Update batch schema and add ACK handling

README.md

@@ -45,7 +45,6 @@ Variants:
   - Energy total: 1-0:1.8.0*255
   - Total power: 1-0:16.7.0*255
   - Phase power: 36.7 / 56.7 / 76.7
-  - Phase voltage: 32.7 / 52.7 / 72.7
 - Reads battery voltage and estimates SoC.
 - Builds JSON payload, compresses, wraps in LoRa packet, transmits.
 - Light sleeps between meter reads; batches are sent every 30s.
@@ -56,11 +55,11 @@ Variants:
 **Sender flow (pseudo-code)**:
 ```cpp
 void sender_loop() {
-  meter_read_every_second(); // SML/OBIS -> MeterData samples
+  meter_read_every_second(); // OBIS -> MeterData samples
   read_battery(data);        // VBAT + SoC
 
   if (time_to_send_batch()) {
-    json = meterBatchToJson(samples);
+    json = meterBatchToJson(samples, batch_id);
     compressed = compressBuffer(json);
     lora_send(packet(MeterBatch, compressed));
   }
@@ -77,7 +76,7 @@ void sender_loop() {
 
 **Key sender functions**:
 ```cpp
-bool meter_read(MeterData &data);        // parse SML frame, set OBIS fields
+bool meter_read(MeterData &data);        // parse OBIS fields
 void read_battery(MeterData &data);      // ADC -> volts + percent
 bool meterDataToJson(const MeterData&, String&);
 bool compressBuffer(const uint8_t*, size_t, uint8_t*, size_t, size_t&);
@@ -89,6 +88,7 @@ bool lora_send(const LoraPacket &pkt);   // add header + CRC16 and transmit
 - NTP sync (UTC) and local display in Europe/Berlin.
 - Receives LoRa packets, verifies CRC16, decompresses, parses JSON.
 - Publishes meter JSON to MQTT.
+- Sends ACKs for MeterBatch packets and de-duplicates by batch_id.
 - Web UI:
   - AP mode: status + WiFi/MQTT config.
   - STA mode: status + per-sender pages.
@@ -169,7 +169,7 @@ Packet layout:
 [0]    protocol_version (1)
 [1]    role (0=sender, 1=receiver)
 [2..3] device_id_short (uint16)
-[4]    payload_type (0=meter, 1=test, 2=time_sync, 3=meter_batch)
+[4]    payload_type (0=meter, 1=test, 2=time_sync, 3=meter_batch, 4=ack)
 [5..N-3] compressed payload
 [N-2..N-1] CRC16 (bytes 0..N-3)
 ```
@@ -190,14 +190,38 @@ JSON payload (sender + MQTT):
   "p1_w": 500.00,
   "p2_w": 450.00,
   "p3_w": 0.00,
-  "v1_v": 230.10,
-  "v2_v": 229.80,
-  "v3_v": 231.00,
   "bat_v": 3.92,
   "bat_pct": 78
 }
 ```
 
+MeterBatch JSON (compressed over LoRa) uses per-field arrays with integer units for easier ingestion:
+
+```json
+{
+  "schema": 1,
+  "sender": "s01",
+  "batch_id": 1842,
+  "t0": 1738288000,
+  "dt_s": 1,
+  "n": 3,
+  "energy_wh": [123456700, 123456701, 123456701],
+  "p_w": [930, 940, 950],
+  "p1_w": [480, 490, 500],
+  "p2_w": [450, 450, 450],
+  "p3_w": [0, 0, 0],
+  "meta": {
+    "rssi": -92,
+    "snr": 7.5,
+    "rx_ts": 1738288031
+  }
+}
+```
+
+Notes:
+- `sender` maps to `EXPECTED_SENDER_IDS` order (`s01` = first sender).
+- `meta` is injected by the receiver after batch reassembly.
+
 ## Device IDs
 - Derived from WiFi STA MAC.
 - `short_id = (MAC[4] << 8) | MAC[5]`
@@ -253,12 +277,20 @@ inline constexpr uint16_t EXPECTED_SENDER_IDS[NUM_SENDERS] = { 0xF19C };
 - `lilygo-t3-v1-6-1-868`: production build for 868 MHz modules
 - `lilygo-t3-v1-6-1-868-test`: test build for 868 MHz modules
 
+## Config Knobs
+Key timing settings in `include/config.h`:
+- `METER_SAMPLE_INTERVAL_MS`
+- `METER_SEND_INTERVAL_MS`
+- `BATCH_ACK_TIMEOUT_MS`
+- `BATCH_MAX_RETRIES`
+
 ## Limits & Known Constraints
 - **Compression**: uses lightweight RLE (good for JSON but not optimal).
-- **OBIS parsing**: supports IEC 62056-21 ASCII (Mode D) and SML; may need tuning for some meters.
+- **OBIS parsing**: supports IEC 62056-21 ASCII (Mode D); may need tuning for some meters.
 - **Payload size**: single JSON frames < 256 bytes (ArduinoJson static doc); batch frames are chunked and reassembled.
 - **Battery ADC**: uses simple linear calibration constant in `power_manager.cpp`.
 - **OLED**: no hardware reset line is used (matches working reference).
+- **Batch ACKs**: sender waits for ACK after a batch and retries up to `BATCH_MAX_RETRIES` with `BATCH_ACK_TIMEOUT_MS` between attempts.
 
 ## Files & Modules
 - `include/config.h`, `src/config.cpp`: pins, radio settings, sender IDs
@@ -266,7 +298,7 @@ inline constexpr uint16_t EXPECTED_SENDER_IDS[NUM_SENDERS] = { 0xF19C };
 - `include/json_codec.h`, `src/json_codec.cpp`: JSON encode/decode
 - `include/compressor.h`, `src/compressor.cpp`: RLE compression
 - `include/lora_transport.h`, `src/lora_transport.cpp`: LoRa packet + CRC
-- `include/meter_driver.h`, `src/meter_driver.cpp`: IEC 62056-21 ASCII + SML parse
+- `include/meter_driver.h`, `src/meter_driver.cpp`: IEC 62056-21 ASCII parse
 - `include/power_manager.h`, `src/power_manager.cpp`: ADC + sleep
 - `include/time_manager.h`, `src/time_manager.cpp`: NTP + time sync
 - `include/wifi_manager.h`, `src/wifi_manager.cpp`: NVS config + WiFi