feat(lua): enable serial terminal scripts (port query, textEdit placeholder, Enter key)

[graycoderep]

Summary of changes:

These three changes all came out of writing a Lua app that turns the radio into
a serial terminal for any device with a text CLI over UART (flight controllers,
ESCs, GPS modules) through a port set to LUA mode. Each removes a concrete
obstacle. They are technically independent, but the app needs all three, so they
are kept together rather than split into PRs that could land partially.

What this is worth in practice: out in the field it turns hardware the pilot is
already holding into one more tool, with no laptop involved. Connecting to a
UART correctly is the whole setup. And the moment radios gain USB host support,
the very same app does exactly this over an ordinary USB-C cable to the flight
controller, with no wiring at all - so the groundwork here keeps paying off.

1. feat(lua): new serialGetLuaPort()

A script using serialRead()/serialWrite() had no way to find out whether any
serial port is actually set to LUA mode. Without it a script can only sit there
receiving nothing, unable to tell the user why. Returns the port number and its
name, or nil when no port is in LUA mode.

2. feat(color): custom placeholder on text edit fields

An empty text field always renders as ---, both in the field itself and as the
text area placeholder while editing. That is right for settings screens but
wrong for free-form input, where an empty field should simply look empty. The
default is unchanged, so no existing screen is affected; scripts can pass
placeholder = "" (or hint text) to lvgl.textEdit.

3. fix(color): keyboard Enter key does nothing on single-line fields

For a one-line text area LVGL sends LV_EVENT_READY only to the text area,
while the OK checkmark also sends it to the keyboard object - and the keyboard
object is what EdgeTX listens on. The result is that the Enter key neither
commits the value nor closes the keyboard: it does nothing at all, on every
single-line field in the radio.

The Enter key is now detected on the keyboard and routed through a new
FormField::onEnter(), so it commits and closes like the checkmark. A field may
additionally install an enter handler to treat Enter as "submit" as opposed to
the checkmark's "keep editing"; lvgl.textEdit exposes this as an enter
callback, which is what lets the terminal app send a typed command on Enter.

There are no local changes to the vendored LVGL.

Testing:

• Built for X10/TX16S and flashed to a TX16S MK2; the Lua app using all four
  additions runs on the radio.
• Behaviour verified against a real flight controller (IFLIGHT BLITZ F722,
  Betaflight 2025.12.5) on a UART with Configuration/MSP: # opens the CLI,
  commands echo and answer, and the keyboard Enter change commits/sends as
  expected.
• The placeholder default is unchanged in code ("---"), so existing screens
  keep their current appearance; the new behaviour only applies to fields that
  pass the parameter.

Summary by CodeRabbit

• New Features

  • Added configurable placeholder text for text-entry fields.
  • Pressing Enter can now submit a field and trigger a configured action.
  • Lua text-edit widgets support placeholder text and Enter callbacks.
  • Added a Lua API to identify the serial port configured for Lua communication.

• Bug Fixes

  • Text fields now correctly display their configured placeholder when empty.

[coderabbitai]

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: ce07091a-5c31-488b-8115-78563c2a28bb

📥 Commits

Reviewing files that changed from the base of the PR and between 19aa6d5 and 0232fd2.

📒 Files selected for processing (8)

• radio/src/gui/colorlcd/libui/form.h
• radio/src/gui/colorlcd/libui/keyboard_base.cpp
• radio/src/gui/colorlcd/libui/keyboard_base.h
• radio/src/gui/colorlcd/libui/textedit.cpp
• radio/src/gui/colorlcd/libui/textedit.h
• radio/src/lua/api_general.cpp
• radio/src/lua/lua_lvgl_widget.cpp
• radio/src/lua/lua_lvgl_widget.h

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📝 Walkthrough

Walkthrough

The PR adds Enter-key submission to color LCD text fields, configurable text-edit placeholders and Lua Enter callbacks, plus a Lua API for querying the Lua-mode serial port.

Changes

Color LCD text-edit Enter flow

Layer / File(s)	Summary
Form and keyboard Enter submission radio/src/gui/colorlcd/libui/form.h, radio/src/gui/colorlcd/libui/keyboard_base.*	FormField exposes an Enter callback, while Keyboard detects Enter, hides without cancellation, and invokes the callback during cleanup.
TextEdit placeholder and keyboard wiring radio/src/gui/colorlcd/libui/textedit.*	TextEdit supports configurable placeholders and forwards overlay Enter events to onEnter().
Lua text-edit properties and callback radio/src/lua/lua_lvgl_widget.*	Lua text-edit widgets accept placeholder and enter properties, manage the callback reference, and invoke it with bounded text.
Lua serial port discovery radio/src/lua/api_general.cpp	Adds serialGetLuaPort() to return the configured Lua-mode port, or nil when no such port exists.

Sequence Diagram(s)

sequenceDiagram
  participant TextArea
  participant Keyboard
  participant TextEdit
  participant LuaCallback
  TextArea->>Keyboard: detect Enter button
  Keyboard->>Keyboard: hide without cancellation
  Keyboard->>TextEdit: invoke onEnter during field cleanup
  TextEdit->>LuaCallback: call enter callback with bounded text

Loading

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 62.50% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly matches the main change: Lua serial-terminal support via port query, placeholder, and Enter-key handling.
Description check	✅ Passed	The description includes the required summary of changes and testing details, with only the optional Fixes # section omitted.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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[graycoderep]

@coderabbitai summary

Note: the walkthrough/summary is stale — it still mentions LUA_SERIAL_READ_CHUNK and "revised serial read buffering", but that commit was dropped in a force-push. This PR now only adds serialGetLuaPort(), a text-edit placeholder, and keyboard Enter handling; it does not change serial read buffering. Please regenerate.

[coderabbitai]

@graycoderep Thanks for the correction. I will regenerate the PR summary for the current diff. The regenerated summary must exclude LUA_SERIAL_READ_CHUNK and all serial read buffering changes.

✅ Action performed

Summary regeneration triggered.

[coderabbitai]

@graycoderep Thanks for the correction. I will regenerate the PR summary. The regenerated summary must exclude LUA_SERIAL_READ_CHUNK and all serial read buffering changes.

✅ Action performed

Summary regeneration triggered.