fix(ci): Remove buildx cache and add preflight enforcement

- Remove cache_from/cache_to from CI (plugin bug splitting commas)
- Add preflight() method to CrawlRotator - tests proxy + anti-detect
- Add pre-task preflight check - workers MUST pass before executing
- Add releaseTask() to release tasks back to pending on preflight fail
- Rename proxy_test task to whoami for clarity

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/src/tasks/task-worker.ts

@@ -59,7 +59,7 @@ import { handleProductDiscovery } from './handlers/product-discovery';
 import { handleStoreDiscovery } from './handlers/store-discovery';
 import { handleEntryPointDiscovery } from './handlers/entry-point-discovery';
 import { handleAnalyticsRefresh } from './handlers/analytics-refresh';
-import { handleProxyTest } from './handlers/proxy-test';
+import { handleWhoami } from './handlers/whoami';
 
 const POLL_INTERVAL_MS = parseInt(process.env.POLL_INTERVAL_MS || '5000');
 const HEARTBEAT_INTERVAL_MS = parseInt(process.env.HEARTBEAT_INTERVAL_MS || '30000');
@@ -111,6 +111,7 @@ export interface TaskContext {
   workerId: string;
   task: WorkerTask;
   heartbeat: () => Promise<void>;
+  crawlRotator?: CrawlRotator;
 }
 
 export interface TaskResult {
@@ -134,7 +135,7 @@ const TASK_HANDLERS: Record<TaskRole, TaskHandler> = {
   store_discovery: handleStoreDiscovery,
   entry_point_discovery: handleEntryPointDiscovery,
   analytics_refresh: handleAnalyticsRefresh,
-  proxy_test: handleProxyTest,             // Tests proxy via ipify
+  whoami: handleWhoami,                     // Tests proxy + anti-detect
 };
 
 /**
@@ -555,6 +556,26 @@ export class TaskWorker {
 
       if (task) {
         console.log(`[TaskWorker] ${this.friendlyName} claimed task ${task.id} (${task.role}) [${this.activeTasks.size + 1}/${this.maxConcurrentTasks}]`);
+
+        // =================================================================
+        // PREFLIGHT CHECK - CRITICAL: Worker MUST pass before task execution
+        // Verifies: 1) Proxy available 2) Proxy connected 3) Anti-detect ready
+        // =================================================================
+        const preflight = await this.crawlRotator.preflight();
+        if (!preflight.passed) {
+          console.log(`[TaskWorker] ${this.friendlyName} PREFLIGHT FAILED for task ${task.id}: ${preflight.error}`);
+          console.log(`[TaskWorker] Releasing task ${task.id} back to pending - worker cannot proceed without proxy/anti-detect`);
+
+          // Release task back to pending so another worker can pick it up
+          await taskService.releaseTask(task.id);
+
+          // Wait before trying again - give proxies time to recover
+          await this.sleep(30000); // 30 second wait on preflight failure
+          return;
+        }
+
+        console.log(`[TaskWorker] ${this.friendlyName} preflight PASSED for task ${task.id} (proxy: ${preflight.proxyIp}, ${preflight.responseTimeMs}ms)`);
+
         this.activeTasks.set(task.id, task);
 
         // Start task in background (don't await)
@@ -611,6 +632,7 @@ export class TaskWorker {
         heartbeat: async () => {
           await taskService.heartbeat(task.id);
         },
+        crawlRotator: this.crawlRotator,
       };
 
       // Execute the task