DM notifications link to /?dm=<conversation id>, which the messenger opens once someone is signed in (and drops from the address bar). They used to link to /dm/<id>, a page Live never had: it showed the home page and, since real 404s, Page not found. Links already sent redirect from /dm/<id>

ddiff --git a/public/js/messenger.js b/public/js/messenger.js
iindex eec4f228..01430399 100644
---- a/public/js/messenger.js
++++ b/public/js/messenger.js
@@@ -1193,6 +1193,27 @@
          // Hook into chat WebSocket message handler
          // The chat.js `handleChatMessage` will call `handleIncomingDm` for DM type messages
          window._messengerHandleDm = handleIncomingDm;
++        openLinkedThread();
++    }
++
++    // DM notifications (Network push, the notification centre) link to /?dm=<conversation id>:
++    // open that thread once someone is signed in, and take the parameter out of the address bar.
++    function openLinkedThread() {
++        const params = new URLSearchParams(location.search);
++        if (!params.has('dm')) return;
++        const id = Number(params.get('dm'));
++        params.delete('dm');
++        const qs = params.toString();
++        history.replaceState(history.state, '', location.pathname + (qs ? `?${qs}` : '') + location.hash);
++        if (!Number.isSafeInteger(id) || id <= 0) return;
++        const open = () => { if (!panelOpen) togglePanel(); openThread(id); };
++        if (typeof currentUser !== 'undefined' && currentUser) return open();
++        const onAuth = (e) => {
++            if (!e.detail || !e.detail.user) return;
++            window.removeEventListener('openvibe-auth-changed', onAuth);
++            open();
++        };
++        window.addEventListener('openvibe-auth-changed', onAuth);
      }
  
      function resetMessengerStateForAuthChange(newUser) {
ddiff --git a/server/chat/dm-routes.js b/server/chat/dm-routes.js
iindex d258e19f..79f9c7aa 100644
---- a/server/chat/dm-routes.js
++++ b/server/chat/dm-routes.js
@@@ -217,7 +217,7 @@ router.post('/conversations/:id/messages', (req, res) => {
                      type: 'DIRECT_MESSAGE',
                      title: `Message from ${senderName}`,
                      message: preview,
--                    url: `https://openvibe.live/dm/${convId}`,
++                    url: `https://openvibe.live/?dm=${convId}`,
                      ...actorInfo(sender),
                  });
              }
ddiff --git a/server/chat/live-context-routes.js b/server/chat/live-context-routes.js
iindex f3f80cb1..dbb6d79c 100644
---- a/server/chat/live-context-routes.js
++++ b/server/chat/live-context-routes.js
@@@ -564,7 +564,7 @@ effectsRouter.post('/notify/dm', (req, res) => {
                  type: 'DIRECT_MESSAGE',
                  title: `Message from ${senderName}`,
                  message: 'Sent you a message',
--                url: `https://openvibe.live/dm/${convId}`,
++                url: `https://openvibe.live/?dm=${convId}`,
                  ...actorInfo(sender),
              });
          }
ddiff --git a/server/index.js b/server/index.js
iindex 9cfd5bca..fde65872 100644
---- a/server/index.js
++++ b/server/index.js
@@@ -886,6 +886,10 @@ app.get('/media/:username', (req, res) => {
      sendDocument(res, 'media-player.html');
  });
  
++// DM notifications sent before 2026-09-23 linked to /dm/<conversation id>, a page Live never had;
++// the messenger opens the thread from /?dm=<id> now.
++app.get(/^\/dm\/(\d{1,12})\/?$/, (req, res) => res.redirect(302, `/?dm=${req.params[0]}`));
++
  // ── Legal Pages ───────────────────────────────────────────────
  app.get('/dmca', (req, res) => {
      sendDocument(res, 'dmca.html');