Add previous-session workspace path helpers and layout support

internal/stage/run_local.go

@@ -7,6 +7,7 @@ import (
 	"strings"
 
 	"gitea.maximumdirect.net/eric/narratio/internal/artifacts"
+	"gitea.maximumdirect.net/eric/narratio/internal/config"
 	"gitea.maximumdirect.net/eric/narratio/internal/manifest"
 )
 
@@ -99,6 +100,9 @@ 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)
 	}
+	if rel == config.PathPreviousDirSegment || strings.HasPrefix(rel, config.PathPreviousDirSegment+string(filepath.Separator)) {
+		return cleanCanonical, 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)

internal/stage/run_local_test.go

@@ -33,3 +33,24 @@ func TestRunLocalPathForCanonicalCreatesParentDirectories(t *testing.T) {
 		t.Fatalf("expected run-local parent directory to exist: %v", err)
 	}
 }
+
+func TestRunLocalPathForCanonicalKeepsPreviousStateSessionDurable(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", "prepare", "outputs"),
+	}
+	if err := os.MkdirAll(layout.OutputsDir, 0o755); err != nil {
+		t.Fatalf("mkdir outputs dir: %v", err)
+	}
+
+	canonical := filepath.Join(sessionRoot, "previous", "artifacts", "session_recap.md")
+	got, err := runLocalPathForCanonical(layout, artifacts.SessionPaths{Root: sessionRoot}, canonical)
+	if err != nil {
+		t.Fatalf("runLocalPathForCanonical() error = %v", err)
+	}
+	if got != canonical {
+		t.Fatalf("runLocalPathForCanonical() = %q, want canonical %q", got, canonical)
+	}
+}