pruneOldSelections function
Deletes sel-* files older than maxAge from refDir — each tap
leaves a .json+.png pair behind, and nobody's going back to
reference a selection from an hour ago.
Implementation
void pruneOldSelections(Directory refDir, {Duration maxAge = const Duration(hours: 1)}) {
if (!refDir.existsSync()) return;
final DateTime cutoff = DateTime.now().subtract(maxAge);
for (final FileSystemEntity entity in refDir.listSync()) {
if (entity is! File) continue;
final String name = entity.uri.pathSegments.last;
if (!name.startsWith('sel-')) continue;
if (entity.statSync().modified.isBefore(cutoff)) {
entity.deleteSync();
}
}
}