fix(inference): correct Piscina queue-saturation message match in PiiRegexWorkerService

Address review feedback: the service matched 'Task queue is at capacity' but
Piscina 5.3.1 throws 'Task queue is at limit', so the saturation branch never
fired. Fixed the string in the service and the mock in the test. Piscina does
not expose a stable error code, so message matching is the only option;
added a comment pinning the verified version.

Reviewed-at: elastic#288758 (comment)

Author: jonwalstedt

x-pack/platform/plugins/shared/inference/server/workflow_anonymization/detection/regex_worker_service.test.ts

@@ -126,7 +126,7 @@ describe('PiiRegexWorkerService', () => {
       service = new PiiRegexWorkerService(createTestConfig(), logger);
       jest
         .spyOn((service as any).worker, 'run')
-        .mockRejectedValueOnce(new Error('Task queue is at capacity'));
+        .mockRejectedValueOnce(new Error('Task queue is at limit'));
 
       await expect(service.run(IP_PAYLOAD)).rejects.toThrow('queue at capacity');
     });
@@ -135,7 +135,7 @@ describe('PiiRegexWorkerService', () => {
       service = new PiiRegexWorkerService(createTestConfig(), logger);
       jest
         .spyOn((service as any).worker, 'run')
-        .mockRejectedValueOnce(new Error('Task queue is at capacity'));
+        .mockRejectedValueOnce(new Error('Task queue is at limit'));
 
       const results = await service.run(IP_PAYLOAD, 'allow_unsafe');
 

x-pack/platform/plugins/shared/inference/server/workflow_anonymization/detection/regex_worker_service.ts

@@ -88,7 +88,9 @@ export class PiiRegexWorkerService {
             `PII regex detection task timed out after ${this.config.taskTimeout.asMilliseconds()}ms`
           );
         }
-        if (err instanceof Error && err.message === 'Task queue is at capacity') {
+        // Piscina does not expose a stable error code; match on the message
+        // (verified against piscina@5.3.1 dist/errors.js TaskQueueAtLimit).
+        if (err instanceof Error && err.message === 'Task queue is at limit') {
           throw new Error(
             `PII regex detection rejected: worker queue at capacity (maxQueue=${this.config.maxQueue})`
           );