The mesh can compile Go, which is why nothing delivered the host

novox/hq 04-ISSUES/142, and ADR 0141's own progressive insight naming
this as the first of two things missing: "nothing can compile it". The
toolchain list was a closed set of typescript and python, whose warning —
every language is another implementation of the contracts modules share —
does not attach to Go. Go is how the host, the control plane and the
builder are written, and none of them is a module in that sense: the host
is what APPLIES modules.

The toolchain names mesh-tools-go as its base rather than pinning an
upstream release here (ADR 0142, 0044): named and not pinned means the
mesh answers with the copy it holds, and moving compiler is a build
instead of an edit to this file.

Two things beyond the list also assumed one language, and both would have
failed after the entry was added:

  sourcesFor turned every entrypoint into a `.ts` file. The extension is
  the toolchain's now — one language's file extension written into the
  code that serves every language is a wall the next one hits.

  The output directory was the compiler's to create. tsc --outDir makes
  one; go build -o writes into a directory and does not make it, failing
  with a message about a path rather than about a build. Made here for
  every toolchain, because which compilers are forgiving is not something
  a reader should have to know.

And a toolchain now says what it is pointed at: a file list from the
module's entrypoints, or the one package the artifact is built `from`.
Pointing `go build` at a file list builds a program out of exactly those
files and ignores the rest of the package — a missing symbol rather than a
legible refusal.

Static and -trimpath: what a machine holds is a file, not a container, so
a binary needing a libc it did not bring is a delivery that works until a
machine differs; and a version comes from where a component sits rather
than from its linker, so two builds of one commit are the same bytes.

internal/builder/toolchain.go

@@ -35,8 +35,30 @@ type Toolchain struct {
 	Compile []string
 	// OutputFlag is how this compiler is told where to put its output.
 	OutputFlag string
+	// Unit is what this compiler is pointed at: UnitSources, the entrypoint files the module named,
+	// or UnitPackage, the one directory the artifact is built `from`.
+	//
+	// **The difference is the language and not the module.** A TypeScript bundle is a set of files
+	// compiled into a set of files, so what to compile is the module's entrypoints with their source
+	// extension. A Go bundle is a package compiled into one binary, and there is no per-file
+	// compilation to name — pointing `go build` at a file list builds a program out of exactly those
+	// files and ignores the rest of the package, which fails as a missing symbol rather than as a
+	// wrong instruction.
+	Unit string
+	// SourceExt is the extension an entrypoint has in the repository, for UnitSources. An entrypoint
+	// is named as it will be FOUND, inside the unpacked bundle, so the source is the same path with
+	// the output directory taken off the front and this on the end.
+	SourceExt string
 }
 
+// What a toolchain is pointed at.
+const (
+	// UnitSources is a list of files, derived from the module's entrypoints.
+	UnitSources = "sources"
+	// UnitPackage is the single directory the artifact is built `from`, compiled whole.
+	UnitPackage = "package"
+)
+
 // Out is where one artifact's compiled output lands, inside the module's own directory.
 //
 // **Per artifact, never per toolchain.** A module is one piece of software and may still be
@@ -71,6 +93,35 @@ var toolchains = []Toolchain{
 			"--target", "ES2022",
 		},
 		OutputFlag: "--outDir",
+		Unit:       UnitSources,
+		SourceExt:  ".ts",
+	},
+	{
+		Language: "go",
+		Base:     "mesh-tools-go",
+		Artifact: "build",
+		// **The mesh's own components, and not modules.** The warning above this list — that every
+		// language is another implementation of the contracts modules share, so adding one commits
+		// to keeping N implementations in step — does not attach here. Go is how the host, the
+		// control plane and the builder are written, and none of them is a module in that sense:
+		// the host is what APPLIES modules. So there is no SDK obligation, and the reason this
+		// entry did not exist was that nothing needed to compile the mesh itself
+		// (novox/hq ADR 0142, and 04-ISSUES/142 where that is why nothing delivers the host).
+		//
+		// Static, because what a machine ends up holding is a file rather than a container, and a
+		// binary that needs a libc it did not bring is a delivery that works until a machine
+		// differs. Trimmed of its own paths for the same reason a version comes from where it sits
+		// rather than from the linker: two builds of one commit produce the same bytes.
+		Compile: []string{
+			"env", "CGO_ENABLED=0", "GOFLAGS=-trimpath",
+			"go", "build", "-ldflags", "-s -w",
+		},
+		OutputFlag: "-o",
+		// Pointed at the package the artifact is built `from`, compiled whole. Go writes the binary
+		// into the output directory, named after the package — so the bundle a machine unpacks is a
+		// directory holding one executable, which is what the delivery mechanism expects
+		// (novox/hq ADR 0141).
+		Unit: UnitPackage,
 	},
 	{
 		Language: "python",
@@ -82,6 +133,8 @@ var toolchains = []Toolchain{
 		// each actually does.
 		Compile:    []string{"python", "-m", "pip", "install", "--no-compile", "--target"},
 		OutputFlag: "",
+		Unit:       UnitSources,
+		SourceExt:  ".py",
 	},
 }