		seen[a.Name] = true
 		switch a.Kind {
-		case ArtifactImage, ArtifactArchive, ArtifactUpstream:
+		case ArtifactImage, ArtifactArchive, ArtifactUpstream, ArtifactBundle:
 		default:
 			problems = append(problems, fmt.Sprintf(
-				"%s: %q is a %q, and an artifact is %q, %q or %q",
-				module, a.Name, a.Kind, ArtifactImage, ArtifactArchive, ArtifactUpstream))
+				"%s: %q is a %q, and an artifact is %q, %q, %q or %q",
+				module, a.Name, a.Kind, ArtifactImage, ArtifactArchive, ArtifactUpstream,
+				ArtifactBundle))
 		}
-		if a.From == "" {
-			problems = append(problems, fmt.Sprintf(
-				"%s: %q says nothing about what it is built from", module, a.Name))
+		// **A bundle is built from the module itself, so it says a language instead.** Everything
+		// else names what it is built from: a Dockerfile, a directory, somebody else's reference.
+		// A bundle's source is the module's own directory by definition, and what it needs to say
+		// is which compiler — because the mesh chooses that, and cannot choose for a module that
+		// has not said.
+		if a.Kind == ArtifactBundle {
+			if a.From != "" {
+				problems = append(problems, fmt.Sprintf(
+					"%s: %q is a bundle and names what it is built from (%q). A bundle is built "+
+						"from the module's own directory; what it says is the language",
+					module, a.Name, a.From))
+			}
+			if strings.TrimSpace(a.Language) == "" {
+				problems = append(problems, fmt.Sprintf(
+					"%s: %q is a bundle and says no language, so nothing can choose a compiler "+
+						"for it", module, a.Name))
+			}
+		} else {
+			if a.From == "" {
+				problems = append(problems, fmt.Sprintf(
+					"%s: %q says nothing about what it is built from", module, a.Name))
+			}
+			if a.Language != "" {
+				problems = append(problems, fmt.Sprintf(
+					"%s: %q is a %q and names a language. Only a bundle is compiled by the mesh; "+
+						"everything else brings its own recipe", module, a.Name, a.Kind))
+			}
 		}
 		// An upstream image is named, not read from the repository, so the path rule does not
 		// apply to it — and applying it anyway would refuse every reference with a registry host
diff --git a/internal/catalogue/manifest.go b/internal/catalogue/manifest.go
index 2085d2d..7f6eb9c 100644
--- a/internal/catalogue/manifest.go
+++ b/internal/catalogue/manifest.go
@@ -389,6 +389,26 @@ type Artifact struct {
 	// version and an operating system — while letting each be built and published separately.
 	// Empty means the whole recipe, which is what a module with one image says by saying nothing.
 	Target string `json:"target,omitempty"`
+
+	// Language is what this module's code is written in, for a bundle.
+	//
+	// **Declared, never guessed.** Inferring it from what files happen to be present makes a
+	// module's build depend on a directory listing, and a module that adds a stray file builds
+	// differently for a reason nobody can see. It is also the only thing a bundle needs to say:
+	// everything else about the toolchain — which compiler, which flags, which base — is the
+	// mesh's, and a module that could override it would be writing a Dockerfile again.
+	//
+	// Empty for every other kind, which do not compile.
+	Language string `json:"language,omitempty"`
+
+	// Entrypoints are the compiled files a tool host should load from this module, relative to the
+	// bundle's root.
+	//
+	// **Named rather than derived from which files exist**, for the same reason as the language:
+	// the module knows what it serves, and a build that guesses would change meaning when
+	// somebody adds a helper. An empty list is a bundle that is run rather than loaded — a
+	// provisioner or a step, named by whatever runs it.
+	Entrypoints []string `json:"entrypoints,omitempty"`
 }
 
 // Kinds an artifact may be.
@@ -397,6 +417,21 @@ const (
 	ArtifactImage = "image"
 	// ArtifactArchive is a directory in this repository, packed.
 	ArtifactArchive = "archive"
+	// ArtifactBundle is this module's own code, COMPILED by a toolchain and then packed.
+	//
+	// **The one recipe that both builds and packs**, and the reason it exists is the authoring
+	// burden. An `archive` packs a directory as it stands, so shipping compiled output means
+	// compiling somewhere first — which means a Dockerfile, repeating the same incantation in
+	// every module: two base arguments, a working directory chosen so the SDK resolves upward, the
+	// compiler invoked by absolute path because the usual symlink is resolved away when the base is
+	// assembled, a second stage, an environment variable naming the entrypoints. Most of the
+	// catalogue is unconverted and that is why.
+	//
+	// A bundle says what the module is written in and nothing about how. The mesh knows what a
+	// language implies, which is the whole of the difference: a Dockerfile is right for software
+	// that needs a particular base, and wrong for "compile my module's code", which is the same
+	// operation every time.
+	ArtifactBundle = "bundle"
 	// ArtifactUpstream is an image somebody else built, mirrored into the mesh's own registry and
 	// pinned by the digest it lands with.
 	//