Add commit message normalizer hook and install script

- scripts/normalize-commit-msg.js: capitalizes subject, strips trailing
  period, trims whitespace, warns when subject > 72 chars
- scripts/commit-msg: shell wrapper symlinked into .git/hooks/commit-msg
- scripts/install-hooks.sh: contributor setup script (sh scripts/install-hooks.sh)
- scripts/package.json: test runner + hooks:install npm script
- scripts/__tests__/normalize-commit-msg.test.js: 15 unit tests

Nightshift-Task: commit-normalize
Nightshift-Ref: https://github.com/marcus/nightshift

scripts/__tests__/normalize-commit-msg.test.js

@@ -0,0 +1,90 @@
+import { describe, it, expect } from 'vitest';
+const { normalizeSubject, normalizeMessage } = require('../normalize-commit-msg.js');
+
+describe('normalizeSubject', () => {
+  it('passes an already-valid subject unchanged', () => {
+    const { subject, warned } = normalizeSubject('Add feature flag support');
+    expect(subject).toBe('Add feature flag support');
+    expect(warned).toBe(false);
+  });
+
+  it('capitalizes the first letter', () => {
+    const { subject } = normalizeSubject('add feature flag support');
+    expect(subject).toBe('Add feature flag support');
+  });
+
+  it('strips a trailing period', () => {
+    const { subject } = normalizeSubject('Add feature flag support.');
+    expect(subject).toBe('Add feature flag support');
+  });
+
+  it('trims leading whitespace', () => {
+    const { subject } = normalizeSubject('  Fix the bug');
+    expect(subject).toBe('Fix the bug');
+  });
+
+  it('trims trailing whitespace', () => {
+    const { subject } = normalizeSubject('Fix the bug   ');
+    expect(subject).toBe('Fix the bug');
+  });
+
+  it('capitalizes and strips period together', () => {
+    const { subject } = normalizeSubject('fix the bug.');
+    expect(subject).toBe('Fix the bug');
+  });
+
+  it('does not strip a period that is not trailing', () => {
+    const { subject } = normalizeSubject('Fix bug in v1.0 release');
+    expect(subject).toBe('Fix bug in v1.0 release');
+  });
+
+  it('warns when subject exceeds 72 characters', () => {
+    const long = 'A'.repeat(73);
+    const { warned } = normalizeSubject(long);
+    expect(warned).toBe(true);
+  });
+
+  it('does not warn when subject is exactly 72 characters', () => {
+    const exact = 'A'.repeat(72);
+    const { warned } = normalizeSubject(exact);
+    expect(warned).toBe(false);
+  });
+
+  it('does not warn when subject is under 72 characters', () => {
+    const { warned } = normalizeSubject('Short message');
+    expect(warned).toBe(false);
+  });
+
+  it('handles an empty subject gracefully', () => {
+    const { subject, warned } = normalizeSubject('');
+    expect(subject).toBe('');
+    expect(warned).toBe(false);
+  });
+});
+
+describe('normalizeMessage', () => {
+  it('normalizes only the subject line of a multi-line message', () => {
+    const input = 'fix the bug.\n\nThis is the body paragraph.';
+    const { message } = normalizeMessage(input);
+    expect(message).toBe('Fix the bug\n\nThis is the body paragraph.');
+  });
+
+  it('skips comment lines when finding the subject', () => {
+    const input = '# Comment\nfix the bug.';
+    const { message } = normalizeMessage(input);
+    expect(message).toBe('# Comment\nFix the bug');
+  });
+
+  it('returns warned true for long subject inside full message', () => {
+    const longSubject = 'x'.repeat(73);
+    const input = `${longSubject}\n\nBody.`;
+    const { warned } = normalizeMessage(input);
+    expect(warned).toBe(true);
+  });
+
+  it('preserves body lines exactly as-is', () => {
+    const input = 'Fix bug\n\n  - detail one\n  - detail two.';
+    const { message } = normalizeMessage(input);
+    expect(message).toBe('Fix bug\n\n  - detail one\n  - detail two.');
+  });
+});

scripts/commit-msg

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+#!/bin/sh
+# Git commit-msg hook — delegates to normalize-commit-msg.js
+# This file is symlinked into .git/hooks/commit-msg by scripts/install-hooks.sh
+node "$(git rev-parse --show-toplevel)/scripts/normalize-commit-msg.js" "$1"

scripts/install-hooks.sh

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+#!/bin/sh
+# install-hooks.sh
+# Installs the project's git hooks into .git/hooks/.
+# Run this once after cloning: sh scripts/install-hooks.sh
+
+set -e
+
+REPO_ROOT="$(git rev-parse --show-toplevel)"
+HOOKS_DIR="$REPO_ROOT/.git/hooks"
+SCRIPTS_DIR="$REPO_ROOT/scripts"
+
+install_hook() {
+  local name="$1"
+  local src="$SCRIPTS_DIR/$name"
+  local dst="$HOOKS_DIR/$name"
+
+  if [ ! -f "$src" ]; then
+    echo "install-hooks: source not found: $src" >&2
+    return 1
+  fi
+
+  if [ -f "$dst" ] && [ ! -L "$dst" ]; then
+    echo "install-hooks: warning: $dst already exists and is not a symlink — skipping"
+    return 0
+  fi
+
+  ln -sf "$src" "$dst"
+  chmod +x "$src"
+  echo "install-hooks: installed $name -> $dst"
+}
+
+install_hook "commit-msg"
+
+echo "install-hooks: done"

scripts/normalize-commit-msg.js

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+#!/usr/bin/env node
+/**
+ * normalize-commit-msg.js
+ *
+ * Git commit-msg hook: reads the commit message file, applies normalization
+ * rules to the subject line, rewrites the file in place.
+ *
+ * Rules:
+ *   1. Trim leading/trailing whitespace from the subject line
+ *   2. Capitalize the first letter of the subject
+ *   3. Strip a trailing period from the subject
+ *   4. Warn (but do not block) if the subject exceeds 72 characters
+ */
+
+'use strict';
+
+const fs = require('fs');
+
+const MAX_SUBJECT_LEN = 72;
+
+/**
+ * Normalize the subject line of a commit message.
+ * Returns { subject, warned } where warned is true if a length warning was emitted.
+ *
+ * @param {string} subject
+ * @returns {{ subject: string, warned: boolean }}
+ */
+function normalizeSubject(subject) {
+  let s = subject.trimEnd();
+
+  // Trim leading whitespace
+  s = s.trimStart();
+
+  // Capitalize first letter
+  if (s.length > 0) {
+    s = s[0].toUpperCase() + s.slice(1);
+  }
+
+  // Strip trailing period
+  if (s.endsWith('.')) {
+    s = s.slice(0, -1);
+  }
+
+  const warned = s.length > MAX_SUBJECT_LEN;
+
+  return { subject: s, warned };
+}
+
+/**
+ * Normalize a full commit message string.
+ * Only the subject line (first non-empty, non-comment line) is modified.
+ *
+ * @param {string} message
+ * @returns {{ message: string, warned: boolean }}
+ */
+function normalizeMessage(message) {
+  const lines = message.split('\n');
+  let warned = false;
+
+  // Find the subject line (first non-comment line)
+  for (let i = 0; i < lines.length; i++) {
+    const line = lines[i];
+    if (!line.startsWith('#')) {
+      const result = normalizeSubject(line);
+      lines[i] = result.subject;
+      warned = result.warned;
+      break;
+    }
+  }
+
+  return { message: lines.join('\n'), warned };
+}
+
+// Only run as a hook when invoked directly (not when required in tests)
+if (require.main === module) {
+  const msgFile = process.argv[2];
+  if (!msgFile) {
+    process.stderr.write('commit-msg hook: no message file argument\n');
+    process.exit(1);
+  }
+
+  const original = fs.readFileSync(msgFile, 'utf8');
+  const { message, warned } = normalizeMessage(original);
+
+  if (warned) {
+    process.stderr.write(
+      `commit-msg warning: subject line exceeds ${MAX_SUBJECT_LEN} characters — consider shortening it.\n`
+    );
+  }
+
+  fs.writeFileSync(msgFile, message, 'utf8');
+  process.exit(0);
+}
+
+module.exports = { normalizeSubject, normalizeMessage };

scripts/package.json

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+{
+  "name": "budget-scripts",
+  "version": "1.0.0",
+  "scripts": {
+    "test": "vitest run",
+    "test:watch": "vitest",
+    "hooks:install": "sh install-hooks.sh"
+  },
+  "devDependencies": {
+    "vitest": "^4.1.0"
+  }
+}