feat(packages): ludic.save - versioned save files generic over their content: a version in the file, the steps a game declares into an open registry, a torn write told from a whole one, a backup of only a whole file, a write read back, a newer file refused and read-only

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

packages/ludic.save/write.ludic

@@ -0,0 +1,16 @@
+# write.ludic - a write that is known to be on disk: the old file to the backup first (only when it
+# is whole - a torn file must never replace a good backup), then the new text, read straight back
+# and compared, because a caller about to delete something on the strength of it needs to know
+export function save_write(path: string, backup: string, text: string) -> bool {
+  let old = Fs.read_text(path)
+  if old != null and len(backup) > 0 and save_text_intact(old) { Fs.write_text(backup, old) }
+  Fs.write_text(path, text)
+  let back = Fs.read_text(path)
+  return back != null and back == text
+}
+
+# a SaveRead that must not be written over says so; a write through it refuses
+export function save_write_to(r: SaveRead, path: string, backup: string, text: string) -> bool {
+  if r != null and r.readonly { return false }
+  return save_write(path, backup, text)
+}