feat(cli): add /md command to render markdown files

[mvanhorn]

Summary

Adds a /md <file> slash command to the interactive CLI session. Reads a markdown file and renders it in the terminal using the existing print_markdown function (bat-based syntax highlighting, table extraction, theme support).

Changes

• crates/goose-cli/src/session/input.rs: Added /md <path> handler in handle_slash_command(). Reads the file with std::fs::read_to_string, renders via print_markdown_for_command, returns InputResult::Retry to re-show the prompt.
• crates/goose-cli/src/session/output.rs: Added pub fn print_markdown_for_command(content: &str) wrapper that calls print_markdown with the current theme from get_theme().
• crates/goose-cli/src/session/completion.rs: Added /md to the slash command completion list.

Error handling: prints "Error reading : " for missing/unreadable files. Shows "Usage: /md " for empty path.

Testing

Verified via cargo clippy and cargo fmt. The implementation reuses existing, tested infrastructure (print_markdown, get_theme, InputResult::Retry pattern).

Fixes #8249

This contribution was developed with AI assistance (Codex).

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Match bare /md command before requiring an argument

The new slash-command branch only matches s.starts_with("/md "), so entering /md without a trailing space does not hit this handler and is treated as a normal chat message (InputResult::Message) instead of showing the intended usage/retry path. This causes an unintended model request whenever a user types /md directly (or removes the auto-inserted space), so the command parser should explicitly handle the exact /md token as invalid usage.

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[michaelneale]

thanks @mvanhorn - do you want to sign the DCO so we can get this in? also - we are moving to ui/text for the TUI, may be worth considering there.

[mvanhorn]

Signed both commits and force-pushed. Also added a fix for bare /md (without a trailing space) falling through to chat instead of showing usage.

Good to know about the ui/text move for the TUI. Happy to port this there if that's the preferred path, or keep it in the current CLI layer if it still makes sense here.

[DOsinga]

Hey @mvanhorn, thanks for the contribution! I'm going to close this one out for a couple of reasons:

1. Multiple open PRs: It looks like you have 5 open PRs with none merged yet — our contributing guide asks that first-time contributors wait for earlier PRs to land before opening more, so reviewers can give each one proper attention. See: https://github.com/block/goose/blob/main/CONTRIBUTING.md#pull-requests

2. Feature direction: After some discussion we've decided we don't really need a /md slash command in goose right now, so we're also closing the linked issue.

We really do appreciate you taking the time to contribute though! If you'd like to keep working with us, we'd suggest picking one of your existing PRs to focus on and we can go from there. 🙏

[mvanhorn]

Totally fair, thanks for explaining. I'll focus on getting #8271 across the line first and pace future submissions better.