TankSync v3.6.9

A diagnostics and correctness release. No behaviour changes to tank
measurement, LoRa, or sleep.

Fixed: hub OTA failures now say what went wrong

The hub reported a bare "Download failed" for three completely different
problems — a transfer error, a truncated image, or a validation failure
at the end. The detail existed but only ever reached the serial console,
so a hub on a shelf could tell you it failed and nothing more.

The status now names the stage and carries the underlying error, so an
OTA problem can be diagnosed over the network.

Fixed: receiver version stamping

Receiver-ESP32-DevKit was still stamped 3.6.7 while shipping inside the
v3.6.8 release, so the hub reported a different version than the release
it came from. Both products now stamp the release version.

Included from v3.6.8

Firmware for the 3.3 V transmitter board, and correct battery reporting
on transmitters built without an INA219. See the v3.6.8 notes for detail
on choosing between the 5 V and 3.3 V images.

Upgrading

Hubs update over the air. Transmitters flash over USB — pick the image
matching your board revision.

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Downloads (every variant for this firmware version)

Transmitter — ESP32-C3 SuperMini

• …-transmitter-lora-esp32c3-<tag>.bin — LoRa SKU (RYLR998 module)
• …-transmitter-lite-espnow-esp32c3-<tag>.bin — Lite SKU (ESP-NOW, built-in radio, no module)

Receiver / Hub

• …-receiver-esp32-<tag>.bin — ESP32 DevKit
• …-receiver-esp32s3-<tag>.bin — ESP32-S3 SuperMini

Each variant ships two images:

• plain .bin — OTA app image, flash at 0x10000, or use the one-click browser flasher / in-app OTA.
• …-full.bin — full-flash image for a fresh/blank board, flash at 0x0 with esptool: esptool.py write_flash 0x0 <file>-full.bin.