fix: use useFactory returning array + Array.isArray guard for RESULT_PROJECTORS

Two changes to fix 'projectors is not iterable' TypeError:

1. ai-job.module.ts: Replace useClass+multi:true with useFactory that
   explicitly returns [p] — avoids NestJS multi-provider array-wrapping
   ambiguity. SyntheticResultProjector back as standalone provider.

2. projection-executor.service.ts: Replace truthiness check with
   Array.isArray() guard for defense-in-depth.

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

src/modules/ai-job/ai-job.module.ts

@@ -30,7 +30,8 @@ import { SyntheticRegistrationService } from './synthetic-registration.service';
     AiJobExecutionEngineImpl,
     ProjectionExecutor,
     SyntheticRegistrationService,
-    { provide: RESULT_PROJECTORS, useClass: SyntheticResultProjector, multi: true } as any,
+    SyntheticResultProjector,
+    { provide: RESULT_PROJECTORS, useFactory: (p: SyntheticResultProjector) => [p], inject: [SyntheticResultProjector] } as any,
     { provide: AI_JOB_EXECUTION_ENGINE, useExisting: AiJobExecutionEngineImpl },
   ],
   exports: [

src/modules/ai-job/projection-executor.service.ts

@@ -28,14 +28,13 @@ export class ProjectionExecutor {
     @Inject(RESULT_PROJECTORS)
     projectors?: ResultProjector[],
   ) {
-    if (projectors) {
-      for (const p of projectors) {
+    const projectorList = Array.isArray(projectors) ? projectors : [];
+    for (const p of projectorList) {
         if (this.projectorMap.has(p.key)) {
           this.logger.warn(`Duplicate projector key "${p.key}" — overwriting`);
         }
         this.projectorMap.set(p.key, p);
     }
-    }
     this.logger.log(
       `ProjectionExecutor initialized with ${this.projectorMap.size} projector(s): ` +
       `[${Array.from(this.projectorMap.keys()).join(', ') || 'none'}]`,