Improve MQTT and WiFi resilience

[Allram]

This PR bundles a few small resilience improvements for running MitsuQTT as a long-lived MQTT bridge. Happy to split it into separate PRs if you'd prefer.

Changes

Grow the MQTT buffer to 1024 bytes. PubSubClient's default MQTT_MAX_PACKET_SIZE is 256 bytes, which the state topic payload (9 fields, ~180–200 bytes serialized) plus topic name sits right up against. With a longer root topic or friendly name, publish() starts returning false and state updates silently stop. Discovery messages were already safe (streamed via beginPublish()), but regular publishes need the buffer.

Reconnect to MQTT with exponential backoff. mqttConnect() previously looped over five blocking connect() attempts, and was re-invoked every second (MQTT_RETRY_INTERVAL_MS). Each connect() against an unreachable broker blocks for seconds, so while the broker was down the main loop was effectively starved — heat pump sync stalled and the web UI became unresponsive. It now makes a single attempt per call, and the caller retries with the same exponential backoff scheme already used for the heat pump connection (1s doubling to a max of ~4 minutes). The manual reconnect button on the status page resets the backoff so it still connects immediately.

Try WiFi.reconnect() before rebooting. Addresses the existing TODO in loop() ("do we really need to reboot here?"): on connection loss the firmware now nudges the WiFi stack every 30 seconds, and keeps the reboot as a last resort after the existing 5-minute deadline. Also sets setAutoReconnect(true) explicitly.

Disable modem power saving. The ESP8266's default modem sleep causes latency spikes and dropped packets with some access points (UniFi APs are a common report). The device is always mains-powered, so the ~tens of mW saved aren't worth it. Uses WiFi.setSleepMode(WIFI_NONE_SLEEP) on ESP8266 and WiFi.setSleep(false) on ESP32.

Mask all password fields in logConfig(). Only ap_pwd was masked; mqtt_pwd, login_password, and ota_pwd were logged in cleartext — and with MQTT logging enabled they end up on the debug topic at the broker.

Testing

• pio test -e test-native passes
• pio run -e WEMOS_D1_Mini builds clean; src/ is clang-format-17 clean
• Flashed on a WEMOS D1 Mini connected to a live Mitsubishi unit — connects to WiFi/MQTT and controls the unit as expected

🤖 Generated with Claude Code

[floatplane]

Thank you @Allram! Waiting for CI to complete and then will merge

I am not actively using this project anymore (moved house and now have Daikin units), so I'll add you as a collaborator so you can make changes without friction. Happy to transfer the project to you as well if you'd prefer!

[Allram]

Thank you @Allram! Waiting for CI to complete and then will merge

I am not actively using this project anymore (moved house and now have Daikin units), so I'll add you as a collaborator so you can make changes without friction. Happy to transfer the project to you as well if you'd prefer!

Thanks for adding me as a collaborator. I run my own private fork with ota updates etc for friends, just wanted to add some changes upstream 👌

[floatplane]

@Allram that's so cool, glad it's working for you!