unstable/cli: excess positional arguments are silently discarded instead of failing

[chenxin-yan]

Version: effect 4.0.0-beta.101

What happens

The parser silently drops positional arguments that no declared param consumes, and no combinator can make it fail:

import { Command, Argument } from "effect/unstable/cli"

// Command with no arguments:
const init = Command.make("init", {})
// `mycli init extra` succeeds — "extra" is silently ignored

// Command with a single positional:
const run = Command.make("run", { prompt: Argument.string("prompt") })
// `mycli run "hi" oops` succeeds with prompt = "hi" — "oops" is silently ignored

// Cardinality combinators don't help:
Argument.string("prompt").pipe(Argument.between(1, 1)) // or atMost(1)
// max only stops consuming; the extra positional is still silently dropped

Cause

• internal/command.js parseParams threads currentArguments through each declared param and discards whatever remains after the loop — there is no "unexpected argument" check.
• Param.js parsePositionalVariadic enforces min with an error but treats max purely as a stop-consuming bound.

Why this looks like a bug

• Asymmetric with flags: unknown flags raise UnrecognizedOption, and parseOptionVariadic fails with InvalidValue when occurrences exceed max — positionals do neither.
• Regression from v3: stable @effect/cli documented a ValidationError for excess arguments.

Suggested fix

Fail the parse when positionals remain unconsumed after parseParams, and/or make positional max reject extras the way flag max does.