[Mainfurr]

If STA can't connect at boot (for example while the router is rebooting) and sta fallback mode is setup, ESP3D switches to the setup AP and stays there until someone restarts it. This PR adds an opt-in setting so it rejoins on its own once the network is back.

Changes

• New byte setting ESP_STA_FALLBACK_RETRY (position 1257, the first free byte after ESP_USB_SERIAL_BAUD_RATE), shown in [ESP400] as "sta fallback retry" under network/sta. It's no/yes with a default of no, so behaviour is unchanged unless it's turned on.
• When it's on, the radio mode is STA, and the setup AP is running as the STA fallback, WiFiConfig::handle() starts an async scan every 2 minutes (STA_FALLBACK_RETRY_INTERVAL). If the configured SSID shows up, it calls NetConfig::begin(). If that connection fails again, the normal fallback applies.
• No scan runs while a client is connected to the setup AP, because the channel hopping would disrupt it.
• Settings saved by older builds have 0xFF at the new position. ESP3DSettings::begin() replaces an invalid value there with the default.

Testing

• This branch builds for esp32-c3 and esp8266dev.
• The same two commits run on an ESP32-C3 with Marlin, on DevZTH's fork of 3.1.3 (only the base differs). With the extender off, I power-cycled the printer so it came up in setup mode. After the extender was switched back on, the printer rejoined STA by itself.

Limitations

• A hidden SSID never appears in a scan, so it won't be rejoined.
• With a wrong saved password, it retries every 2 minutes, and each attempt briefly drops the setup AP.

[luc-github]

what about AP never show up ? it will scan every 2 min and stay in STA mode without beeing configured again ?

[Mainfurr]

It stays in setup AP mode the whole time and remains configurable at the setup IP. It scans every 2 minutes only while no client is connected to the AP, so configuring isn't disturbed. If you prefer, I can add a limit, e.g. stop after N attempts or back off to longer intervals.

[luc-github]

no need extra settings to keep it simple, but I think it would be good to add an ESP command for it, to disable easily it if necessary and to get the status if connected by serial

[Mainfurr]

Thanks, makes sense. I've added [ESP109] to show or set the rejoin (ON/OFF, set needs admin), and when the setup fallback starts with the rejoin on it now sends "Waiting for STA network" to all clients (serial included), next to the existing "STA network found, reconnecting". No new settings. Docs updated in espXXX.md, Commands.md and authentication.md.

[luc-github]

merged thank you

@all-contributors please add @Mainfurr for code enhancement

[allcontributors]

@luc-github

I've put up a pull request to add @Mainfurr! 🎉