db_sync: add diagnostic logs for message sync debugging during join

- db_handle_init_sync: TRACE→INFO with peer_cnt/my_cnt/tp_offset
- db_handle_send_data: detailed batch info (range, remaining count)
- db_sync_initiate_sync: add table name to log
- db_sync_on_conn_up: add first table name to summary log

src/db_sync.c

@@ -604,7 +604,7 @@ static void db_handle_init_sync(struct DB_SYNC_INSTANCE* si, uint64_t src, const
     if (len < 4) { DEBUG_ERROR(DEBUG_CATEGORY_DB_SYNC, "INIT_SYNC too short %zu from %016llx", len, (unsigned long long)src); return; }
     uint32_t pc = *(uint32_t*)p;
     uint32_t mc = db_count(si);
-    DEBUG_TRACE(DEBUG_CATEGORY_DB_SYNC, "from=%016llx peer_cnt=%u my=%u tbl=%s", (unsigned long long)src, pc, mc, SI_TBL(si));
+    DEBUG_INFO(DEBUG_CATEGORY_DB_SYNC, "INIT_SYNC from=%016llx peer_cnt=%u my_cnt=%u tbl=%s → tp_offset=%u", (unsigned long long)src, pc, mc, SI_TBL(si), (pc < mc ? pc : mc));
     uint32_t tp = (pc < mc ? pc : mc);
     if (tp > 0) tp--;
 
@@ -943,12 +943,15 @@ static void db_handle_send_data(struct DB_SYNC_INSTANCE* si, uint64_t src, const
 
     if (mc > pk && sp && sp->sync_state == 1) {
         uint32_t scnt = mc - pk; if (scnt > DB_SEND_DATA_MAX) scnt = DB_SEND_DATA_MAX;
-        DEBUG_INFO(DEBUG_CATEGORY_DB_SYNC, "send_data continue to %016llx from=%u cnt=%u mc=%u",
-                   (unsigned long long)src, pk, scnt, mc);
+        DEBUG_INFO(DEBUG_CATEGORY_DB_SYNC, "db_sync SEND_DATA batch: %u records [%u..%u/%u] → still %u remaining",
+                   received, from, from + received - 1, mc, mc - pk);
         si_send_data_batch(si, src, pk, scnt, 1);
     } else if (mc > pk) {
-        DEBUG_INFO(DEBUG_CATEGORY_DB_SYNC, "send_data stopping to %016llx — mc=%u pk=%u state=%d",
-                   (unsigned long long)src, mc, pk, sp ? sp->sync_state : -1);
+        DEBUG_INFO(DEBUG_CATEGORY_DB_SYNC, "db_sync SEND_DATA batch: %u records [%u..%u/%u] — stopping (state=%d)",
+                   received, from, from + received - 1, mc, sp ? sp->sync_state : -1);
+    } else {
+        DEBUG_INFO(DEBUG_CATEGORY_DB_SYNC, "db_sync SEND_DATA batch: %u records [%u..%u/%u] — all caught up (state=%d)",
+                   received, from, from + received - 1, mc, sp ? sp->sync_state : -1);
     }
 
     uint32_t nc = db_count(si);
@@ -1162,9 +1165,10 @@ static void db_sync_on_conn_up(struct ETCP_CONN* conn, void* arg)
         synced++;
     }
     DEBUG_INFO(DEBUG_CATEGORY_DB_SYNC,
-               "conn_up peer=%016llx init=%d links=%d instances=%d synced=%d skipped_state=%d skipped_not_ready=%d",
+               "conn_up peer=%016llx init=%d links=%d instances=%d synced=%d skipped_state=%d skipped_not_ready=%d tbls=[%s]",
                (unsigned long long)pid, conn->initialized, conn->links_up,
-               db->instance_count, synced, skipped_state, skipped_not_ready);
+               db->instance_count, synced, skipped_state, skipped_not_ready,
+               (synced > 0 && db->instance_count > 0) ? db->instances[0].table_name : "none");
 }
 
 static void db_sync_on_conn_down(struct ETCP_CONN* conn, void* arg)
@@ -1208,7 +1212,7 @@ static void db_sync_initiate_sync(struct DB_SYNC_INSTANCE* si, uint64_t pid)
     msg[0] = DB_MSG_INIT_SYNC;
     memcpy(msg + 1, &mc, 4);
     db_sync_send(si, pid, msg, 5);
-    DEBUG_INFO(DEBUG_CATEGORY_DB_SYNC, "INIT_SYNC -> %016llx my=%u", (unsigned long long)pid, mc);
+    DEBUG_INFO(DEBUG_CATEGORY_DB_SYNC, "INIT_SYNC → %016llx my=%u tbl=%s", (unsigned long long)pid, mc, SI_TBL(si));
 }
 
 static void db_verify_chain(struct DB_SYNC_INSTANCE* si)