Implement SelectMenu component #11770

Parent Epic

Part of #11762 (Ink-based TUI Rewrite)

Objective

Create selection menu component for agent selection, model selection, and other choices.

Current Implementation

The existing select.ts (122 lines) provides:

• Arrow key navigation
• Enter to select
• Escape to cancel
• Scrolling for long lists

Component Design

import { Box, Text, useInput } from 'ink'

interface SelectMenuProps<T> {
  items: Array<{ label: string; value: T }>
  onSelect: (value: T) => void
  onCancel?: () => void
  title?: string
}

const SelectMenu = <T,>({ items, onSelect, onCancel, title }: SelectMenuProps<T>) => {
  const [selected, setSelected] = useState(0)
  
  useInput((input, key) => {
    if (key.upArrow) setSelected(s => Math.max(0, s - 1))
    if (key.downArrow) setSelected(s => Math.min(items.length - 1, s + 1))
    if (key.return) onSelect(items[selected].value)
    if (key.escape && onCancel) onCancel()
  })
  
  return (
    <Box flexDirection="column">
      {title && <Text bold>{title}</Text>}
      {items.map((item, i) => (
        <Text key={i} color={i === selected ? 'cyan' : undefined}>
          {i === selected ? '❯ ' : '  '}{item.label}
        </Text>
      ))}
    </Box>
  )
}

Tasks

• Create src/cli/ink/components/SelectMenu.tsx
• Implement arrow key navigation
• Implement selection highlight
• Implement Enter to confirm
• Implement Escape to cancel
• Handle long lists (scrolling/pagination)
• Support search/filter (optional)

Use Cases

1. Agent selection (/agent command)
2. Model selection (/model command)
3. Session selection (/sessions command)
4. Confirmation dialogs

Acceptance Criteria

• Navigation works with arrow keys
• Selection highlight visible
• Enter confirms selection
• Escape cancels
• Works with varying list lengths

Estimated Effort

0.5 days

Risk

Low - straightforward component

Dependencies

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