Remove unnecessary output restrictions and simplify report tests

internal/core/diagnostics/output_session.go

@@ -16,11 +16,13 @@ const (
 
 // OutputSelection contains only active destinations. ProtectedPaths are inputs
 // and loaded configuration/profile sources that must never be overwritten.
+// InputTranscriptPath may be replaced by final transcript publication, but not reports.
 type OutputSelection struct {
-	TranscriptPath   string
-	ReportDir        string
-	ReportingEnabled bool
-	ProtectedPaths   []string
+	InputTranscriptPath string
+	TranscriptPath      string
+	ReportDir           string
+	ReportingEnabled    bool
+	ProtectedPaths      []string
 }
 
 type ReportBundle struct {
@@ -88,7 +90,11 @@ func PrepareOutput(selection OutputSelection) (*OutputSession, error) {
 				return nil, fmt.Errorf("report output %q: %w", path, err)
 			}
 		}
-		for _, source := range protected {
+		sources := protected
+		if path != session.transcript && selection.InputTranscriptPath != "" {
+			sources = append(append([]string(nil), protected...), selection.InputTranscriptPath)
+		}
+		for _, source := range sources {
 			collision, err := sameDestination(path, source)
 			if err != nil {
 				return nil, err
@@ -157,7 +163,7 @@ func (s *OutputSession) Finalize(transcript []byte, reports ReportBundle, failed
 	}
 	failures := make([]FileFailure, 0)
 	if transcript != nil && s.transcript != "" {
-		if err := s.replace(s.transcript, transcript); err != nil {
+		if err := s.writeTranscript(transcript); err != nil {
 			failures = append(failures, FileFailure{Path: s.transcript, Kind: "transcript write", Err: err})
 		}
 	}
@@ -176,6 +182,24 @@ func (s *OutputSession) Finalize(transcript []byte, reports ReportBundle, failed
 	return failures
 }
 
+// Stream destinations use ordinary writes; replacing their directory entry would
+// destroy the device or pipe. Regular files retain per-file replacement.
+func (s *OutputSession) writeTranscript(payload []byte) error {
+	info, err := os.Stat(s.transcript)
+	if err != nil && !errors.Is(err, os.ErrNotExist) {
+		return err
+	}
+	if err == nil && !info.Mode().IsRegular() {
+		file, err := os.OpenFile(s.transcript, os.O_WRONLY, 0)
+		if err != nil {
+			return err
+		}
+		_, writeErr := file.Write(payload)
+		return errors.Join(writeErr, file.Close())
+	}
+	return s.replace(s.transcript, payload)
+}
+
 func bundleParts(bundle ReportBundle) [3][]byte {
 	return [3][]byte{bundle.Errors, bundle.Recoveries, bundle.Markdown}
 }
@@ -183,8 +207,12 @@ func bundleParts(bundle ReportBundle) [3][]byte {
 func preflightTranscript(path string) error {
 	info, err := os.Stat(path)
 	if err == nil {
+		if info.IsDir() {
+			return fmt.Errorf("transcript output %q is a directory", path)
+		}
 		if !info.Mode().IsRegular() {
-			return fmt.Errorf("transcript output %q is not a regular file", path)
+			// Opening a pipe here can block before its reader is ready.
+			return nil
 		}
 		file, openErr := os.OpenFile(path, os.O_WRONLY, 0)
 		if openErr != nil {