db_sync: lazy-register channel instance on INIT_SYNC when not pre-registered

When INIT_SYNC arrives for an unknown hash, scan all msg_* tables in
sqlite_master, compute SHA256 of channel_id, match the hash, and
auto-register via db_sync_instance_add. Fixes invite flow where
channel was created but db_sync wasn't notified.

src/db_sync.c

@@ -1059,13 +1059,34 @@ static void db_sync_recv_cb(struct ETCP_CONN* conn, struct ll_entry* entry)
 
     struct DB_SYNC_INSTANCE* si = db_instance_find(db, hash);
     if (!si) {
-        DEBUG_INFO(DEBUG_CATEGORY_DB_SYNC,
-                   "recv msg type=0x%02x from %016llx hash=%016llx — instance NOT FOUND; sending DB_ERR_NOT_FOUND",
-                   type, (unsigned long long)src, (unsigned long long)hash);
-        DEBUG_TRACE(DEBUG_CATEGORY_DB_SYNC, "→ instance not found for hash=%016llx", (unsigned long long)hash);
-        uint8_t err[2]; err[0] = DB_MSG_ERROR; err[1] = DB_ERR_NOT_FOUND;
-        db_sync_send_hash(db, src, hash, err, 2);
-        queue_dgram_free(entry); queue_entry_free(entry); return;
+        /* lazy-register: find table msg_<ch_id> with matching SHA256 */
+        sqlite3_stmt* st = NULL;
+        if (sqlite3_prepare_v2(db->db,
+                "SELECT name, substr(name,5) FROM sqlite_master WHERE type='table' AND name LIKE 'msg_%'",
+                -1, &st, NULL) == SQLITE_OK) {
+            while (sqlite3_step(st) == SQLITE_ROW) {
+                const char* tbl = (const char*)sqlite3_column_text(st, 0);
+                const char* ch_id = (const char*)sqlite3_column_text(st, 1);
+                if (!ch_id || !ch_id[0]) continue;
+                uint64_t h; { uint8_t sh[32]; SC_SHA256_CTX ctx; sc_sha256_init(&ctx); sc_sha256_update(&ctx, (const uint8_t*)ch_id, strlen(ch_id)); sc_sha256_final(&ctx, sh); memcpy(&h, sh, 8); }
+                if (h == hash) {
+                    si = db_sync_instance_add(db->inst, tbl, hash);
+                    if (si) { si_peer_add(si, src); }
+                    DEBUG_INFO(DEBUG_CATEGORY_DB_SYNC, "lazy-register: tbl=%s ch=%s hash=%016llx", tbl, ch_id, (unsigned long long)hash);
+                    break;
+                }
+            }
+            sqlite3_finalize(st);
+        }
+        if (!si) {
+            DEBUG_INFO(DEBUG_CATEGORY_DB_SYNC,
+                       "recv msg type=0x%02x from %016llx hash=%016llx — instance NOT FOUND; sending DB_ERR_NOT_FOUND",
+                       type, (unsigned long long)src, (unsigned long long)hash);
+            DEBUG_TRACE(DEBUG_CATEGORY_DB_SYNC, "→ instance not found for hash=%016llx", (unsigned long long)hash);
+            uint8_t err[2]; err[0] = DB_MSG_ERROR; err[1] = DB_ERR_NOT_FOUND;
+            db_sync_send_hash(db, src, hash, err, 2);
+            queue_dgram_free(entry); queue_entry_free(entry); return;
+        }
     }
     if (!si->enabled) {
         uint8_t err[2]; err[0] = DB_MSG_ERROR; err[1] = DB_ERR_DISABLED;