[FEATURE] Expose embedded Bun runtime for skill scripts

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

Claude Code's native binary (installed via curl, Homebrew, or WinGet) ships with Bun embedded as a standalone executable. Skills can bundle and run scripts in any language, but there is no guaranteed runtime available for executing those scripts.

When a skill bundles a TypeScript or JavaScript file and the SKILL.md instructs Claude to run it, Claude invokes bun run script.ts or node script.ts via Bash. But:

• Native install users (the majority, and the recommended install path) have Bun embedded inside the claude binary but no bun or node on their PATH.
• npm install users have Node.js by definition, but this install method is being deprecated.
• Non-technical users — the growing audience Anthropic is targeting — have no idea how to install a language runtime, and shouldn't have to.

Proposed Solution

The Bun runtime is already there inside the Claude Code binary. Exposing it for skill execution would make bundled scripts work for every user out of the box.

Alternative Solutions

. BUN_BE_BUN=1 claude — Works today with native installs, but it's an undocumented Bun feature, not a Claude Code contract. Could break at any time. Doesn't work with npm installs. Non-technical users wouldn't know to set this.

1. npx -y bun script.ts — Bootstraps Bun via npm. But native install users don't necessarily have npm/Node on their PATH either, which defeats the whole point.

1. Bash-only scripts — The only runtime you can reasonably assume exists (on macOS/Linux). But bash is terrible for anything complex, and doesn't exist on Windows without WSL.

1. Python scripts — Anthropic's own skills (like skill-creator) assume Python is available. It's pre-installed on macOS and most Linux distros, but not guaranteed on Windows, and version mismatches are common. Still the most pragmatic option today.

1. Have the SKILL.md instruct Claude to write/generate code inline — Avoids needing a runtime for pre-bundled scripts, but sacrifices determinism. The whole point of bundling scripts is repeatable, reliable execution rather than hoping Claude regenerates correct code each time.

1. Skill preprocessor (` !command `) — Runs shell commands before the skill prompt is sent to Claude, but still requires whatever runtime the command needs.

1. Distributing compiled binaries per platform — Completely impractical for skill authors.

Priority

High - Significant impact on productivity

Feature Category

CLI commands and flags

Use Case Example

I'm building a skill that generates a visual dependency graph of a codebase as an interactive HTML file. The skill bundles a TypeScript script under scripts/analyze-deps.ts that walks the file tree, parses imports, and outputs a JSON structure that gets fed into a templated HTML file.

The script needs to be deterministic and reliable — it does AST parsing, cycle detection, and file I/O that would be fragile and inconsistent if left to Claude to regenerate each time. So it's bundled as a pre-written script, exactly as the skills documentation recommends.

This isn't a niche concern — it affects every skill that bundles executable code, which is a core pattern in the skills documentation. Even Anthropic's own skill-creator skill assumes Python is available.

Additional Context

_No response_