docs(inference): update PiiDetectionFailureMode docstring for narrowed allow_unsafe semantics

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: jonwalstedt

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

@@ -54,6 +54,7 @@ export interface PiiRegexWorkerTaskPayload {
  *
  * `block` refuses to produce a partial result, so a broken rule fails the LLM call
  * rather than letting the PII class it was meant to catch through unmasked.
- * `allow_unsafe` logs the failure and returns no matches for the entire payload.
+ * `allow_unsafe` logs and skips each invalid rule; valid rules still run and return their matches.
+ * Infrastructure failures (timeout, queue saturation) still return no matches for the entire payload.
  */
 export type PiiDetectionFailureMode = 'block' | 'allow_unsafe';