Graphics debug log: also log what is drawn, optionally to a file

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019reK4DUGYqDUjniWYJvwUW

internal/ui/app.go

@@ -197,7 +197,22 @@ func New(cfg *config.Config) *App {
 // helps to find out why a poster is drawn wrongly in some terminal.
 func (a *App) newGraphics() *kittyGraphics {
 	k := newKittyGraphics(a.writeTerminal)
-	if os.Getenv("ARR_TUI_DEBUG_GFX") != "" {
+	switch v := os.Getenv("ARR_TUI_DEBUG_GFX"); {
+	case v == "":
+	case strings.Contains(v, "/"):
+		// A path: also append to that file, so the lines can be read without
+		// leaving the view that shows the problem.
+		f, err := os.OpenFile(v, os.O_CREATE|os.O_WRONLY|os.O_APPEND, 0o600)
+		if err != nil {
+			a.logs.add(levelWarn, "ARR_TUI_DEBUG_GFX: "+err.Error())
+			k.debug = func(msg string) { a.logs.add(levelInfo, msg) }
+			break
+		}
+		k.debug = func(msg string) {
+			a.logs.add(levelInfo, msg)
+			fmt.Fprintf(f, "%s %s\n", time.Now().Format("15:04:05.000"), msg)
+		}
+	default:
 		k.debug = func(msg string) { a.logs.add(levelInfo, msg) }
 	}
 	return k