fix: pass arguments to commands without explicit placeholders

[remorses]

Fixes#9587

Arguments passed to custom commands were silently ignored if the command template didn't include $1, $2, or $ARGUMENTS placeholders. Also adds support for multi-line input after commands.

Context: https://x.com/__morse/status/2003830333205323835

Users coming from other tools expect to pass extra content after a command and have it appended to the prompt, like:

/review
focus on security issues

Previously this extra content was silently dropped unless the command explicitly used $ARGUMENTS. Now commands without placeholders will automatically receive user arguments appended to the template.

Changes:

• TUI: Parse command from first line only, preserve newlines in arguments
• Backend: Auto-append arguments to template if command has no placeholders

[github-actions]

Thanks for your contribution!

This PR doesn't have a linked issue. All PRs must reference an existing issue.

Please:

1. Open an issue describing the bug/feature (if one doesn't exist)
2. Add Fixes #<number> or Closes #<number> to this PR description

See CONTRIBUTING.md for details.

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Based on my search, I found one potentially related PR:

Related PR:

• Feat: custom commands #1304 - "Feat: custom commands" (Feat: custom commands #1304)
  • This appears to be the original feature implementation for custom commands. PR fix: pass arguments to commands without explicit placeholders #9606 is fixing an issue with how arguments are passed to these custom commands when placeholders aren't explicitly defined.

No duplicate/competing fixes for this specific issue were found. The search results show #9606 is the only PR addressing the argument passing fix.

[Copilot]

Pull request overview

This PR enables custom commands without placeholders to automatically receive user arguments, addressing the feature request in #9587. Previously, arguments were silently discarded if a command template didn't include $1, $2, or $ARGUMENTS placeholders.

Changes:

• Modified TUI to parse commands from the first line only and preserve multi-line content in arguments
• Added backend logic to auto-append arguments to command templates when no placeholders are present
• Removed debug console.log statement

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
packages/opencode/src/cli/cmd/tui/component/prompt/index.tsx	Updated command parsing to extract command from first line only and preserve newlines in subsequent argument lines
packages/opencode/src/session/prompt.ts	Added logic to detect commands without placeholders and automatically append user arguments to the template

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