Ratchet Files

A source file is over budget when it is past what an agent can read in one pass (8,000 tokens, counted as bytes / 4, unless the repository sets another). scripts/check-file-size.mjs owns what counts as source, the budget, the ratchet, and the split rules; run it with --help before anything else.

Splitting

1. Run the script with --all from the repository root, passing the repository's --max-tokens if its hook sets one. Its list is the backlog.
2. Pick the files to split: the one blocking the work in front of you, or with no blocker, the largest ones a change is about to touch.
3. Split each one by the rules the script prints. A seam is a concept the file already owns, not a line count; when refactor-clean is installed, use it to find them.
4. Prove the split changed no behaviour with the repository's own checks, and commit it alone, before the change that needed the room.

A file whose every split would cost more than it saves (one table or state machine that only reads whole) may opt out instead. Put @ratchet-files-ignore in a comment within its first 10 lines, in the file's own comment syntax, followed by why splitting fails:

// @ratchet-files-ignore: one opcode table; split, each half reads without the other.

The check then skips the file entirely, even as it grows, so opt out only after looking for a seam and finding none worth its cost, never to get past a refusal. Tell the user each file you opt out and why. --all counts opted-out files so they stay visible.

Done when every file you picked is under budget in its own commit, the behaviour checks pass, and --all no longer lists those files.

Setting up the ratchet

Never install the hook without the user's explicit yes, even when they asked to set up the repository. Installing it freezes every file already over budget, so audit first and leave the repository untouched while you do:

1. Copy the script to a scratch directory outside the repository, run npm install --prefix <scratch> linguist-languages there, and run node <scratch>/check-file-size.mjs --all from the repository root (Node 18.3 or later). The script finds the package beside itself when the repository lacks it.
2. Ask once, with everything the user is agreeing to: how many files the hook would freeze and which are largest, leaving out generated or vendored ones you will mark below (name those); the budget, 8,000 tokens unless they want another; and which pre-commit runner you will wire it into, including any you would add. In a repository without Node tooling, say the check adds it.

Once they agree, set up everything the check needs:

• Script. The hook runs a copy committed in the repository, so every clone runs the same check. If this skill folder is committed in the repository, point the hook at its scripts/check-file-size.mjs; otherwise copy that file to where the repository keeps its tool scripts (scripts/ if it has none). The entries below use scripts/check-file-size.mjs; substitute the real path.

• Dependency. Add linguist-languages at an exact version as a dev dependency of the repository's root package.json, with the package manager its lockfile names, or npm if there is none. The check needs Node even in a repository written in another language: with no package.json, create one at the root holding only "private": true and what this setup adds, and make sure .gitignore covers node_modules/. Choose dependency versions compatible with the repository's supported runtime; the check script's minimum Node version does not establish the runner's minimum.

• Hook. Run the script on every staged file with node (or bun where the repository already runs its tools with it), appending --max-tokens N for a budget other than the default. Add it beside the existing entries of the pre-commit runner the repository already has:

  Runner	Where	Entry
  lint-staged	its config	"*": "node scripts/check-file-size.mjs"
  lefthook	pre-commit.commands	run: node scripts/check-file-size.mjs {staged_files}
  pre-commit	.pre-commit-config.yaml, repo: local	id: ratchet-files, name: source file size, entry: node scripts/check-file-size.mjs, language: system
  husky or a plain hook	the pre-commit script	git diff --cached --name-only -z | xargs -0 node scripts/check-file-size.mjs

  Inspect git config --show-origin --get core.hooksPath and the existing hooks first. The config is normally shared while a relative path resolves per checkout, so Husky's .husky/_ exists only where the package install ran and every other worktree commits unchecked. Keep an existing runner only if it installs into linked worktrees too.

  Otherwise add lint-staged as an exact dev dependency and call scripts/install-git-hooks.mjs from the root package's prepare script, after any existing prepare work. Use this skill's copy if the skill is committed in the repository, else commit an unchanged copy beside the repository's tool scripts; never point at a global skill path. It installs one hook in the shared hooks directory that runs the committing checkout's own lint-staged, refuses a checkout without dependencies with its lockfile's install command, and leaves custom hooks alone. Each committing worktree needs its own install; never share another checkout's dependencies or build output to provide them. If its logic must change, extend node --test scripts/install-git-hooks.test.mjs from this skill to cover it.

  When replacing a repository-owned runner such as Husky, move its other checks into lint-staged and remove its setup and dependency so no installer competes; never unset a user's own hooks path. Installing an older branch can still re-enable the old runner until a current branch installs again. Inspect any conflict the installer reports before going on.

• Exclusions. Mark generated and vendored code linguist-generated or linguist-vendored in .gitattributes instead of adding skip lists. The script reads the staged .gitattributes, so stage it before rerunning --all.

• Docs. Document the budget, the opt-out pragma, how package installation enables hooks across worktrees, that each committing checkout needs dependencies, and any replaced runner an older branch can re-enable, where the repository documents its other hooks; failing that, in a section of its README, creating one if needed.

Commit the setup through the new hook, without --no-verify.

Verify with real git commit attempts in disposable repository fixtures, using the committed installer, runner configuration, and size-check script. Install once, then create a linked worktree without rerunning installation there. Make its dependencies available and prove its own staged oversized new file is refused with the split rules while an under-budget commit succeeds and the main checkout stays unchanged. Also prove an existing oversized file cannot grow, a checkout without dependencies refuses with setup instructions, repeated installation from a linked worktree works, and custom hooks survive installation. Remove the fixtures afterwards.

Done when these commit checks pass in both checkout types and the setup commit passed the new hook without bypassing it.