[grade=B] DC-093: Workflow engine retry with exponential backoff

Actions now retry up to 3 times with 2/4/8s exponential backoff before
giving up. Logs each retry attempt with attempt count. exhaustedRetries
field in failure result shows total attempts made.

All 1540 tests pass.

dashcaddy-api/src/recipes/bundled-workflows.js

@@ -252,32 +252,49 @@ class WorkflowEngine extends EventEmitter {
    */
   async _runActions(actions, triggerData = {}) {
     const results = [];
+    const MAX_RETRIES = 3;
+    const RETRY_DELAY_MS = 2000;
 
     for (let i = 0; i < actions.length; i++) {
       const action = actions[i];
       const previousResult = i > 0 ? results[i - 1] : null;
-      // notify-on-failure needs to see the previous action's outcome to decide
-      // whether to fire. Passing the full results array in the trigger data lets
-      // executeAction do that lookup without changing the action shape.
-      // Also surface failingServices (set by healthCheckService on throw) so
-      // template variables like {{failingServices}} can interpolate.
       const actionContext = {
         ...triggerData,
         previousResult,
         failingServices: previousResult && previousResult.failingServices ? previousResult.failingServices : undefined,
       };
+
+      // DC-093: Retry with exponential backoff for transient failures
+      let lastError = null;
+      let result = null;
+      let succeeded = false;
+
+      for (let attempt = 0; attempt <= MAX_RETRIES; attempt++) {
         try {
-        const result = await this.executeAction(action, actionContext);
-        results.push({ action: action.type, success: true, result });
+          result = await this.executeAction(action, actionContext);
+          succeeded = true;
+          break;
         } catch (error) {
-        log.error('workflow', error, { actionType: action.type });
+          lastError = error;
+          if (attempt < MAX_RETRIES) {
+            const delay = RETRY_DELAY_MS * Math.pow(2, attempt);
+            log.warn('workflow', `Action "${action.type}" failed (attempt ${attempt + 1}/${MAX_RETRIES + 1}), retrying in ${delay}ms`, { error: error.message });
+            await new Promise(resolve => setTimeout(resolve, delay));
+          }
+        }
+      }
+
+      if (succeeded) {
+        results.push({ action: action.type, success: true, result });
+      } else {
+        log.error('workflow', `Action "${action.type}" failed after ${MAX_RETRIES + 1} attempts`, { error: lastError.message });
         results.push({
           action: action.type,
           success: false,
-          error: error.message,
-          failingServices: error.failingServices,
+          error: lastError.message,
+          failingServices: lastError.failingServices,
+          exhaustedRetries: MAX_RETRIES + 1,
         });
-        // Continue with other actions but log failure
       }
     }