[0.9.1] FORK_IA_UX: Fase 2 cross-device — relay Karvan messages over SSB private msgs

Makes a Karvan room work between two different phones once they're connected to a pub:
- karvan_model: rooms track remoteFeeds (SSB ids of other participants); addRemoteFeed/
  getRemoteFeeds/anyRemoteRooms (feed-id validated, capped at MAX_MEMBERS).
- backend: inviting registers the invitee's feed; joining by link registers the inviter's
  feed (read from the invite PM). Posting a message publishes a private 'karvan-relay' to
  those feeds; an efficient LIVE log-stream subscriber (createLogStream old:false live:true)
  ingests incoming relays and injects them into the local mirror room (dedup by mid,
  skips own → no loop). WebRTC SIGNAL frames are NOT relayed (too many/slow for the log).
- Chosen over a muxrpc plugin because a classic pub only replicates the LOG (store-and-forward);
  live muxrpc wouldn't reach the other phone. No SSB-startup changes → no boot risk.
Verified: boot OK with the live stream, invite/adopt register feeds, message posts + relay
publishes, server stays up, 16/16 tests. Cross-device delivery needs the user's 2-phone+pub test.
Note: text chat only — video still needs the wrapper camera permission (Fase 3).

src/backend/backend.js

@@ -638,6 +638,59 @@ const trendingModel = require('../models/trending_model')({ cooler, isPublic: co
 const statsModel = require('../models/stats_model')({ cooler, isPublic: config.public, tribeCrypto, tribesModel });
 const padsModel = require('../models/pads_model')({ cooler, cipherModel, tribeCrypto, padCrypto, tribesModel });
 const karvanModel = require('../models/karvan_model')({}); // FORK_IA_UX: salas efímeras en RAM (mensajes temporales + señalización WebRTC)
+
+// FORK_IA_UX Fase 2 (cross-device): relay de MENSAJES de Karvan por privados SSB. Funciona vía un pub
+// (el privado se replica al otro móvil); los SIGNAL de WebRTC NO se relayan (serían demasiados/lentos por el log).
+// No toca el arranque del SSB. Ingesta por stream EN VIVO (no polling) → eficiente.
+const karvanSeenRelay = new Set();     // mids ya inyectados (evita duplicados/bucles)
+let karvanRelaySub = false;            // ¿suscriptor del log en vivo montado?
+async function karvanPublishRelay(roomId, mid, from, text) {
+  try {
+    const feeds = karvanModel.getRemoteFeeds(roomId);
+    if (!feeds.length) return;
+    const ssbClient = await cooler.open();
+    const recps = [...new Set([ssbClient.id, ...feeds])].slice(0, 8);
+    await new Promise((res, rej) => ssbClient.private.publish(
+      { type: 'karvan-relay', roomId, mid: String(mid || '').slice(0, 60), from: String(from || '?').slice(0, 80), text: String(text || '').slice(0, 2000), private: true },
+      recps, (e, m) => e ? rej(e) : res(m)));
+  } catch (e) {}
+}
+async function karvanStartRelay() {
+  if (karvanRelaySub) return;
+  karvanRelaySub = true;
+  try {
+    const ssbClient = await cooler.open();
+    const me = ssbClient.id;
+    pull(
+      ssbClient.createLogStream({ old: false, live: true }),
+      pull.drain((m) => {
+        try {
+          if (!m || !m.value) return;
+          let dec; try { dec = ssbClient.private.unbox({ key: m.key, value: m.value, timestamp: m.timestamp }); } catch (_) { return; }
+          const c = dec && dec.value && dec.value.content;
+          if (!c || c.type !== 'karvan-relay' || !c.roomId || !c.mid) return;
+          if (dec.value.author === me) return;               // no reinyectar lo propio (evita bucle A→B→A)
+          if (karvanSeenRelay.has(c.mid)) return;
+          if (!karvanModel.getRoom(c.roomId)) return;        // solo si tenemos esa sala localmente
+          karvanSeenRelay.add(c.mid);
+          if (karvanSeenRelay.size > 5000) karvanSeenRelay.clear();
+          karvanModel.postMessage(c.roomId, { from: c.from, text: c.text, mid: c.mid });
+        } catch (e) {}
+      })
+    );
+  } catch (e) { karvanRelaySub = false; }
+}
+// ¿quién me invitó a esta sala? (para registrar su feed en el espejo local) — reutiliza el lector de privados
+async function karvanInviteAuthor(roomId) {
+  try {
+    const msgs = await pmModel.listAllPrivate();
+    for (const m of (msgs || [])) {
+      const c = m && m.value && m.value.content;
+      if (c && c.subject === 'KARVAN_INVITE' && typeof c.text === 'string' && c.text.indexOf('/karvan/' + roomId) !== -1) return m.value.author;
+    }
+  } catch (e) {}
+  return null;
+}
 const tagsModel = require('../models/tags_model')({ cooler, isPublic: config.public, padsModel, tribesModel });
 const tribesContentModel = require('../models/tribes_content_model')({ cooler, isPublic: config.public, tribeCrypto, tribesModel });
 const searchModel = require('../models/search_model')({ cooler, isPublic: config.public, padsModel, tribeCrypto, tribesModel });
@@ -3658,11 +3711,16 @@ router
     // unirse por enlace/invitación crea un espejo local, pero SOLO en una navegación real (documento):
     // un <img>/subrecurso de una web maliciosa NO debe poder crear/expulsar salas por GET (CSRF). El navegador
     // controla sec-fetch-dest/accept, así que son señales fiables.
+    let justAdopted = false;
     if (!room) {
       const isNav = ctx.get('sec-fetch-dest') === 'document' || (ctx.get('accept') || '').includes('text/html');
-      if (isNav) room = karvanModel.adoptRoom({ id: ctx.params.id });
+      if (isNav) { room = karvanModel.adoptRoom({ id: ctx.params.id }); justAdopted = !!room; }
     }
     if (!room) { ctx.redirect('/karvan'); return; }
+    if (justAdopted) { // al unirte por enlace, registra el feed de quien te invitó → relay cross-device
+      const author = await karvanInviteAuthor(ctx.params.id);
+      if (author) { karvanModel.addRemoteFeed(ctx.params.id, author); karvanStartRelay(); }
+    }
     let selfId = ''; try { selfId = getViewerId(); } catch (e) {}
     const msgs = karvanModel.listMessages(room.id, 0) || [];
     ctx.body = karvanRoomView(room, msgs, { selfId, invite: ctx.query.invite || '' });
@@ -3679,6 +3737,7 @@ router
       // le llega al INBOX del contacto con un enlace a la sala. Sin código SSB nuevo.
       await pmModel.sendMessage([to], 'KARVAN_INVITE',
         'You have been invited to an ephemeral Karvan room' + (room.title ? ' ("' + room.title + '")' : '') + ' -> /karvan/' + id);
+      karvanModel.addRemoteFeed(id, to); karvanStartRelay(); // relay cross-device hacia el invitado
       ctx.redirect('/karvan/' + id + '?invite=ok');
     } catch (e) { ctx.redirect('/karvan/' + id + '?invite=fail'); }
   })
@@ -3692,6 +3751,7 @@ router
       mid: b.mid,
     });
     if (!msg) { ctx.status = 404; ctx.body = { error: 'no room' }; return; }
+    karvanPublishRelay(ctx.params.id, msg.mid || (msg.from + '-' + msg.ts + '-' + msg.seq), msg.from, msg.text); // → feeds remotos (si hay)
     const wantsJson = (ctx.get('accept') || '').indexOf('application/json') !== -1
       || (ctx.get('content-type') || '').indexOf('application/json') !== -1;
     if (wantsJson) ctx.body = { ok: true, seq: msg.seq };