Move the Go build source reader out of internal/builder so the builder can go (issue 1851, C1a)

internal/builder/builder.go

@@ -9,6 +9,7 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
+	"github.com/novox/mesh-controller/internal/gosource"
 	"io"
 	"io/fs"
 	"os"
@@ -1207,13 +1208,13 @@ func one(ctx context.Context, run Runner, publish Publisher,
 		// merge elsewhere in that repository is no change to it — and a recipe that copies a file outside
 		// it fails here, naming the file, rather than building from something no merge is mapped onto.
 		if a.Compiles != "" {
-			paths, err := GoBuildSource(buildDir, a.Compiles)
+			paths, err := gosource.GoBuildSource(buildDir, a.Compiles)
 			if err != nil {
 				return catalogue.Built{}, fmt.Errorf("%s: %s compiles %s, whose build source cannot be read: %w",
 					module, a.Name, a.Compiles, err)
 			}
 			narrowed := filepath.Join(workspace, "narrow-"+a.Name)
-			sum, err := narrowTree(buildDir, narrowed, paths)
+			sum, err := gosource.NarrowTree(buildDir, narrowed, paths)
 			if err != nil {
 				return catalogue.Built{}, fmt.Errorf("%s: handing %s its build source: %w", module, a.Name, err)
 			}
@@ -1311,7 +1312,7 @@ func one(ctx context.Context, run Runner, publish Publisher,
 		// A Go program's build source is its import closure (novox/hq ADR 0267 rule 1). Not read, it is the
 		// module's whole directory, as before — said, so the wider plan has a reason a person can find.
 		if chain.Language == "go" {
-			if paths, err := GoBuildSource(tree, a.From); err != nil {
+			if paths, err := gosource.GoBuildSource(tree, a.From); err != nil {
 				say("bundle", "%s's build source is its whole directory: %v", a.Name, err)
 				src.ownWhole()
 			} else {