cli: invalid directory arg shows raw ENOENT chdir stack trace instead of friendly error

Summary

Running opencode <unknown-arg> treats the arg as <directory> and prints a raw ENOENT ... chdir error with an internal Bun stack trace (/$bunfs/root/chunk-*.js) instead of a friendly validation error. Exit code is still 0.

Environment

• opencode version: 2.0.7
• OS: Linux arch 6.18.49-3-lts #1 SMP PREEMPT_DYNAMIC Sun, 06 Sep 2026 13:22:39 +0000 x86_64 GNU/Linux
• Terminal: TERM=xterm-256color, COLORTERM=truecolor, TERM_PROGRAM=unset
• Shell: /bin/bash
• Install/channel: latest (npm-opencode-cli via mise: ~/.local/share/mise/installs/npm-opencode-cli/latest), update: disable in config
• Active plugins: global MCP servers context7, exa, kaggle enabled, chrome-devtools disabled; CLI plugin ./herdr-opencode; no project-local opencode.json(c) found

Reproduction

1. Open a shell in a directory without a ./ls entry (e.g. ~).
2. Run opencode ls.
3. Observe the error output.
4. Same result with opencode foobar123 and opencode /nonexistent-dir-xyz.

Expected Behavior

Friendly validation error such as directory 'ls' does not exist plus usage hint (opencode <subcommand> [flags] [<directory>] / opencode --help), with non-zero exit code. No internal paths in output.

Actual Behavior

Raw error log with internal stack frame, exit 0:

~ ❯ opencode ls
[08:36:57.084] ERROR (#1): Error: ENOENT: no such file or directory, chdir '/home/broto' -> 'ls'
    at chdir (unknown)
    at <anonymous> (/$bunfs/root/chunk-3vv35md2.js:96:6419)

opencode --help confirms USAGE: opencode <subcommand> [flags] [<directory>] with no ls subcommand, so the arg falls through to <directory> and fails in chdir.

Additional Context

• Consistently reproducible (3/3 tries: ls, foobar123, /nonexistent-dir-xyz).
• opencode --help lists subcommands: upgrade, uninstall, acp, api, debug, auth, mcp, plugin, models, stats, mini, run, session, service, reload, pair, serve.
• Workaround: run opencode --help to check valid subcommands; pass only existing directories as positional arg.
• No secrets included; MCP API keys redacted from config.