diff --git a/tests/Makefile.am b/tests/Makefile.am
index 65c524f1..f5ecea7c 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -82,6 +82,7 @@ check_PROGRAMS = \
 	test_node_snapshot \
 	test_ncd_config \
 	test_db_sync \
+	test_db_sync_schema \
 	test_merkle_sync \
 	test_merkle_protocol \
 	test_chat_feedback \
@@ -488,6 +489,10 @@ test_db_sync_SOURCES = test_db_sync.c
 test_db_sync_CFLAGS = -I$(top_srcdir)/src -I$(top_srcdir)/lib
 test_db_sync_LDADD = $(LIBUTUN) $(CRYPTO_LIBS) $(COMMON_LIBS)
 
+test_db_sync_schema_SOURCES = test_db_sync_schema.c
+test_db_sync_schema_CFLAGS = -I$(top_srcdir)/src -I$(top_srcdir)/lib
+test_db_sync_schema_LDADD = $(LIBUTUN) $(CRYPTO_LIBS) $(COMMON_LIBS)
+
 test_merkle_sync_SOURCES = test_merkle_sync.c
 test_chat_feedback_SOURCES = test_chat_feedback.c
 test_chat_feedback_CFLAGS = -I$(top_srcdir)/src -I$(top_srcdir)/src/chat -I$(top_srcdir)/lib
diff --git a/tests/test_db_sync_schema.c b/tests/test_db_sync_schema.c
new file mode 100644
index 00000000..4c7e559d
--- /dev/null
+++ b/tests/test_db_sync_schema.c
@@ -0,0 +1,144 @@
+/* Сохранение настоящей истории при обновлении схемы, повторный запуск и атомарный отказ. */
+#include "../src/utun_instance.h"
+#include "../src/config_parser.h"
+#include "../src/chat/chat_core.h"
+#include "../src/chat/chat_feedback.h"
+#include "../src/chat/db_sync.h"
+#include "../src/routing_layer/topo_group.h"
+#include "../src/transport_layer/secure_channel.h"
+#include "../lib/debug_config.h"
+#include <assert.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#define OLD_COLUMNS "timestamp,node_id,id,chain_hash,flags,data,author_signature,local_attrs,delivered_peers,delivery_chain"
+
+static void execute(sqlite3* db, const char* sql) {
+    int rc = sqlite3_exec(db, sql, NULL, NULL, NULL);
+    if (rc != SQLITE_OK) DEBUG_ERROR(DEBUG_CATEGORY_CHAT_SYNC, "schema test SQL=%s: %s", sql, sqlite3_errmsg(db));
+    assert(rc == SQLITE_OK);
+}
+
+static sqlite3_int64 number(sqlite3* db, const char* sql) {
+    sqlite3_stmt* st = NULL;
+    assert(sqlite3_prepare_v2(db, sql, -1, &st, NULL) == SQLITE_OK && sqlite3_step(st) == SQLITE_ROW);
+    sqlite3_int64 value = sqlite3_column_int64(st, 0); sqlite3_finalize(st); return value;
+}
+
+static void legacy_table(sqlite3* db, const char* name) {
+    char sql[1024];
+    snprintf(sql, sizeof(sql), "CREATE TABLE \"%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,local_attrs TEXT DEFAULT '',delivered_peers INTEGER NOT NULL DEFAULT 0,"
+        "delivery_chain TEXT NOT NULL DEFAULT '',PRIMARY KEY(timestamp,author_signature));"
+        "CREATE INDEX \"idx_%s_ttl\" ON \"%s\" (node_id,timestamp)", name, name, name);
+    execute(db, sql);
+}
+
+static void check_history(sqlite3* db, const char* table, uint64_t group) {
+    char sql[768];
+    snprintf(sql, sizeof(sql), "SELECT count(*) FROM (SELECT " OLD_COLUMNS " FROM \"%s\" EXCEPT SELECT * FROM expected)", table);
+    assert(number(db, sql) == 0);
+    snprintf(sql, sizeof(sql), "SELECT count(*) FROM (SELECT * FROM expected EXCEPT SELECT " OLD_COLUMNS " FROM \"%s\")", table);
+    assert(number(db, sql) == 0);
+    snprintf(sql, sizeof(sql), "SELECT timestamp,author_signature,message_id FROM \"%s\"", table);
+    sqlite3_stmt* st = NULL; assert(sqlite3_prepare_v2(db, sql, -1, &st, NULL) == SQLITE_OK);
+    int rc;
+    while ((rc = sqlite3_step(st)) == SQLITE_ROW) {
+        uint8_t id[32]; assert(sqlite3_column_bytes(st, 1) == 64 && sqlite3_column_bytes(st, 2) == 32);
+        assert(chat_message_id(group, (uint64_t)sqlite3_column_int64(st, 0), sqlite3_column_blob(st, 1), id) == 0);
+        assert(!memcmp(id, sqlite3_column_blob(st, 2), 32));
+    }
+    assert(rc == SQLITE_DONE); sqlite3_finalize(st);
+    snprintf(sql, sizeof(sql), "SELECT count(*) FROM sqlite_master WHERE type='index' AND name='idx_%s_ttl'", table);
+    assert(number(db, sql) == 1 && number(db, "SELECT count(*) FROM sqlite_master WHERE name LIKE 'new_msg_%'") == 0);
+    assert(sqlite3_get_autocommit(db));
+}
+
+static struct chat_msg_submit send_text(struct UTUN_INSTANCE* inst, const char* channel, const char* text) {
+    struct chat_msg_submit req = { .inst = inst, .data = (const uint8_t*)text, .data_len = strlen(text) };
+    snprintf(req.channel_id, sizeof(req.channel_id), "%s", channel); strcpy(req.content_type, "text");
+    assert(chat_core_submit_message(inst, &req) == 0); return req;
+}
+
+/* Дополнительный режим проверяет копии пользовательских БД через тот же публичный API. */
+static void check_copy(struct UTUN_INSTANCE* inst) {
+    sqlite3* db = inst->topo_sqlite_db; char** tables = NULL; int rows, columns;
+    assert(sqlite3_get_table(db, "SELECT name FROM sqlite_master WHERE type='table' AND name GLOB 'msg_[0-9]*'",
+        &tables, &rows, &columns, NULL) == SQLITE_OK);
+    assert(db_sync_enable(inst) == 0);
+    for (int i = 0; i < rows; i++) {
+        const char* table = tables[i + 1]; uint64_t gid = strtoull(table + 4, NULL, 10); assert(gid);
+        assert(topo_groups_create_group(inst->topo_groups, gid, TOPO_GROUP_TYPE_CHAT, table + 4));
+        char sql[768]; snprintf(sql, sizeof(sql), "CREATE TEMP TABLE expected AS SELECT " OLD_COLUMNS " FROM \"%s\"", table);
+        execute(db, sql); struct DB_SYNC_INSTANCE* si = db_sync_instance_add(inst, table, gid); assert(si);
+        check_history(db, table, gid); db_sync_instance_remove(si);
+        si = db_sync_instance_add(inst, table, gid); assert(si); check_history(db, table, gid); db_sync_instance_remove(si);
+        execute(db, "DROP TABLE expected");
+    }
+    sqlite3_free_table(tables); DEBUG_INFO(DEBUG_CATEGORY_CHAT_SYNC, "PASS: user DB copy, tables=%d, all fields preserved", rows);
+}
+
+int main(int argc, char** argv) {
+    debug_config_init(); debug_set_level(DEBUG_LEVEL_WARN); debug_set_category_level(DEBUG_CATEGORY_CHAT_SYNC, DEBUG_LEVEL_INFO);
+    struct UASYNC* ua = uasync_create(); assert(ua); char config[2048];
+    snprintf(config, sizeof(config),
+        "[global]\nmy_private_key=704f2e012c8fa8768130cb0f988a997dccb628372bc5ceccacc78dcbfec5916f\n"
+        "my_public_key=b3193173def895bd0fcea6f86af077c7d77216f10395275f627ac18242ec0f01\n"
+        "db_path=%s\n[routing]\nmy_subnet=192.168.42.0/24\n[server: udp]\naddr=127.0.0.1:0\ntype=public\n"
+        "[chatserver]\ngroup_autoconnect=0\nstorage_autoload=0\n", argc == 2 ? argv[1] : "");
+    struct UTUN_INSTANCE* inst = utun_instance_create_from_str(ua, config); assert(inst && utun_core_start(inst) == 0);
+    if (argc == 2) { check_copy(inst); goto done; }
+    assert(chat_service_start(inst) == 0); chat_core_create_channel_auto(inst, "Stored history");
+    sqlite3* db = inst->topo_sqlite_db; sqlite3_stmt* st = NULL;
+    assert(sqlite3_prepare_v2(db, "SELECT channel_id FROM channels", -1, &st, NULL) == SQLITE_OK && sqlite3_step(st) == SQLITE_ROW);
+    char channel[21], table[32], sql[1024]; snprintf(channel, sizeof(channel), "%s", sqlite3_column_text(st, 0)); sqlite3_finalize(st);
+    snprintf(table, sizeof(table), "msg_%s", channel); uint64_t gid = strtoull(channel, NULL, 10);
+    struct chat_msg_submit first = send_text(inst, channel, "История \"с кавычками\"\n👍");
+    send_text(inst, channel, "Второе сообщение");
+    /* Один timestamp и разные подписи должны получить разные стабильные ID. */
+    const char* json = "{\"ct\":\"text\",\"d\":\"same timestamp\"}"; uint8_t body[128], signature[64];
+    memcpy(body, &first.timestamp, 8); memcpy(body + 8, json, strlen(json));
+    assert(sc_ed25519_sign(inst->my_ed25519_privkey, body, 8 + strlen(json), signature) == SC_OK);
+    assert(db_sync_insert_signed(db_sync_instance_find(inst, gid), json, strlen(json), signature, 64, first.timestamp, NULL) == 0);
+    uasync_poll(ua, 0);
+    snprintf(sql, sizeof(sql), "UPDATE \"%s\" SET flags=1,local_attrs=NULL,delivered_peers=7,delivery_chain='saved chain';"
+        "CREATE TEMP TABLE expected AS SELECT " OLD_COLUMNS " FROM \"%s\"", table, table); execute(db, sql);
+    chat_core_create_channel_auto(inst, "Empty history"); chat_service_stop(inst);
+    /* Воспроизводим старую схему всех каналов, чтобы тест покрывал DDL при загрузке списка каналов. */
+    char** tables = NULL; int rows, columns;
+    assert(sqlite3_get_table(db, "SELECT name FROM sqlite_master WHERE type='table' AND name LIKE 'msg_%'",
+        &tables, &rows, &columns, NULL) == SQLITE_OK);
+    for (int i = 0; i < rows; i++) {
+        const char* name = tables[i + 1]; snprintf(sql, sizeof(sql), "ALTER TABLE \"%s\" RENAME TO saved", name); execute(db, sql);
+        legacy_table(db, name); snprintf(sql, sizeof(sql), "INSERT INTO \"%s\" SELECT " OLD_COLUMNS " FROM saved;DROP TABLE saved", name);
+        execute(db, sql);
+    }
+    sqlite3_free_table(tables);
+    assert(chat_service_start(inst) == 0); check_history(db, table, gid); assert(chat_core_count(inst, channel) == 3);
+    char listing[8192]; size_t len;
+    assert(chat_core_get_messages_json(inst, channel, 10, 0, listing, sizeof(listing), &len) == 0 && len > 0);
+    snprintf(sql, sizeof(sql), "INSERT INTO \"%s\" (" OLD_COLUMNS ") SELECT * FROM expected", table);
+    assert(sqlite3_exec(db, sql, NULL, NULL, NULL) == SQLITE_CONSTRAINT);
+    snprintf(sql, sizeof(sql), "INSERT INTO \"%s\" (" OLD_COLUMNS ",message_id) SELECT *,x'01' FROM expected", table);
+    assert(sqlite3_exec(db, sql, NULL, NULL, NULL) == SQLITE_CONSTRAINT);
+    chat_service_stop(inst); assert(chat_service_start(inst) == 0); check_history(db, table, gid);
+    send_text(inst, channel, "Отправка после обновления 👍"); assert(chat_core_count(inst, channel) == 4);
+    DEBUG_INFO(DEBUG_CATEGORY_CHAT_SYNC, "PASS: restart, empty table, preserved fields, canonical IDs and new message submission");
+    /* Ошибка после копирования первой строки должна откатить всю перестройку. */
+    assert(topo_groups_create_group(inst->topo_groups, 9001, TOPO_GROUP_TYPE_CHAT, "9001")); legacy_table(db, "msg_9001");
+    execute(db, "INSERT INTO msg_9001 VALUES(1,1,1,zeroblob(32),0,x'01',zeroblob(64),'kept',0,'');"
+        "INSERT INTO msg_9001 VALUES(2,1,2,zeroblob(32),0,x'02',zeroblob(3),'kept',0,'')");
+    assert(!db_sync_instance_add(inst, "msg_9001", 9001));
+    assert(sqlite3_get_autocommit(db) && number(db, "SELECT count(*) FROM msg_9001") == 2);
+    assert(number(db, "SELECT count(*) FROM pragma_table_info('msg_9001') WHERE name='message_id'") == 0);
+    assert(number(db, "SELECT count(*) FROM sqlite_master WHERE name='new_msg_9001'") == 0);
+    execute(db, "UPDATE msg_9001 SET author_signature=zeroblob(64) WHERE timestamp=2");
+    struct DB_SYNC_INSTANCE* si = db_sync_instance_add(inst, "msg_9001", 9001); assert(si && db_sync_count(si) == 2);
+    DEBUG_INFO(DEBUG_CATEGORY_CHAT_SYNC, "PASS: partial-copy failure rolls back, registration can be retried");
+done:
+    utun_instance_destroy(inst); uasync_poll(ua, 0);
+    assert(ua->timer_alloc_count == ua->timer_free_count && ua->socket_alloc_count == ua->socket_free_count);
+    uasync_destroy(ua, 0); puts("ALL PASS: chat history schema repair"); return 0;
+}