diff --git a/src/chat/db_sync.c b/src/chat/db_sync.c
index a94e3980..8a533995 100644
--- a/src/chat/db_sync.c
+++ b/src/chat/db_sync.c
@@ -531,6 +531,9 @@ static int db_verify_author_sig(struct DB_SYNC_INSTANCE* si,
                                 const char* json, size_t jlen,
                                 const uint8_t* sig)
 {
+    if (!sig || jlen > DB_SYNC_MESSAGE_MAX || (jlen && !json)) {
+        DEBUG_ERROR(DEBUG_CATEGORY_CHAT_SYNC, "history: invalid signed body tbl=%s bytes=%zu", SI_TBL(si), jlen); return -1;
+    }
     uint8_t pubkey[32];
     if (db_get_ed25519_pubkey(si->db_sync, author_node_id, pubkey) != 0) {
         DEBUG_WARN(DEBUG_CATEGORY_CHAT_SYNC,
@@ -638,7 +641,11 @@ static int db_record_insert_cascade(struct DB_SYNC_INSTANCE* si,
     int ret = db_record_insert(si, rid, rts, rauthor, rdata, rdlen, rsig, local_attrs);
     if (ret != 0) return ret;
 
-    if (si->on_insert) si->on_insert(si, rts, rdata, rdlen, rauthor, initial_sync, si->on_insert_arg);
+    if (si->on_insert) {
+        uint8_t message_id[32];
+        if (chat_message_id(si->group_id, rts, rsig, message_id) < 0) return -1;
+        si->on_insert(si, message_id, rts, rdata, rdlen, rauthor, initial_sync, si->on_insert_arg);
+    }
 
     uint8_t pbuf[4096]; uint32_t poff = 1; pbuf[0] = DB_MSG_PUSH;
     memcpy(pbuf + poff, &rid, 8);     poff += 8;
diff --git a/src/chat/db_sync.h b/src/chat/db_sync.h
index 544af5d2..b8bb0dee 100644
--- a/src/chat/db_sync.h
+++ b/src/chat/db_sync.h
@@ -30,6 +30,9 @@ struct DB_SYNC_INSTANCE;
 #define DB_MSG_ERROR        0x08
 #define DB_MSG_REQUEST_SYNC 0x09
 
+/* PUSH имеет фиксированный буфер 4096 байт; 4000 оставляет место заголовку и подписи. */
+#define DB_SYNC_MESSAGE_MAX 4000
+
 // SEND_DATA want_from sentinel
 #define DB_WANT_FROM_NONE   0xFFFFFFFF  // no request for peer's data
 
@@ -102,6 +105,7 @@ int      db_sync_select(struct DB_SYNC_INSTANCE* si, uint32_t offset, uint32_t l
 // initial_sync = 1 если запись пришла в рамках bulk-обмена SEND_DATA (initial/re-sync),
 //                0 для live-PUSH и локальных вставок.
 typedef void (*db_sync_insert_cb)(struct DB_SYNC_INSTANCE* si,
+                                   const uint8_t message_id[32],
                                    uint64_t record_timestamp,
                                    const char* json_data, size_t len,
                                    uint64_t author_node_id, int initial_sync, void* arg);