firmware: migrate cargo controller to LilyGO T-Relay S3

docs/HARDWARE.md

@@ -239,3 +239,30 @@ Important guardrails:
 ## M9N GPS Module
 
 The dashboard enclosure will include an M9N GPS module connected to the ESP32-S3 dashboard over UART. It will provide GPS fix status, satellite count, position, speed, and UTC time. Future work will use GPS time/location for automatic timezone and DST handling.
+
+
+### LilyGO T-Relay-S3 6-relay cargo controller
+
+The cargo ESP now targets the LilyGO T-Relay-S3 6-relay board.
+
+Relay control is handled through the onboard 74HC595 shift register, not direct ESP32 GPIO relay outputs.
+
+| Function | GPIO |
+| --- | --- |
+| 74HC595 DATA | GPIO7 |
+| 74HC595 CLOCK | GPIO5 |
+| 74HC595 LATCH | GPIO6 |
+| 74HC595 nOE | GPIO4 |
+
+| Firmware ID | LilyGO relay channel | Shift-register output |
+| --- | --- | --- |
+| relay_1 | CH1 | SR1 |
+| relay_2 | CH2 | SR2 |
+| relay_3 | CH3 | SR3 |
+| relay_4 | CH4 | SR4 |
+| relay_5 | CH5 | SR5 |
+| relay_6 | CH6 | SR6 |
+
+GPIO4 is reserved for relay output-enable on this board, so the DS18B20 OneWire bus is moved to GPIO14.
+
+Avoid GPIO35-GPIO37 on the LilyGO T-Relay-S3 because they are used by Octal SPI flash.

docs/cargo-api-contract.md

@@ -157,7 +157,7 @@ Expected output object fields:
 Example 2-channel profile:
 
     {
-      "hardware_profile": "generic_esp32_2ch_relay",
+      "hardware_profile": "lilygo_t_relay_s3_6ch",
       "outputs": [
         {"id": 1, "name": "Fridge", "role": "fridge", "hardware_channel": 1},
         {"id": 2, "name": "Starlink", "role": "starlink", "hardware_channel": 2}
@@ -190,7 +190,7 @@ The Cargo ESP firmware now exposes relay/output state as an output-count-agnosti
 
 The current active hardware profile remains:
 
-    generic_esp32_2ch_relay
+    lilygo_t_relay_s3_6ch
 
 The API includes:
 

docs/project-state.md

@@ -270,7 +270,7 @@ The Cargo ESP API now represents relays/outputs as a hardware-profile-aware list
 
 Current active hardware profile:
 
-    generic_esp32_2ch_relay
+    lilygo_t_relay_s3_6ch
 
 Future planned profile:
 

docs/roadmap.md

@@ -213,3 +213,13 @@ Rationale:
 - Improves perceived responsiveness without a major communication rewrite.
 - Supports future live gauges better than fixed-interval polling.
 
+
+
+## LilyGO T-Relay-S3 6-relay migration
+
+- [x] Expand cargo relay model from 2 outputs to 6 outputs.
+- [x] Replace direct GPIO relay writes with LilyGO 74HC595 shift-register writes.
+- [x] Map relay_1 through relay_6 to CH1 through CH6.
+- [x] Move DS18B20 OneWire default from GPIO4 to GPIO14 because GPIO4 is relay nOE.
+- [ ] Bench test relay boot behavior with no vehicle loads connected.
+- [ ] Confirm CH1-CH6 order with a meter or test lamp before wiring vehicle loads.