Chat: page back through Global history (#472)

ddiff --git a/public/web/chat.js b/public/web/chat.js
iindex 6c7743f..80f028b 100644
---- a/public/web/chat.js
++++ b/public/web/chat.js
@@@ -235,6 +235,29 @@
    function startGlobal() {
      var live = document.getElementById('oc-live');
      var ws = null, delay = 1000, opened = false;
++    var historyState = document.getElementById('oc-history-state'), loadingEarlier = false, historyMore = true;
++    function loadEarlier() {
++      if (loadingEarlier || !historyMore || !feed) return;
++      var first = feed.querySelector('[data-id]');
++      if (!first) return;
++      loadingEarlier = true;
++      if (historyState) historyState.textContent = 'Loading earlier messages';
++      var before = Number(first.dataset.id), height = feed.scrollHeight, top = feed.scrollTop;
++      fetch('/api/chat/global/history?before=' + encodeURIComponent(before) + '&limit=50', { credentials: 'same-origin' })
++        .then(function (r) { return r.ok ? r.json() : null; })
++        .then(function (d) {
++          if (!d || !Array.isArray(d.messages)) return;
++          var anchor = feed.querySelector('[data-id="' + first.dataset.id + '"]');
++          (d.messages || []).forEach(function (m) {
++            if ((m.message_type || 'chat') === 'chat' && !m.is_deleted && !feed.querySelector('[data-id="' + m.id + '"]')) feed.insertBefore(globalItem(m), historyState && historyState.nextSibling);
++          });
++          historyMore = !!d.more;
++          if (historyState) historyState.textContent = historyMore ? '' : 'The start of the chat';
++          if (anchor) feed.scrollTop = top + (feed.scrollHeight - height);
++        }).catch(function () {}).finally(function () { loadingEarlier = false; });
++    }
++    if (feed) feed.addEventListener('scroll', function () { if (feed.scrollTop < 600) loadEarlier(); });
++    if (feed) { feed.scrollTop = feed.scrollHeight; }
      // A workspace room's queue (server/web/workspace-pages.js): its panel reloads when the socket says it changed.
      var queueBox = document.getElementById('oc-queue'), queueTimer = null;
      function refreshQueue() {
ddiff --git a/server/chat/history-store.js b/server/chat/history-store.js
iindex 4921761..17fbb82 100644
---- a/server/chat/history-store.js
++++ b/server/chat/history-store.js
@@@ -3,7 +3,7 @@
   *
   * Rooms:  'global' | 'channel:<userId>'        (the stream route keeps its own scope logic)
   * Reads:
-- *   page(room, { limit, before })      newest `limit` rows, oldest→newest — the first paint
++ *   page(room, { limit, before })      newest `limit` rows, newest→oldest — the first paint
   *   delta(room, { afterId, limit })    rows with id > afterId, oldest→newest — reopen, reconnect,
   *                                      tab focus. Cheap: a primary-key range scan, no reverse.
   *                                      Plus `deleted_ids` (deletedIds below): the rows at or under
@@@ -98,11 +98,12 @@ function memoSet(key, value) {
  async function readPage(r, { limit, before, channelUsername }) {
      const { sql, params } = baseSql(r, { channelUsername });
      let q = sql;
--    if (before) { q += ' AND cm.timestamp < ?'; params.push(before); }
++    if (before) { q += ' AND cm.id < ?'; params.push(before); }
      // The page order is the primary key alone (plan T3 decision 2): ids are monotonic in insert order,
      // so this is the same order as before, and idx_chat_page_live serves it without a sort on PostgreSQL.
--    q += ' ORDER BY cm.id DESC LIMIT ?'; params.push(limit);
--    return (await db.all(q, params)).reverse();
++    q += ' ORDER BY cm.id DESC LIMIT ?'; params.push(limit + 1);
++    const rows = await db.all(q, params);
++    return { rows: rows.slice(0, limit), more: rows.length > limit };
  }
  
  async function readDelta(r, { afterId, limit, channelUsername }) {
@@@ -114,8 +115,8 @@ async function readDelta(r, { afterId, limit, channelUsername }) {
  }
  
  /**
-- * Newest rows of a room, oldest→newest.
-- * @returns {{ messages: object[], latest_id: number }}
++ * Newest rows of a room, newest→oldest. `before` is an exclusive message id cursor.
++ * @returns {{ messages: object[], latest_id: number, more: boolean }}
   */
  async function page(room, { limit, before, channelUsername, decorate } = {}) {
      const r = parseRoom(room);
@@@ -123,15 +124,16 @@ async function page(room, { limit, before, channelUsername, decorate } = {}) {
      // The newest row id is part of the memo key, so a memoised page can never miss a message:
      // one primary-key lookup instead of the five-table join for every repeat reader in the window.
      const key = !before ? `${room}|${lim}|${channelUsername || ''}|${await tipId()}` : null;
--    let rows = key ? memoGet(key) : null;
--    if (!rows) {
--        rows = await readPage(r, { limit: lim, before, channelUsername });
--        if (key) memoSet(key, rows);
++    let page = key ? memoGet(key) : null;
++    if (!page) {
++        page = await readPage(r, { limit: lim, before, channelUsername });
++        if (key) memoSet(key, page);
      }
      // Copies: the page memo holds the rows, and a refreshed card must not change what the next reader sees.
++    const rows = page.rows;
      const messages = decorate ? decorate(rows.map((x) => ({ ...x }))) : rows.map((x) => ({ ...x }));
      await linkCards.hydrate(messages, 'chat_messages');
--    return { messages, latest_id: latestIdOf(rows) };
++    return { messages, latest_id: latestIdOf(rows), more: page.more };
  }
  
  /**
ddiff --git a/server/chat/routes.js b/server/chat/routes.js
iindex a3d5beb..f40a660 100644
---- a/server/chat/routes.js
++++ b/server/chat/routes.js
@@@ -518,12 +518,13 @@ router.get('/filters/friendly', (req, res) => {
  
  router.get('/global/history', optionalAuth, async (req, res) => {
      try {
--        const limit = req.query.limit;
++        const askedLimit = parseInt(req.query.limit, 10);
++        const limit = Math.min(Number.isFinite(askedLimit) && askedLimit > 0 ? askedLimit : 50, 100);
          const before = req.query.before;
          const afterId = req.query.after_id;
          const channelUsername = String(req.query.username || '').trim();
          // after_id = cursor read: only what the caller has not seen (oldest→newest, PK range scan).
--        // Anything else = a page: the newest rows, optionally before a timestamp.
++        // Anything else = a page: the newest rows, optionally before an exclusive message id.
          const out = afterId != null
              ? await historyStore.delta('global', { afterId, limit, channelUsername })
              : await historyStore.page('global', { limit, before, channelUsername });
ddiff --git a/server/web/pages.js b/server/web/pages.js
iindex ecf7f9d..d4e0c30 100644
---- a/server/web/pages.js
++++ b/server/web/pages.js
@@@ -251,7 +251,7 @@ function createWebRoutes({ config }) {
      // ── Global chat ──
      router.get('/', async (req, res) => {
          const actor = await viewerOf(req);
--        const { messages, latest_id } = await historyStore.page('global', { limit: 60 });
++        const { messages, latest_id } = await historyStore.page('global', { limit: 50 });
          // Not the lines of people this reader blocked on the network (chat/network-blocks.js).
          const hidden = actor.kind === 'user' ? await require('../chat/network-blocks').blockedUserIds(actor.user) : new Set();
          // And not what OpenVibe's global room does not show of other rooms' lines (chat/global-standard.js).
@@@ -295,7 +295,7 @@ function createWebRoutes({ config }) {
          ].filter((pane) => pane.html);
          const explore = pickBlock({ key: 'explore', label: 'Explore OpenVibe.Chat', head: 'Explore OpenVibe.Chat', panes });
          const inlineStyles = [];
--        const feedList = `<ol class="oc-feed${signedIn ? ' oc-srv-feed' : ''}" id="oc-feed" aria-live="polite" aria-label="Messages">${shown.map(globalMessage).join('\n') || '<li class="oc-empty oc-muted">No messages yet. Say hello.</li>'}</ol>`;
++        const feedList = `<ol class="oc-feed${signedIn ? ' oc-srv-feed' : ''}" id="oc-feed" aria-live="polite" aria-label="Messages"><li id="oc-history-state" class="oc-muted" aria-live="polite"></li>${shown.slice().reverse().map(globalMessage).join('\n') || '<li class="oc-empty oc-muted">No messages yet. Say hello.</li>'}</ol>`;
          // Someone signed in gets the app shell (the plan, 2026-11-09, stage V2): Global chat is a destination on the
          // rail, the side column is Home's, and the feed fills the middle with the composer at its foot.
          const shellBody = signedIn ? await (async () => {
ddiff --git a/test/rest.test.js b/test/rest.test.js
iindex 092db8d..43f824f 100644
---- a/test/rest.test.js
++++ b/test/rest.test.js
@@@ -118,8 +118,14 @@ t('chat history: global page and cursor delta, deleted and expired rows hidden',
      await h.db.run("UPDATE chat_messages SET auto_delete_at = '2000-01-01 00:00:00' WHERE id = ?", [ids[2]]);
      const page = await h.http('GET', '/api/chat/global/history?limit=10');
      const got = page.body.messages.map((m) => m.message);
--    assert.deepStrictEqual(got.filter((x) => /^g\d$/.test(x)), ['g0', 'g3', 'g4']);
++    assert.deepStrictEqual(got.filter((x) => /^g\d$/.test(x)), ['g4', 'g3', 'g0']);
      assert.strictEqual(page.body.latest_id, ids[4]);
++    const firstPage = await h.http('GET', '/api/chat/global/history?limit=2');
++    assert.strictEqual(firstPage.body.more, true);
++    assert.deepStrictEqual(firstPage.body.messages.map((m) => m.id), [ids[4], ids[3]]);
++    const older = await h.http('GET', `/api/chat/global/history?before=${ids[3]}&limit=2`);
++    assert.strictEqual(older.body.more, false);
++    assert.deepStrictEqual(older.body.messages.map((m) => m.id).filter((id) => ids.includes(id)), [ids[0]]);
      const delta = await h.http('GET', `/api/chat/global/history?after_id=${ids[3]}`);
      assert.deepStrictEqual(delta.body.messages.map((m) => m.message), ['g4']);
      assert.strictEqual(delta.body.complete, true);