Persist remaining client state in disk cache files

Move templates, notifications, backups, table columns, peer envs, and
sidebar/first-connect prefs onto ~/.config/peardock/cache (settings.json
or dedicated JSON files) with legacy localStorage migration.

test/json-cache.test.js

@@ -0,0 +1,102 @@
+/**
+ * File-backed JSON cache under ~/.config/peardock/cache/
+ */
+import test from 'brittle'
+import fs from 'fs'
+import os from 'os'
+import path from 'path'
+import {
+  loadJsonCache,
+  saveJsonCache,
+  clearJsonCache,
+  getCacheFilePath,
+  parseCachePayload,
+  buildCachePayload,
+  JSON_CACHE_VERSION,
+} from '../client/jsonCache.js'
+
+function installLocalStorage() {
+  /** @type {Map<string, string>} */
+  const map = new Map()
+  globalThis.localStorage = {
+    get length() {
+      return map.size
+    },
+    key(i) {
+      return [...map.keys()][i] ?? null
+    },
+    getItem(k) {
+      return map.has(k) ? map.get(k) : null
+    },
+    setItem(k, v) {
+      map.set(String(k), String(v))
+    },
+    removeItem(k) {
+      map.delete(k)
+    },
+    clear() {
+      map.clear()
+    },
+  }
+  return map
+}
+
+function withTempHome(t) {
+  const tmp = fs.mkdtempSync(path.join(os.tmpdir(), 'peardock-json-cache-'))
+  const prev = process.env.PEARDOCK_HOME
+  process.env.PEARDOCK_HOME = tmp
+  t.teardown(() => {
+    if (prev === undefined) delete process.env.PEARDOCK_HOME
+    else process.env.PEARDOCK_HOME = prev
+    try {
+      fs.rmSync(tmp, { recursive: true, force: true })
+    } catch {
+      // ignore
+    }
+  })
+  return tmp
+}
+
+test('build/parse cache envelope', (t) => {
+  const env = buildCachePayload({ a: 1 })
+  t.is(env.version, JSON_CACHE_VERSION)
+  t.ok(env.updatedAt)
+  t.alike(env.data, { a: 1 })
+  t.alike(parseCachePayload(JSON.stringify(env)), { a: 1 })
+  t.alike(parseCachePayload({ flat: true }), { flat: true })
+  t.alike(parseCachePayload([1, 2]), [1, 2])
+})
+
+test('save and load json cache file', (t) => {
+  withTempHome(t)
+  installLocalStorage()
+
+  const r = saveJsonCache('templates', { web: { image: 'nginx' } })
+  t.ok(r.ok)
+  t.ok(fs.existsSync(getCacheFilePath('templates')))
+
+  const loaded = loadJsonCache('templates', { fallback: {} })
+  t.alike(loaded, { web: { image: 'nginx' } })
+})
+
+test('migrates legacy localStorage key into cache file', (t) => {
+  withTempHome(t)
+  const ls = installLocalStorage()
+  ls.set('peardock_templates', JSON.stringify({ old: { image: 'busybox' } }))
+
+  const loaded = loadJsonCache('templates', {
+    fallback: {},
+    legacyLocalStorageKey: 'peardock_templates',
+  })
+  t.alike(loaded, { old: { image: 'busybox' } })
+  t.ok(fs.existsSync(getCacheFilePath('templates')))
+})
+
+test('clearJsonCache removes file', (t) => {
+  withTempHome(t)
+  installLocalStorage()
+  saveJsonCache('notifications', [{ id: '1' }])
+  t.ok(fs.existsSync(getCacheFilePath('notifications')))
+  clearJsonCache('notifications', { legacyLocalStorageKey: 'peardock_notifications' })
+  t.absent(fs.existsSync(getCacheFilePath('notifications')))
+})