chore: scope pre-commit formatting to staged files

[tallyhuhu]

Summary

Scope the pre-commit Biome run to staged source and test files only.

Motivation

The previous hook ran Biome with --write across the full src and tests trees on every commit. This could rewrite unrelated files outside the staged change, leaving noisy working-tree modifications after a focused commit.

Changes

• collect staged files with git diff --cached --name-only --diff-filter=ACMR
• filter to JS/TS files under src/ and tests/
• skip the hook when no matching files are staged
• run pnpm exec biome check --write only on matching staged files
• re-add formatted files before the commit continues

Safety

This only changes local commit tooling. Runtime client behavior and public APIs are unchanged.

Testing

• committed this hook-only change and verified the hook exits without formatting the full repository
• verified no unrelated files were modified after commit

---

Note

Low Risk
Only affects local developer tooling and the commit path; no runtime or production code changes, with limited risk of friction from the new partially-staged-file guard.

Overview
Updates the Husky pre-commit hook to run Biome formatting only on staged JS/TS files under src/ and tests/, and to no-op when no matching files are staged.

The hook now blocks commits with partially staged matching files (to avoid formatting divergence), then runs pnpm exec biome check --write on the staged file list and re-stages any formatting changes.

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