[aripiprazole]

Purpose

Running bun run check needs exact tool versions. With Bun 1.3.13, the frozen install fails and 10 tests fail. This PR gives everyone the same tools, and lints each commit before it reaches CI.

• flake.nix: nix develop (or direnv allow once, via .envrc) gives a shell with Bun 1.4.2, Node 24 and Python 3.
  • Everything comes from stable nixos-26.05 except Bun. Stable ships Bun 1.3.13 and the project pins 1.4.2, so Bun alone comes from nixos-unstable.
• Pre-commit hook: entering the shell installs it, through git-hooks.nix. It runs Biome and nixfmt.
  • It uses the project's own Biome (node_modules/.bin/biome), so it always formats like CI does. Nix's Biome (2.4.15) is a different version from the project's 2.4.16.
  • It fixes what it can and fails the commit if anything changed.
  • It doesn't run ESLint or tsc, which are slow. bun run check still runs them in CI.
• .zed/settings.json:
  • Biome formats on save and organizes imports. Zed takes Biome from node_modules, so it uses the pinned version.
  • nil and nixfmt for Nix files run from the shell through direnv exec.
• CI: bun pm pack --dry-run replaces npm pack --dry-run.
• .direnv/ and the generated .pre-commit-config.yaml are gitignored. Without that, Biome follows the config link and fails to parse it.

Verification

All run inside nix develop:

• bun install --frozen-lockfile and bun run check pass, including all 121 tests and the build.
• bun pm pack --dry-run lists 20 files.
• pre-commit run --all-files passes Biome and nixfmt.
• On a staged, badly formatted .ts file, the hook rewrites it and fails the commit.