esp32-debug-dongle → LilyGo T3-S3 debug bridge

Why

USB serial to the trough/solartrack sensors drops on every deep sleep, so we can't watch boots/crashes/wakes. This dongle becomes an always-connected box on the LAN that bridges a sensor's UART to telnet + a web terminal, controls GPIO to reset/wake the target, logs to SD, and (Phase 2) sniffs the MeshCore LoRa mesh — so we can debug remotely and stop flying blind.

Decisions (confirmed with user)

Board: LilyGo T3-S3 (ESP32-S3 + SX127x LoRa + SSD1306 128×64 OLED + SD). Chosen over TTGO for onboard SD and LoRa (mesh monitoring).
Extend esp32-debug-dongle in place (not a new Sh3dNb app). Keep the existing esp32dev env working; add a t3s3 env.
Both telnet (:23) and the WebSocket terminal. Telnet is the primary remote control path (nc/minicom + an agent driving it); GPIO reset/wake and port/baud are exposed as both telnet ~commands and REST endpoints.
SD logging in Phase 1, ON by default once NTP (built-in configTzTime) gives today's date — log file named/stamped from real time.
Power monitoring: out of scope.
Phase 2: MeshCore monitor over the onboard LoRa (passive RX of mesh packets, surfaced on telnet/web/SD).

Board facts that shape the build

ESP32-S3 has no Bluetooth Classic → BluetoothSerial/SerialBT is guarded behind HAS_BT_CLASSIC (esp32dev only). On T3-S3, telnet + WebSocket replace it.
USB CDC on boot (-DARDUINO_USB_CDC_ON_BOOT=1) → UART0 (GPIO43/44) is free for the target bridge.
Pins (from Sh3dNb/apps_oglas/lilygot3s3_basic): OLED SDA18/SCL17/RST21@0x3C; LoRa SCK5/MISO3/MOSI6/CS7/RST8/DIO0:9; BTN0.

Phase 1 (this build) — extend src/main.cpp + platformio.ini

platformio.ini: keep [env:esp32dev] (+ -DHAS_BT_CLASSIC=1); add [env:t3s3] (esp32-s3-devkitc-1, USB CDC on boot, huge_app, littlefs, Adafruit SSD1306+GFX). All pins via build flags (target UART, GPIO reset/wake, SD, OLED) so they're config, not hardcoded.
Target UART bridge: Serial1 on TARGET_RX/TX pins ↔ fan-out to WebSocket (existing), telnet clients, and SD log. RX/TX byte+line counters.
Telnet server :23 with line protocol: non-~ lines forward to the target UART; ~ lines are commands: ~help ~status ~reset [ms] ~wake [ms] ~baud <n> ~port <int|usb|ext> ~log on|off ~gpio <pin> <0|1>. Lets an operator (or agent via nc) drive a remote board.
REST (mirror of the commands): /api/status /api/reset /api/wake /api/baud?baud= /api/log?on= /api/gpio?pin=&val= /api/send?data=.
GPIO control: configurable reset/wake pins (active-low option), pulse.
NTP + SD logging: configTzTime(<TZ>); once time syncs, open /logs/YYYYMMDD-HHMMSS.log and append timestamped serial. Logging ON by default; ~log off / REST toggles. Graceful no-op if SD absent/pins wrong.
OLED: IP/SSID/RSSI, target pins+baud, RX/TX counts, telnet client count, logging on/off, NTP synced y/n.

Phase 2 — MeshCore monitor (later)

Bring up the T3-S3 LoRa radio (confirm chip: SX1276 vs SX1262 variant) with the mesh's PHY (freq/SF/BW/CR matching the sensors), RX-only.
Decode/forward MeshCore channel frames to telnet/web/SD so we see beacons (e.g. count trough beacons to confirm the sleep-crash fix) without a sensor.

Pins to CONFIRM against the actual board (set as build flags)

SD: SCK/MISO/MOSI/CS for the T3-S3 SD slot (may share the LoRa SPI bus + own CS — verify). Logging silently disables if wrong.
Target UART bridge RX/TX (default UART0 43/44, free under USB CDC).
GPIO reset/wake pins to whatever lines you wire to the sensor's RST/control.
LoRa chip variant (Phase 2).

Verify

pio run -e t3s3 compiles; pio run -e esp32dev still compiles (BT intact).
Flash T3-S3: OLED shows IP; nc <ip> 23 streams a wired sensor's UART; ~reset reboots it (seen on the same stream); a dated file appears under /logs on the SD and grows.

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