Add artifact workdir layout and locking

internal/app/plan.go

@@ -6,10 +6,11 @@ import (
 	"fmt"
 	"io"
 
+	"gitea.maximumdirect.net/eric/narratio/internal/artifacts"
 	"gitea.maximumdirect.net/eric/narratio/internal/config"
 )
 
-// Plan validates configuration inputs and reports readiness for future planning.
+// Plan validates configuration inputs and prepares the local session workdir.
 func Plan(_ context.Context, args []string, out io.Writer) error {
 	fs := flag.NewFlagSet("plan", flag.ContinueOnError)
 	fs.SetOutput(io.Discard)
@@ -37,6 +38,12 @@ func Plan(_ context.Context, args []string, out io.Writer) error {
 		return fmt.Errorf("plan: %w", err)
 	}
 
-	_, err = fmt.Fprintln(out, "narratio plan: configuration loaded and valid")
+	store := artifacts.NewLocalStore(cfg.Pipeline.Workspace.Root)
+	paths, err := store.EnsureLayout(cfg.Session.SessionID)
+	if err != nil {
+		return fmt.Errorf("plan: prepare workdir: %w", err)
+	}
+
+	_, err = fmt.Fprintf(out, "narratio plan: configuration loaded and valid; workdir prepared at %s\n", paths.Root)
 	return err
 }