diff --git a/src/chat/chat_core.c b/src/chat/chat_core.c
index d62c3783..455b31e6 100644
--- a/src/chat/chat_core.c
+++ b/src/chat/chat_core.c
@@ -212,19 +212,22 @@ int chat_core_init(struct UTUN_INSTANCE* inst, const char* db_path) {
         }
     }
 
-    /* ensure infrastructure for all existing channels (survives restart) */
+    /* Сначала закрываем чтение каналов: активный statement блокирует перестройку таблиц истории. */
     {
-        sqlite3_stmt* stmt = NULL;
-        if (sqlite3_prepare_v2(cc->db, "SELECT channel_id FROM channels ORDER BY created_at ASC",
-                                -1, &stmt, NULL) == SQLITE_OK) {
-            int loaded = 0;
-            while (sqlite3_step(stmt) == SQLITE_ROW) {
-                const char* ch = (const char*)sqlite3_column_text(stmt, 0);
-                if (ch && ch[0]) { chat_core_ensure_channel_ready(inst, ch); loaded++; }
-            }
-            sqlite3_finalize(stmt);
-            DEBUG_INFO(DEBUG_CATEGORY_CHAT_SYNC, "%s: loaded %d channels from DB", CC_ID, loaded);
+        char** channels = NULL;
+        int rows = 0, columns = 0, loaded = 0;
+        int rc = sqlite3_get_table(cc->db, "SELECT channel_id FROM channels ORDER BY created_at ASC",
+            &channels, &rows, &columns, NULL);
+        if (rc != SQLITE_OK) {
+            DEBUG_ERROR(DEBUG_CATEGORY_CHAT_SYNC, "%s: load channels: %s", CC_ID, sqlite3_errmsg(cc->db));
+            sqlite3_free_table(channels); chat_core_destroy(inst); return -1;
+        }
+        for (int i = 0; i < rows; i++) {
+            const char* ch = channels[(i + 1) * columns];
+            if (ch && ch[0]) { chat_core_ensure_channel_ready(inst, ch); loaded++; }
         }
+        sqlite3_free_table(channels);
+        DEBUG_INFO(DEBUG_CATEGORY_CHAT_SYNC, "%s: loaded %d channels from DB", CC_ID, loaded);
     }
 
     DEBUG_INFO(DEBUG_CATEGORY_CHAT_SYNC, "%s: initialized, db=%s node_id=0x%016llx",
diff --git a/src/chat/db_sync.c b/src/chat/db_sync.c
index 8a533995..0decca59 100644
--- a/src/chat/db_sync.c
+++ b/src/chat/db_sync.c
@@ -149,6 +149,99 @@ static int si_prep(struct DB_SYNC_INSTANCE* si, sqlite3_stmt** stmt, const char*
     return sqlite3_prepare_v2(SI_DB(si), sql, -1, stmt, NULL);
 }
 
+// Одна схема для новых таблиц и однократного преобразования сохранённой истории.
+static int si_table_create(struct DB_SYNC_INSTANCE* si, const char* name, int if_not_exists) {
+    char sql[768];
+    snprintf(sql, sizeof(sql),
+        "CREATE TABLE %s\"%s\" ("
+        " timestamp INTEGER NOT NULL, node_id INTEGER NOT NULL, id INTEGER NOT NULL,"
+        " chain_hash BLOB NOT NULL, flags INTEGER NOT NULL DEFAULT 0, data BLOB,"
+        " author_signature BLOB NOT NULL, message_id BLOB NOT NULL UNIQUE CHECK(length(message_id)=32),"
+        " local_attrs TEXT DEFAULT '', delivered_peers INTEGER NOT NULL DEFAULT 0,"
+        " delivery_chain TEXT NOT NULL DEFAULT '', PRIMARY KEY(timestamp,author_signature))",
+        if_not_exists ? "IF NOT EXISTS " : "", name);
+    if (sqlite3_exec(SI_DB(si), sql, NULL, NULL, NULL) == SQLITE_OK) return 0;
+    DEBUG_ERROR(DEBUG_CATEGORY_CHAT_SYNC, "history schema: create table=%s: %s", name, sqlite3_errmsg(SI_DB(si))); return -1;
+}
+
+// Перестройка атомарна: сохраняем подписи, цепочку, локальные атрибуты и доставку без изменений.
+static int si_table_init(struct DB_SYNC_INSTANCE* si) {
+    sqlite3* db = SI_DB(si);
+    if (si_table_create(si, SI_TBL(si), 1) < 0) return -1;
+    sqlite3_stmt *rows = NULL, *insert = NULL;
+    const char* stage = "inspect columns";
+    int rc = si_prep(si, &rows, "PRAGMA table_info(\"%s\")"), has_id = 0;
+    if (rc != SQLITE_OK) goto error;
+    while ((rc = sqlite3_step(rows)) == SQLITE_ROW) {
+        const char* name = (const char*)sqlite3_column_text(rows, 1);
+        if (name && !strcmp(name, "message_id")) has_id = 1;
+    }
+    if (rc != SQLITE_DONE) goto error;
+    sqlite3_finalize(rows); rows = NULL;
+    if (has_id) return 0;
+
+    stage = "begin";
+    if (sqlite3_exec(db, "BEGIN IMMEDIATE", NULL, NULL, NULL) != SQLITE_OK) goto error;
+    DEBUG_INFO(DEBUG_CATEGORY_CHAT_SYNC, "history schema: adding message_id table=%s group=%016llx",
+        SI_TBL(si), (unsigned long long)si->group_id);
+    char replacement[64], sql[768];
+    snprintf(replacement, sizeof(replacement), "new_%s", SI_TBL(si));
+    stage = "create replacement";
+    if (si_table_create(si, replacement, 0) < 0) goto rollback;
+    stage = "read history";
+    if (si_prep(si, &rows, "SELECT timestamp,author_signature FROM \"%s\"") != SQLITE_OK) goto rollback;
+    snprintf(sql, sizeof(sql),
+        "INSERT INTO \"%s\" SELECT timestamp,node_id,id,chain_hash,flags,data,author_signature,?1,"
+        "local_attrs,delivered_peers,delivery_chain FROM \"%s\" WHERE timestamp=?2 AND author_signature=?3",
+        replacement, SI_TBL(si));
+    stage = "prepare copy";
+    if (sqlite3_prepare_v2(db, sql, -1, &insert, NULL) != SQLITE_OK) goto rollback;
+    sqlite3_int64 count = 0;
+    while ((rc = sqlite3_step(rows)) == SQLITE_ROW) {
+        sqlite3_int64 ts = sqlite3_column_int64(rows, 0);
+        const uint8_t* signature = sqlite3_column_blob(rows, 1);
+        int size = sqlite3_column_bytes(rows, 1);
+        uint8_t message_id[32];
+        stage = "compute message_id";
+        if (!signature || size != DB_SIG_SIZE || chat_message_id(si->group_id, (uint64_t)ts, signature, message_id) < 0) {
+            DEBUG_ERROR(DEBUG_CATEGORY_CHAT_SYNC, "history schema: invalid identity table=%s ts=%lld signature_bytes=%d",
+                SI_TBL(si), (long long)ts, size); goto rollback;
+        }
+        stage = "copy record";
+        rc = sqlite3_bind_blob(insert, 1, message_id, sizeof(message_id), SQLITE_STATIC);
+        if (rc == SQLITE_OK) rc = sqlite3_bind_int64(insert, 2, ts);
+        if (rc == SQLITE_OK) rc = sqlite3_bind_blob(insert, 3, signature, DB_SIG_SIZE, SQLITE_STATIC);
+        if (rc != SQLITE_OK || sqlite3_step(insert) != SQLITE_DONE) goto rollback;
+        if (sqlite3_changes(db) != 1) {
+            DEBUG_ERROR(DEBUG_CATEGORY_CHAT_SYNC, "history schema: copy table=%s ts=%lld changed=%d expected=1",
+                SI_TBL(si), (long long)ts, sqlite3_changes(db)); goto rollback;
+        }
+        if (sqlite3_reset(insert) != SQLITE_OK) goto rollback;
+        count++;
+    }
+    stage = "read history";
+    if (rc != SQLITE_DONE) goto rollback;
+    sqlite3_finalize(rows); rows = NULL; sqlite3_finalize(insert); insert = NULL;
+    stage = "replace table";
+    snprintf(sql, sizeof(sql), "DROP TABLE \"%s\"; ALTER TABLE \"%s\" RENAME TO \"%s\"",
+        SI_TBL(si), replacement, SI_TBL(si));
+    if (sqlite3_exec(db, sql, NULL, NULL, NULL) != SQLITE_OK) goto rollback;
+    stage = "commit";
+    if (sqlite3_exec(db, "COMMIT", NULL, NULL, NULL) != SQLITE_OK) goto rollback;
+    DEBUG_INFO(DEBUG_CATEGORY_CHAT_SYNC, "history schema: message_id ready table=%s records=%lld", SI_TBL(si), (long long)count);
+    return 0;
+rollback:
+    DEBUG_ERROR(DEBUG_CATEGORY_CHAT_SYNC, "history schema: table=%s stage=%s: %s; rolling back",
+        SI_TBL(si), stage, sqlite3_errmsg(db));
+    sqlite3_finalize(rows); sqlite3_finalize(insert);
+    if (sqlite3_exec(db, "ROLLBACK", NULL, NULL, NULL) != SQLITE_OK)
+        DEBUG_ERROR(DEBUG_CATEGORY_CHAT_SYNC, "history schema: rollback table=%s: %s", SI_TBL(si), sqlite3_errmsg(db));
+    return -1;
+error:
+    DEBUG_ERROR(DEBUG_CATEGORY_CHAT_SYNC, "history schema: table=%s stage=%s: %s", SI_TBL(si), stage, sqlite3_errmsg(db));
+    sqlite3_finalize(rows); return -1;
+}
+
 // ============================================================
 // SQLite open/close
 // ============================================================
@@ -1717,34 +1810,16 @@ struct DB_SYNC_INSTANCE* db_sync_instance_add(struct UTUN_INSTANCE* inst, const
     si->group_id = group_id;
     snprintf(si->table_name, sizeof(si->table_name), "%s", table_name);
 
-    // Create table — PK is (timestamp, node_id), author_signature NOT NULL
+    if (si_table_init(si) < 0) { db_sync_instance_remove(si); return NULL; }
+
+    // Производный TTL-индекс создаём также после перестройки таблицы.
     {
         char sql[768];
-        snprintf(sql, sizeof(sql),
-                 "CREATE TABLE IF NOT EXISTS \"%s\" ("
-                 " timestamp INTEGER NOT NULL,"
-                 " node_id INTEGER NOT NULL,"
-                 " id INTEGER NOT NULL,"
-                 " chain_hash BLOB NOT NULL,"
-                 " flags INTEGER NOT NULL DEFAULT 0,"
-                 " data BLOB,"
-                 " author_signature BLOB NOT NULL,"
-                 " message_id BLOB NOT NULL UNIQUE CHECK(length(message_id)=32),"
-                 " local_attrs TEXT DEFAULT '',"
-                 " delivered_peers INTEGER NOT NULL DEFAULT 0,"
-                 " delivery_chain TEXT NOT NULL DEFAULT '',"
-                 " PRIMARY KEY (timestamp, author_signature))",
-                 si->table_name);
-        int rc = sqlite3_exec(db->db, sql, NULL, NULL, NULL);
-        if (rc != SQLITE_OK) {
-            DEBUG_ERROR(DEBUG_CATEGORY_CHAT_SYNC, "CREATE TABLE %s: %s", si->table_name, sqlite3_errmsg(db->db));
-            db_sync_instance_remove(si); return NULL;
-        }
         snprintf(sql, sizeof(sql),
                  "CREATE INDEX IF NOT EXISTS \"idx_%s_ttl\""
                  " ON \"%s\" (node_id, timestamp)",
                  si->table_name, si->table_name);
-        rc = sqlite3_exec(db->db, sql, NULL, NULL, NULL);
+        int rc = sqlite3_exec(db->db, sql, NULL, NULL, NULL);
         if (rc != SQLITE_OK) DEBUG_ERROR(DEBUG_CATEGORY_CHAT_SYNC, "CREATE INDEX %s: %s", si->table_name, sqlite3_errmsg(db->db));
     }