chore(typescript): add biome musl performance repro

[Swimburger]

Description

Refs: Devin run | Requested by @Swimburger

Adds a minimal, self-contained reproduction for a ~15x Biome performance regression when running on Alpine Linux (musl libc). This is intended to be shared with the Biome team as a bug report.

Changes Made

• Added repros/biome-musl-perf/ directory containing:
  • Dockerfile — Alpine-based image (musl, slow)
  • Dockerfile.debian — Debian-based image (glibc, fast)
  • benchmark.sh — Automated comparison script (native vs Alpine vs Debian)
  • sdk/ — 322 TypeScript files from the trace seed SDK, biome.json config, and a minimal package.json with only @biomejs/biome as a dependency
  • README.md — Full write-up with benchmark results and reproduction steps
• Added !!repros/** exclusion to root biome.jsonc to prevent conflict between the repo's root biome config and the repro's own biome.json (which must have "root": true to function as a standalone repro)

Key Finding

Environment	Biome self-reported time	Libc
Native Linux (host)	119ms	glibc
Docker Debian (node:22-bookworm-slim)	119ms	glibc
Docker Alpine (node:22-alpine3.20)	1731ms	musl

The slowdown is musl-specific, not Docker overhead — the Debian container matches native. Likely caused by musl's memory allocator interacting poorly with Rust binaries (Biome is written in Rust).

Testing

• Verified biome check runs in ~119ms natively
• Verified biome check runs in ~1731ms in Alpine Docker
• Verified biome check runs in ~119ms in Debian Docker (confirming musl as root cause)

Review Checklist

• Is repros/ an acceptable directory for this, or should it live in a separate repo/gist for the Biome issue?
• The repro includes ~322 generated TypeScript source files (~1.6 MB). Acceptable for the repo, or too much?
• Note: no .gitignore inside repros/biome-musl-perf/ — node_modules could be accidentally committed if someone runs pnpm install locally. Consider adding one.
• The benchmark script labels the host as "glibc" which may not always be accurate.
• The !!repros/** exclusion in biome.jsonc means any future code under repros/ will be excluded from the repo-wide biome check. Acceptable as a blanket exclusion, or should it be scoped to !!repros/biome-musl-perf/**?

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