Implement TextInput component with useInput hook #11769

Parent Epic

Part of #11762 (Ink-based TUI Rewrite)

Objective

Create text input handling using Ink's useInput hook, supporting line editing, history, and keyboard shortcuts.

Current Implementation

The existing input.ts (128 lines) provides LineEditor with:

• Basic text editing (insert, delete, cursor movement)
• Command history (up/down arrows)
• Line submission (Enter)

Approach Options

Option A: Use ink-text-input

import TextInput from 'ink-text-input'

const InputLine = () => {
  const [value, setValue] = useState('')
  return <TextInput value={value} onChange={setValue} onSubmit={handleSubmit} />
}

Option B: Custom implementation with useInput

import { useInput } from 'ink'

const InputLine = () => {
  const [value, setValue] = useState('')
  const [cursor, setCursor] = useState(0)
  
  useInput((input, key) => {
    if (key.return) handleSubmit(value)
    else if (key.backspace) handleBackspace()
    else if (key.leftArrow) moveCursor(-1)
    else if (key.rightArrow) moveCursor(1)
    else if (key.upArrow) historyPrev()
    else if (key.downArrow) historyNext()
    else if (input) insertChar(input)
  })
  
  return <Text>{prompt}{value}</Text>
}

Recommendation: Start with ink-text-input, customize if needed.

Tasks

• Create src/cli/ink/components/InputLine.tsx
• Implement prompt display: agent-name ❯
• Implement text input with cursor
• Implement command history (up/down arrows)
• Implement agent cycling (Shift+Tab)
• Implement cancel (Escape during streaming)
• Implement exit (Ctrl+C)
• Handle multi-line input (if needed)

Keyboard Shortcuts

Acceptance Criteria

• Text input works with cursor display
• History navigation works
• Agent cycling works
• All keyboard shortcuts functional
• Prompt updates when agent changes

Estimated Effort

1.5 days

Risk

Low - ink-text-input handles most complexity

Dependencies

• Setup Ink dependencies and verify Bun compatibility #11763 (Setup Ink dependencies)
• Implement core App component and state management #11764 (App component)