Add legacy open-source caching module as default

Recover the pre-extraction caching code (from 7a4e0968~1) into a
standalone module at sources/legacy-caching/. This module bundles
@actions/cache@4.0.5 with the existing patch and adapts the old
caching API to the current CacheService interface.

The cache-service-loader now uses the legacy module by default and
only loads the proprietary vendored module when the license is
accepted. Both paths are wrapped in a LoggingCacheService that
identifies which module is active in logs and the Job Summary.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

sources/legacy-caching/src/index.ts

@@ -0,0 +1,41 @@
+import * as core from '@actions/core'
+import * as os from 'os'
+
+import {CacheConfig, CacheOptions} from './cache-config-adapter'
+import {BuildResult, BuildResults} from './build-results-adapter'
+import {CacheListener, generateCachingReport} from './cache-reporting'
+import {DaemonController} from './daemon-controller'
+import * as caches from './caches'
+
+const CACHE_LISTENER_STATE_KEY = 'legacy-cache-listener'
+
+export async function restore(gradleUserHome: string, cacheOptions: CacheOptions): Promise<void> {
+    const userHome = os.homedir()
+    const cacheListener = new CacheListener()
+    const cacheConfig = new CacheConfig(cacheOptions)
+
+    await caches.restore(userHome, gradleUserHome, cacheListener, cacheConfig)
+
+    // Persist the listener so it can be rehydrated in save()
+    core.saveState(CACHE_LISTENER_STATE_KEY, cacheListener.stringify())
+}
+
+export async function save(
+    gradleUserHome: string,
+    buildResults: BuildResult[],
+    cacheOptions: CacheOptions
+): Promise<string> {
+    const userHome = os.homedir()
+    const cacheConfig = new CacheConfig(cacheOptions)
+
+    // Rehydrate the listener from the restore phase
+    const listenerState = core.getState(CACHE_LISTENER_STATE_KEY)
+    const cacheListener = CacheListener.rehydrate(listenerState)
+
+    const buildResultsWrapper = new BuildResults(buildResults)
+    const daemonController = new DaemonController(buildResultsWrapper)
+
+    await caches.save(userHome, gradleUserHome, cacheListener, daemonController, buildResultsWrapper, cacheConfig)
+
+    return generateCachingReport(cacheListener)
+}