Milestones: a recorded mark stays done whatever its stamp

The done-check read the stored value, so a mark recorded as 0 counted as never
celebrated. Seeding the already-passed hundreds that way would have made the
site announce "400 members" to a channel watching 528. It now tests that the
mark is present at all. Caught before it posted; the live state has been
re-stamped either way.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

snapshot.js

@@ -153,7 +153,9 @@ async function milestoneTick() {
   const sc = X.siteConfig(); if (!sc.telegramBotToken) return null;
   const st = state(); const done = st.milestones || {};
   const count = await memberCount();
-  const due = marksUpTo(count).filter(m => !done[m]);
+  // presence of the key is what counts, never its value: a mark recorded as 0 (or any other
+  // falsy stamp) must stay done, or the ladder back-posts a number the site passed long ago
+  const due = marksUpTo(count).filter(m => !Object.prototype.hasOwnProperty.call(done, m));
   if (!due.length) return null;
   const mark = due[due.length - 1];
   const text = composeMilestone(mark, await gather(), sc.telegramCtaUrl);