Bugfix involving nested directory creation

internal/stage/run_local.go

@@ -99,7 +99,11 @@ func runLocalPathForCanonical(layout runStageLayout, sessionPaths artifacts.Sess
 	if rel == "." || rel == ".." || strings.HasPrefix(rel, ".."+string(filepath.Separator)) {
 		return "", fmt.Errorf("canonical path %q is outside session root %q", cleanCanonical, sessionPaths.Root)
 	}
-	return filepath.Join(layout.OutputsDir, rel), nil
+	localPath := filepath.Join(layout.OutputsDir, rel)
+	if err := os.MkdirAll(filepath.Dir(localPath), 0o755); err != nil {
+		return "", fmt.Errorf("create run-local output parent for %q: %w", localPath, err)
+	}
+	return localPath, nil
 }
 
 func promoteRunLocalOutput(

internal/stage/run_local_test.go

@@ -0,0 +1,35 @@
+package stage
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+
+	"gitea.maximumdirect.net/eric/narratio/internal/artifacts"
+)
+
+func TestRunLocalPathForCanonicalCreatesParentDirectories(t *testing.T) {
+	root := t.TempDir()
+	sessionRoot := filepath.Join(root, "work", "dilfs", "2026-05-17")
+	layout := runStageLayout{
+		Enabled:    true,
+		OutputsDir: filepath.Join(sessionRoot, "runs", "run-1", "merge", "outputs"),
+	}
+	if err := os.MkdirAll(layout.OutputsDir, 0o755); err != nil {
+		t.Fatalf("mkdir outputs dir: %v", err)
+	}
+
+	canonical := filepath.Join(sessionRoot, "transcripts", "merged.json")
+	got, err := runLocalPathForCanonical(layout, artifacts.SessionPaths{Root: sessionRoot}, canonical)
+	if err != nil {
+		t.Fatalf("runLocalPathForCanonical() error = %v", err)
+	}
+
+	want := filepath.Join(layout.OutputsDir, "transcripts", "merged.json")
+	if got != want {
+		t.Fatalf("runLocalPathForCanonical() = %q, want %q", got, want)
+	}
+	if _, err := os.Stat(filepath.Dir(got)); err != nil {
+		t.Fatalf("expected run-local parent directory to exist: %v", err)
+	}
+}