feat(ms-ai-architect): add lib/cross-platform-paths for cache/log/state/backup dirs [skip-docs]

First foundation lib for v1.12.0 auto-KB-update. Resolves per-OS paths:
- macOS: ~/Library/{Caches,Logs,Application Support}/<app>/
- Linux: XDG_CACHE_HOME / XDG_STATE_HOME with ~/.cache, ~/.local/state fallbacks
- Windows: %LOCALAPPDATA%\<app>\{Cache,Logs,State}

Plus getBackupDir(pluginRoot) → <pluginRoot>/.kb-backup (gitignored).

All four functions auto-mkdir target. Dependency-injection via opts
({platform, homedir, env}) makes the lib pure-testable; 13/13 tests
pass under tmpdir isolation without touching real ~/ paths.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

plugins/ms-ai-architect/tests/kb-update/test-cross-platform-paths.test.mjs

@@ -0,0 +1,129 @@
+// tests/kb-update/test-cross-platform-paths.test.mjs
+// Unit tests for scripts/kb-update/lib/cross-platform-paths.mjs
+// Zero deps. Uses node:test + dependency-injection (homedir/platform overrides) to avoid filesystem and OS coupling.
+
+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+import { mkdtempSync, rmSync, existsSync, statSync } from 'node:fs';
+import { tmpdir } from 'node:os';
+import { join } from 'node:path';
+import {
+  getCacheDir,
+  getLogDir,
+  getStateDir,
+  getBackupDir,
+} from '../../scripts/kb-update/lib/cross-platform-paths.mjs';
+
+const APP = 'ms-ai-architect-test';
+
+function withTmp(fn) {
+  const dir = mkdtempSync(join(tmpdir(), 'cpp-test-'));
+  try {
+    return fn(dir);
+  } finally {
+    rmSync(dir, { recursive: true, force: true });
+  }
+}
+
+test('getCacheDir — macOS returns ~/Library/Caches/<app>/', () => {
+  withTmp((home) => {
+    const result = getCacheDir(APP, { platform: 'darwin', homedir: () => home, env: {} });
+    assert.equal(result, join(home, 'Library', 'Caches', APP));
+    assert.equal(existsSync(result), true);
+    assert.equal(statSync(result).isDirectory(), true);
+  });
+});
+
+test('getCacheDir — Linux uses XDG_CACHE_HOME when set', () => {
+  withTmp((home) => {
+    const xdg = join(home, 'custom-cache');
+    const result = getCacheDir(APP, { platform: 'linux', homedir: () => home, env: { XDG_CACHE_HOME: xdg } });
+    assert.equal(result, join(xdg, APP));
+    assert.equal(existsSync(result), true);
+  });
+});
+
+test('getCacheDir — Linux falls back to ~/.cache/<app>/ when no XDG', () => {
+  withTmp((home) => {
+    const result = getCacheDir(APP, { platform: 'linux', homedir: () => home, env: {} });
+    assert.equal(result, join(home, '.cache', APP));
+  });
+});
+
+test('getCacheDir — Windows uses %LOCALAPPDATA%\\<app>\\Cache', () => {
+  withTmp((home) => {
+    const lad = join(home, 'AppData', 'Local');
+    const result = getCacheDir(APP, { platform: 'win32', homedir: () => home, env: { LOCALAPPDATA: lad } });
+    assert.equal(result, join(lad, APP, 'Cache'));
+  });
+});
+
+test('getLogDir — macOS returns ~/Library/Logs/<app>/', () => {
+  withTmp((home) => {
+    const result = getLogDir(APP, { platform: 'darwin', homedir: () => home, env: {} });
+    assert.equal(result, join(home, 'Library', 'Logs', APP));
+  });
+});
+
+test('getLogDir — Linux uses XDG_STATE_HOME/<app>/logs when set', () => {
+  withTmp((home) => {
+    const xdg = join(home, 'custom-state');
+    const result = getLogDir(APP, { platform: 'linux', homedir: () => home, env: { XDG_STATE_HOME: xdg } });
+    assert.equal(result, join(xdg, APP, 'logs'));
+  });
+});
+
+test('getLogDir — Linux falls back to ~/.local/state/<app>/logs/', () => {
+  withTmp((home) => {
+    const result = getLogDir(APP, { platform: 'linux', homedir: () => home, env: {} });
+    assert.equal(result, join(home, '.local', 'state', APP, 'logs'));
+  });
+});
+
+test('getLogDir — Windows uses %LOCALAPPDATA%\\<app>\\Logs', () => {
+  withTmp((home) => {
+    const lad = join(home, 'AppData', 'Local');
+    const result = getLogDir(APP, { platform: 'win32', homedir: () => home, env: { LOCALAPPDATA: lad } });
+    assert.equal(result, join(lad, APP, 'Logs'));
+  });
+});
+
+test('getStateDir — macOS uses ~/Library/Application Support/<app>/', () => {
+  withTmp((home) => {
+    const result = getStateDir(APP, { platform: 'darwin', homedir: () => home, env: {} });
+    assert.equal(result, join(home, 'Library', 'Application Support', APP));
+  });
+});
+
+test('getStateDir — Linux uses XDG_STATE_HOME when set', () => {
+  withTmp((home) => {
+    const xdg = join(home, 'custom-state');
+    const result = getStateDir(APP, { platform: 'linux', homedir: () => home, env: { XDG_STATE_HOME: xdg } });
+    assert.equal(result, join(xdg, APP));
+  });
+});
+
+test('getBackupDir — joins pluginRoot and .kb-backup, creates if missing', () => {
+  withTmp((root) => {
+    const result = getBackupDir(root);
+    assert.equal(result, join(root, '.kb-backup'));
+    assert.equal(existsSync(result), true);
+    assert.equal(statSync(result).isDirectory(), true);
+  });
+});
+
+test('default options — uses real os.homedir() and process.platform', () => {
+  // Smoke-test: with no overrides, returns something sane (creates dir under real home).
+  // Use an unusual app name to avoid colliding with anything real.
+  const APP_REAL = 'ms-ai-architect-cpp-smoke-' + process.pid;
+  const result = getCacheDir(APP_REAL);
+  assert.ok(result.length > 0);
+  assert.equal(existsSync(result), true);
+  // Cleanup
+  rmSync(result, { recursive: true, force: true });
+});
+
+test('getCacheDir — throws on missing app name', () => {
+  assert.throws(() => getCacheDir(), /appName/);
+  assert.throws(() => getCacheDir(''), /appName/);
+});