Add root --skill flag printing the bundled skill text

[schacon]

but --skill writes the bundled base skill text (SKILL.md) to stdout and exits, so agents can load the GitButler skill into context directly (e.g. but --skill >> prompt.md) without installing skill files first.

What changed

• New root-only --skill flag on Args. It short-circuits right after argument parsing, like --version: but --skill prints the skill even if a subcommand follows, and but status --skill is rejected since the flag is not global.
• The output reuses the installer's prepare_skill_content path via a new command::skill::base_skill_text(), so the CLI version is injected into the frontmatter exactly as but skill install writes it, and the embedded file is UTF-8 validated.
• Output is raw stdout — no pager, truncation, or output-channel formatting — so it pipes cleanly.
• but skill --help long help now cross-references but --skill for discoverability.

Decisions

• Only SKILL.md is printed, not the references/ files; the flag targets bootstrap/context-loading, where the base skill is the entry point.
• The bundled skill docs themselves don't mention the flag: an agent that already has the skill installed has no use for printing it.

Testing

Integration test asserts but --skill output equals the embedded SKILL.md with the version swapped in, deriving the expected version from but --version so it holds for both dev and release builds.

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[Copilot]

Pull request overview

Adds a new root-only --skill flag to the but CLI that prints the bundled SKILL.md (with the CLI version injected) to stdout and exits, enabling agents/users to easily load the GitButler skill text into context via piping/redirection.

Changes:

• Added a new top-level --skill flag and short-circuit execution path to print the bundled base skill text and exit.
• Exposed command::skill::base_skill_text() to reuse the existing skill content preparation/version-injection logic.
• Added an integration test asserting but --skill output matches the bundled SKILL.md with the runtime --version injected, and updated but skill --help docs to reference the flag.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
crates/but/src/args/mod.rs	Adds the root-only --skill flag and updates skill subcommand help text to reference it.
crates/but/src/lib.rs	Implements early-exit behavior that prints the skill text when --skill is set.
crates/but/src/command/skill/mod.rs	Introduces base_skill_text() to produce version-injected SKILL.md content for --skill.
crates/but/tests/but/command/skill.rs	Adds an integration test validating but --skill output against the bundled SKILL.md with version injection.

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[krlvi]

Since we already have a but skill command, how about this being but skill show?

[Copilot]

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated no new comments.

Suppressed comments (2)

crates/but/src/lib.rs:297

• but --skill writes via print!, which bypasses the CLI’s usual broken-pipe suppression (see OutputChannel’s write_str handling). For pipe-friendly behavior (e.g. but --skill | head), write to stdout and explicitly ignore ErrorKind::BrokenPipe instead of using print!.

    // Like `--version`, `--skill` prints and exits without dispatching a subcommand.
    if args.skill {
        print!("{}", command::skill::base_skill_text()?);
        return Ok(());
    }

crates/but/src/command/skill/mod.rs:984

• command::skill is exported as a public module (crates/but/src/command/mod.rs), so making base_skill_text pub expands the crate’s public API surface. Since it’s only used internally by handle_args, it should likely be pub(crate) to avoid committing to it as a supported API.

/// The bundled base skill text (SKILL.md) with the CLI version injected,
/// as printed by `but --skill`.
pub fn base_skill_text() -> Result<String> {
    prepare_skill_content(option_env!("VERSION").unwrap_or("dev"))
}