mesh-build-node: narrow the fetch to the named paths, build members against the SDK their lock names, and build, pack and publish a package (issues 1758, 1587 S15-S19; ADR 0499 §4, ADR 0498 §5, ADR 0500 §4-§6; lead decision L10)

build_node_fetch takes buildstep.FetchRequest (dir and paths narrow the workspace) and an
optional package {repository, commit, ref}: the group's package member, built and packed
shut off and published nowhere. Each member's lock decides its SDK: the group's packed
file when the version and integrity are the lock's, else the registry's (integrity
checked); a version the registry lacks fails waits for: @novox/mesh-sdk@<version>. A
package artifact is built by its own script and packed with npm pack, shut off; only a
trunk build publishes it, from this process with the write credential (never in a
workspace): absent is published, the same file is done, another is version taken:. The
registry configuration file now lies outside every workspace.

modules/mesh-build-node/cmd/mesh-build-node/build.go

@@ -36,6 +36,7 @@ type artifact struct {
 	// module is the manifest's module name, which the artifact is stored under.
 	module      string
 	Name        string   `json:"name"`
+	Kind        string   `json:"kind"`
 	Language    string   `json:"language"`
 	Entrypoints []string `json:"entrypoints"`
 	External    []string `json:"external"`
@@ -89,6 +90,9 @@ func (m *Module) build(ctx context.Context, args map[string]any) (any, error) {
 	if err != nil {
 		return nil, err
 	}
+	if a.Kind == "package" {
+		return m.buildPackage(ctx, workspace, module, root, dir, a, publish)
+	}
 	if why, err := lockProblem(dir, module); err != nil || why != "" {
 		if err == nil {
 			err = fmt.Errorf("%s was refused by the fetch: %s", name, why)
@@ -280,6 +284,10 @@ func readArtifact(dir, name string) (artifact, error) {
 		if a.Name != name {
 			continue
 		}
+		if a.Kind == "package" && a.Language == "typescript" {
+			a.module = m.Module
+			return a, nil // a package is built by its own build script and packed (package.go), from no entrypoint
+		}
 		if a.Language != "typescript" {
 			return artifact{}, fmt.Errorf("artifact %q is %q, and this module builds typescript", name, a.Language)
 		}