Anchor dependency preparation to checkout root

preparation.go

@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"strings"
 
+	"go.maximumdirect.net/releasekit/internal/git"
 	internalpreparation "go.maximumdirect.net/releasekit/internal/preparation"
 	"go.maximumdirect.net/releasekit/internal/releaseidentity"
 )
@@ -37,11 +38,13 @@ func PrepareTaggedCheckout(ctx context.Context, request TaggedCheckoutRequest) e
 }
 
 // DependencyPreparationRequest selects the repository module whose dependencies
-// should be prepared.
+// should be prepared. Within a checkout, RepositoryDir may name any directory
+// in it; ModuleDir is resolved from the checkout root. Outside a checkout,
+// ModuleDir is resolved from RepositoryDir.
 type DependencyPreparationRequest struct {
 	RepositoryDir string
-	// ModuleDir selects a repository-relative module directory; empty selects
-	// the repository root.
+	// ModuleDir selects a directory relative to the checkout root or standalone
+	// RepositoryDir; empty selects that base.
 	ModuleDir string
 }
 
@@ -55,7 +58,15 @@ func PrepareBuildDependencies(ctx context.Context, request DependencyPreparation
 	if strings.TrimSpace(request.RepositoryDir) == "" {
 		return errors.New("repository directory is required")
 	}
-	selection, err := releaseidentity.ResolveSelection(request.RepositoryDir, request.ModuleDir)
+	base := request.RepositoryDir
+	root, found, err := git.DiscoverRepositoryRoot(ctx, base)
+	if err != nil {
+		return fmt.Errorf("discover dependency preparation repository: %w", err)
+	}
+	if found {
+		base = root
+	}
+	selection, err := releaseidentity.ResolveSelection(base, request.ModuleDir)
 	if err != nil {
 		return fmt.Errorf("resolve dependency preparation module: %w", err)
 	}