feat(iot_mqtt): 恢复 loop_data 完整字段 + 分批发送(2通道/包)

按 DLD960_TCP_JSON协议.md §5.1 恢复完整字段:
- ch, freq_level, has_car, loop_ok, freq_current, freq_diff,
  sensitivity, condition, misc.type, misc.value

每包发 2 个通道，确保 JSON < 450 字节 (mqttBuf 512 安全范围内)。
4 通道设备每次 SensorReport 发 2 条 loop_data 消息。

vd960DBN/BLE/OnlyUpdateApp_Peripheral/APP/iot_mqtt_srv.c

@@ -372,7 +372,7 @@ void iot_mqtt_publish_sensor(void) {
     if (g_iot_state != IOT_STATE_READY) return;
     if (!g_report_cfg.enable) return;
 
-    /* 复用 g_pkg_uart_2 中的传感器帧 */
+    /* Reuse g_pkg_uart_2 sensor frame from Loop MCU */
     if (g_pkg_uart_2.flag == 0) return;
     if (g_pkg_uart_2.pkg[0] != 0x7F) return;
     if (g_pkg_uart_2.pkg[3] != 0xC0) return;
@@ -386,67 +386,75 @@ void iot_mqtt_publish_sensor(void) {
         return;
     }
 
-    /* 构建 loop_data JSON */
-    static char data_json[IOT_MQTT_SEND_BUF_LEN];   // static: 避免栈溢出
-    char *p = data_json;
-    int remaining = sizeof(data_json);
-    int written;
+    /* Batch-publish: 2 channels per message to keep each under 512 bytes.
+       Full-field JSON (freq_current, freq_diff, condition, misc) per the protocol doc. */
+    static char data_json[1024];   // single buffer for 2-channel JSON
+    static char payload[1024];
+    char *pub_topic = (char *)g_iot_topic.topic_pub;
+    uint8_t batch_start = 0;
     uint8_t i;
 
-    written = snprintf(p, remaining,
-        "{\"channels\":[");
-    if (written < 0 || written >= remaining) goto done;
-    p += written; remaining -= written;
-
-    for (i = 0; i < sr.coil_count; i++) {
-        const LUP_CoilSensor *cs = &sr.coils[i];
-        const char *misc_type_str = "time";
-        uint32_t misc_val = 0;
-
-        if (cs->misc_type == 0) { misc_type_str = "time"; misc_val = cs->misc.passtime_ms; }
-        else if (cs->misc_type == 1) { misc_type_str = "cut_count"; misc_val = cs->misc.cut_amount; }
-        else if (cs->misc_type == 2) { misc_type_str = "flow_count"; misc_val = cs->misc.flow_amount; }
-        else if (cs->misc_type == 3) { misc_type_str = "relay_count"; misc_val = cs->misc.relay_count; }
-
-        const char *freq_level_names[] = {"high", "mid_high", "mid_low", "low"};
+    while (batch_start < sr.coil_count) {
+        char *p = data_json;
+        int remaining = sizeof(data_json);
+        int written;
+        uint8_t batch_end = batch_start + 2;
+        if (batch_end > sr.coil_count) batch_end = sr.coil_count;
 
         written = snprintf(p, remaining,
-            "%s{\"ch\":%d,\"fl\":\"%s\",\"car\":%s,"
-            "\"ok\":%s,\"sens\":%d,\"mt\":\"%s\",\"mv\":%lu}",
-            (i > 0) ? "," : "",
-            i + 1,
-            freq_level_names[cs->freq_level],
-            cs->car_state ? "true" : "false",
-            cs->loop_state ? "false" : "true",
-            cs->sensitivity,
-            misc_type_str, misc_val);
+            "{\"channels\":[");
         if (written < 0 || written >= remaining) goto done;
         p += written; remaining -= written;
-    }
 
-    snprintf(p, remaining, "]}");
+        for (i = batch_start; i < batch_end; i++) {
+            const LUP_CoilSensor *cs = &sr.coils[i];
+            const char *misc_type_str = "time";
+            uint32_t misc_val = 0;
 
-    /* 包装为通用消息格式 */
-    static char payload[IOT_MQTT_SEND_BUF_LEN];  // static: 避免 2KB 栈溢出
-    snprintf(payload, sizeof(payload),
-        "{\"msg_id\":%d,\"cmd\":\"loop_data\",\"ts\":%lu,\"data\":%s}",
-        ++g_iot_msg_id, mstick() / 1000, data_json);
+            if (cs->misc_type == 0) { misc_type_str = "time"; misc_val = cs->misc.passtime_ms; }
+            else if (cs->misc_type == 1) { misc_type_str = "cut_count"; misc_val = cs->misc.cut_amount; }
+            else if (cs->misc_type == 2) { misc_type_str = "flow_count"; misc_val = cs->misc.flow_amount; }
+            else if (cs->misc_type == 3) { misc_type_str = "relay_count"; misc_val = cs->misc.relay_count; }
 
-    {
-        uint16_t plen = (uint16_t)strlen(payload);
-        if (plen > 450) {
-            PRINT("IOT: payload too large (%u bytes), skipping\n", plen);
-        } else {
-            /* V1.01: publish to g_iot_topic.topic_pub = dld960/{sn}/dev */
-            char *pub_topic = (char *)g_iot_topic.topic_pub;
-            mqtt_publish(pub_topic, payload, 0);
+            const char *freq_level_names[] = {"high", "mid_high", "mid_low", "low"};
+
+            written = snprintf(p, remaining,
+                "%s{\"ch\":%d,\"freq_level\":\"%s\",\"has_car\":%s,"
+                "\"loop_ok\":%s,\"freq_current\":%lu,\"freq_diff\":%d,"
+                "\"sensitivity\":%d,\"condition\":%d,"
+                "\"misc\":{\"type\":\"%s\",\"value\":%lu}}",
+                (i > batch_start) ? "," : "",
+                i + 1,
+                freq_level_names[cs->freq_level],
+                cs->car_state ? "true" : "false",
+                cs->loop_state ? "false" : "true",
+                cs->freq, cs->variation,
+                cs->sensitivity, cs->condition,
+                misc_type_str, misc_val);
+            if (written < 0 || written >= remaining) goto done;
+            p += written; remaining -= written;
         }
+
+        snprintf(p, remaining, "]}");
+
+        /* Wrap in outer message and publish */
+        snprintf(payload, sizeof(payload),
+            "{\"msg_id\":%d,\"cmd\":\"loop_data\",\"ts\":%lu,\"data\":%s}",
+            ++g_iot_msg_id, mstick() / 1000, data_json);
+
+        uint16_t plen = (uint16_t)strlen(payload);
+        mqtt_publish(pub_topic, payload, 0);
+
+        batch_start = batch_end;
     }
 
 done:
     InitPkgUart(&g_pkg_uart_2);
 }
 
+    InitPkgUart(&g_pkg_uart_2);
+}
+
 /*===========================================================================
  * 心跳上报
  *===========================================================================*/