Problem

@effect/cli currently has a hard split between boolean flags and value-accepting options:

• Options.boolean — never consumes a value (--watch)
• Options.text / Options.choice — always require a value (--watch=mode)

There's no way to define an option that works as both a standalone flag and a value-accepting option. This is a common CLI pattern — e.g. --color vs --color=always in GNU tools, --watch vs --watch=mode in various dev tools.

Desired behavior

A flag like --watch that:

• When absent → Option.none
• When bare (--watch) → defaults to a specified value (e.g. 'first-failure')
• When explicit (--watch=until-done) → uses the provided value

Possible API

const watch = Options.choice('watch', ['first-failure', 'until-done']).pipe(
  Options.withOptionalValue('first-failure'), // bare --watch → 'first-failure'
  Options.optional, // absent → Option.none
)

Or alternatively:

const watch = Options.boolean('watch').pipe(
  Options.withOptionalValue(Options.choice(['first-failure', 'until-done']), 'first-failure'),
)

Prior art

• GNU coreutils: --color[=WHEN]
• TypeScript compiler: --watch
• Vitest / Jest: --watch vs --watch=mode
• Python argparse: nargs='?' with const for the bare-flag default

Filed on behalf of @schickling