[Feature] Text input widget

[vmarcella]

Overview

Add a text input widget for single-line text entry with cursor and selection.

Current State

No response

Scope

Goals:

• Single-line text entry
• Cursor positioning with click
• Keyboard input handling
• Text selection (shift+arrow)
• Copy/paste support

Non-Goals:

• Multi-line text area
• Rich text editing
• Input validation

Proposed API

pub struct TextInput {
  text: String,
  cursor_position: usize,
  selection_start: Option<usize>,
  placeholder: Option<String>,
  on_change: Option<Box<dyn Fn(&str)>>,
  on_submit: Option<Box<dyn Fn(&str)>>,
}

impl TextInput {
  pub fn new() -> Self;
  pub fn with_placeholder(self, text: &str) -> Self;
  pub fn on_change(self, callback: impl Fn(&str) + 'static) -> Self;
  pub fn on_submit(self, callback: impl Fn(&str) + 'static) -> Self;
  pub fn text(&self) -> &str;
  pub fn set_text(&mut self, text: &str);
  pub fn clear(&mut self);
}

impl Widget for TextInput {
  fn render(&self, ctx: &mut UiRenderContext) -> Vec<RenderCommand>;
}

Acceptance Criteria

• Text entry works with keyboard
• Cursor visible and blinking
• Click positions cursor
• Arrow keys move cursor
• Selection with shift+arrows
• Enter key triggers submit
• Placeholder shows when empty

Affected Crates

lambda-rs

Notes

• Handle Ctrl+A (select all), Ctrl+C/V (copy/paste)
• Clipboard requires platform integration