test(metering): find the actor key in any meterIncr argument

The buffered write now passes the claim key too, which moves the counter
key's position. The image provider's write-ordering test matched it by
index and stopped seeing the write.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/backend/drivers/ai-image/providers/openai/OpenAiImageProvider.test.ts

@@ -253,7 +253,8 @@ describe('OpenAiImageProvider.generate credit gate', () => {
         });
         let blocked = false;
         vi.spyOn(redis, 'meterIncr').mockImplementation(async (...args) => {
-            if (!blocked && args[5].includes(`:actor:${actor.user!.uuid}:`)) {
+            const actorKey = `:actor:${actor.user!.uuid}:`;
+            if (!blocked && args.some((arg) => arg.includes(actorKey))) {
                 blocked = true;
                 await held;
             }