feat(sync): complete incremental sync protocol with storage-pull, state management, and tests (#799)

- Add storage-pull strategy: rclone-based sync from remote storage with
  overlay and clean modes, URI parsing (storage://remote:bucket/path),
  transfer parallelism, and automatic rclone availability checking
- Add SyncStateManager: persistent state load/save with configurable
  paths, workspace hash calculation via SHA-256 of key project files,
  and drift detection for external modification awareness
- Add action.yml inputs: syncStrategy, syncInputRef, syncStorageRemote,
  syncRevertAfter, syncStatePath with sensible defaults
- Wire sync into Input (5 getters), BuildParameters (5 fields), index.ts
  (local build path), and RemoteClient (orchestrator path) with post-job
  overlay revert when syncRevertAfter is true
- Add 42 unit tests covering all strategies, URI parsing, state
  management, hash calculation, drift detection, error handling, and
  edge cases (missing rclone, invalid URIs, absent state, empty diffs)
- Add root:true to eslintrc to prevent plugin resolution conflicts

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/index.ts

@@ -3,6 +3,8 @@ import { Action, BuildParameters, Cache, Orchestrator, Docker, ImageTag, Output
 import { Cli } from './model/cli/cli';
 import MacBuilder from './model/mac-builder';
 import PlatformSetup from './model/platform-setup';
+import { IncrementalSyncService } from './model/orchestrator/services/sync';
+import { SyncStrategy } from './model/orchestrator/services/sync/sync-state';
 
 async function runMain() {
   try {
@@ -23,6 +25,14 @@ async function runMain() {
 
     if (buildParameters.providerStrategy === 'local') {
       core.info('Building locally');
+
+      // Apply incremental sync strategy before build
+      const syncStrategy = buildParameters.syncStrategy as SyncStrategy;
+      if (syncStrategy !== 'full') {
+        core.info(`[Sync] Applying sync strategy: ${syncStrategy}`);
+        await applySyncStrategy(buildParameters, workspace);
+      }
+
       await PlatformSetup.setup(buildParameters, actionFolder);
       exitCode =
         process.platform === 'darwin'
@@ -32,6 +42,16 @@ async function runMain() {
               actionFolder,
               ...buildParameters,
             });
+
+      // Revert overlays after job completion if configured
+      if (buildParameters.syncRevertAfter && syncStrategy !== 'full') {
+        core.info('[Sync] Reverting overlay changes after job completion');
+        try {
+          await IncrementalSyncService.revertOverlays(workspace, buildParameters.syncStatePath);
+        } catch (revertError) {
+          core.warning(`[Sync] Overlay revert failed: ${(revertError as Error).message}`);
+        }
+      }
     } else {
       await Orchestrator.run(buildParameters, baseImage.toString());
       exitCode = 0;
@@ -50,4 +70,58 @@ async function runMain() {
   }
 }
 
+/**
+ * Apply the configured sync strategy to the workspace before build.
+ */
+async function applySyncStrategy(buildParameters: BuildParameters, workspace: string): Promise<void> {
+  const strategy = buildParameters.syncStrategy as SyncStrategy;
+  const resolvedStrategy = IncrementalSyncService.resolveStrategy(strategy, workspace, buildParameters.syncStatePath);
+
+  if (resolvedStrategy === 'full') {
+    core.info('[Sync] Resolved to full sync (no incremental state available)');
+
+    return;
+  }
+
+  switch (resolvedStrategy) {
+    case 'git-delta': {
+      const targetReference = buildParameters.gitSha || buildParameters.branch;
+      const changedFiles = await IncrementalSyncService.syncGitDelta(
+        workspace,
+        targetReference,
+        buildParameters.syncStatePath,
+      );
+      core.info(`[Sync] Git delta sync applied: ${changedFiles} file(s) changed`);
+      break;
+    }
+    case 'direct-input': {
+      if (!buildParameters.syncInputRef) {
+        throw new Error('[Sync] direct-input strategy requires syncInputRef to be set');
+      }
+      const overlays = await IncrementalSyncService.applyDirectInput(
+        workspace,
+        buildParameters.syncInputRef,
+        buildParameters.syncStorageRemote || undefined,
+        buildParameters.syncStatePath,
+      );
+      core.info(`[Sync] Direct input applied: ${overlays.length} overlay(s)`);
+      break;
+    }
+    case 'storage-pull': {
+      if (!buildParameters.syncInputRef) {
+        throw new Error('[Sync] storage-pull strategy requires syncInputRef to be set');
+      }
+      const pulledFiles = await IncrementalSyncService.syncStoragePull(workspace, buildParameters.syncInputRef, {
+        rcloneRemote: buildParameters.syncStorageRemote || undefined,
+        syncRevertAfter: buildParameters.syncRevertAfter,
+        statePath: buildParameters.syncStatePath,
+      });
+      core.info(`[Sync] Storage pull complete: ${pulledFiles.length} file(s)`);
+      break;
+    }
+    default:
+      core.warning(`[Sync] Unknown sync strategy: ${resolvedStrategy}`);
+  }
+}
+
 runMain();