Block pushes and commits to main with git hooks

pre-push rejects any push that would update refs/heads/main, however the
command is spelled; pre-commit and pre-merge-commit refuse commits while
main is checked out. npm install enables them via core.hooksPath. The
README documents the three layers of protection for main.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.githooks/pre-commit

@@ -0,0 +1,7 @@
+#!/bin/sh
+# Refuse commits (and, via pre-merge-commit, merge commits) while main is checked out.
+if [ "$(git symbolic-ref --short -q HEAD)" = "main" ]; then
+  echo "$(basename "$0"): committing on main is not allowed; create a branch first." >&2
+  exit 1
+fi
+exit 0

.githooks/pre-merge-commit

@@ -0,0 +1,2 @@
+#!/bin/sh
+exec "$(dirname "$0")/pre-commit"

.githooks/pre-push

@@ -0,0 +1,11 @@
+#!/bin/sh
+# Reject any push that would create, update or delete main on the remote, however the
+# command is spelled (bare `git push`, HEAD:main, +main, refs/heads/main, --all, --mirror).
+# Only a human merges into main, through a PR in Gitea.
+while read -r local_ref local_sha remote_ref remote_sha; do
+  if [ "$remote_ref" = "refs/heads/main" ]; then
+    echo "pre-push: pushing to main is not allowed; push a branch and open a PR instead." >&2
+    exit 1
+  fi
+done
+exit 0

README.md

@@ -3,6 +3,7 @@
 A tiny todo CLI that exists to try out [Claude Code](https://docs.claude.com/en/docs/claude-code) features.
 
 ```sh
+npm install   # once per clone: turns on the git hooks in .githooks/
 npm test
 npm start -- add "try Claude Code"
 npm start -- done 1
@@ -18,6 +19,12 @@ npm start -- ls
 | `.claude/skills/changelog/` | A custom skill — run `/changelog` |
 | `.claude/agents/test-writer.md` | A custom subagent — "use the test-writer agent to…" |
 
+### Protecting `main`
+Changes reach `main` only through a PR that a human merges. Three layers, strongest first:
+1. **Gitea branch protection** on `main` (set in the repo settings on code.westerkam.org): the only layer that can't be bypassed from a clone.
+2. **Git hooks** in `.githooks/` (enabled by `npm install`): `pre-push` rejects any push that would update `main`, however it's spelled; `pre-commit` / `pre-merge-commit` refuse commits while `main` is checked out. `--no-verify` skips them.
+3. **Claude Code deny rules** in `.claude/settings.json` for `git push … main`: a quick early stop, but they match command text, so they're easy to get around.
+
 ## Things to try
 
 - *"There's a bug in how ids are assigned after removing a todo — find it and fix it with a test."*

package.json

@@ -6,7 +6,8 @@
   "bin": { "todo": "./src/cli.js" },
   "scripts": {
     "start": "node src/cli.js",
-    "test": "node --test"
+    "test": "node --test",
+    "prepare": "git config core.hooksPath .githooks"
   },
   "engines": { "node": ">=20" },
   "license": "MIT"

test/hooks.test.js

@@ -0,0 +1,55 @@
+import { test } from "node:test";
+import assert from "node:assert/strict";
+import { spawnSync } from "node:child_process";
+import { mkdtempSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import { fileURLToPath } from "node:url";
+
+const HOOKS = fileURLToPath(new URL("../.githooks/", import.meta.url));
+const SHA = "1".repeat(40);
+const ZERO = "0".repeat(40);
+
+function prePush(...lines) {
+  return spawnSync("sh", [join(HOOKS, "pre-push"), "origin", "git@example:repo.git"], {
+    input: lines.map((l) => l + "\n").join(""),
+    encoding: "utf8",
+  });
+}
+
+function repoOn(branch) {
+  const dir = mkdtempSync(join(tmpdir(), "todo-hooks-"));
+  spawnSync("git", ["init", "-q", "-b", branch, dir]);
+  return dir;
+}
+
+for (const [label, line] of [
+  ["an update", `refs/heads/fix/x ${SHA} refs/heads/main ${SHA}`],
+  ["a new ref", `refs/heads/fix/x ${SHA} refs/heads/main ${ZERO}`],
+  ["a deletion", `(delete) ${ZERO} refs/heads/main ${SHA}`],
+]) {
+  test(`pre-push rejects ${label} of main`, () => {
+    const res = prePush(line);
+    assert.equal(res.status, 1);
+    assert.match(res.stderr, /pushing to main is not allowed/);
+  });
+}
+
+test("pre-push rejects --all style pushes that include main", () => {
+  const res = prePush(`refs/heads/fix/x ${SHA} refs/heads/fix/x ${SHA}`, `refs/heads/main ${SHA} refs/heads/main ${SHA}`);
+  assert.equal(res.status, 1);
+});
+
+test("pre-push allows other branches, including ones named like main", () => {
+  const res = prePush(`refs/heads/fix/x ${SHA} refs/heads/fix/x ${ZERO}`, `refs/heads/maintenance ${SHA} refs/heads/maintenance ${SHA}`);
+  assert.equal(res.status, 0);
+});
+
+for (const hook of ["pre-commit", "pre-merge-commit"]) {
+  test(`${hook} rejects main and allows other branches`, () => {
+    const onMain = spawnSync("sh", [join(HOOKS, hook)], { cwd: repoOn("main"), encoding: "utf8" });
+    assert.equal(onMain.status, 1);
+    assert.match(onMain.stderr, /committing on main is not allowed/);
+    assert.equal(spawnSync("sh", [join(HOOKS, hook)], { cwd: repoOn("fix/x") }).status, 0);
+  });
+}