Count invalid server-generated upload IDs

[nicolaslopezbravo]

Summary

Add FrontendRestRequestService.GeneratedBlobIdError to count InvalidBlobId failures while consuming server-generated upload IDs, including ID conversion and permanent-blob finalization.

Track generated-ID processing stages so invalid client-supplied IDs, including stitch chunk IDs, are excluded from the counter.

HTTP status codes, SLO accounting, callback exceptions, storage writes, cleanup, and retry behavior remain unchanged.

Excluding client-supplied IDs

BLOB_ID_IS_SERVER_GENERATED is set only after a successful router upload/stitch result. Client-supplied stitch chunk IDs are validated before that point; failures propagate without setting the marker.

The counter increments only when both the marker is true and the error is RouterErrorCode.InvalidBlobId. The marker is cleared after successful generated-ID processing, before subsequent response handling.

Tests inject failures at router, ID-conversion, and TTL-finalization stages, verifying zero increments for router-stage input failures and one increment for qualifying generated-ID failures. These tests verify the callback boundary; they do not exercise malformed chunk IDs through the real stitch parser.

Testing Done

Validated on JDK 11:

• 30 frontend tests and 2 router parameterizations passed.
• 6 existing frontend-config tests passed.
• Applied the complete patch to v0.5.194 and passed 4 focused frontend tests, 2 router parameterizations, and 6 config tests.

Coverage includes exactly-once metric increments, exclusion of client-supplied invalid IDs and unrelated failures, unchanged HTTP classification and exception causes, successful-path marker cleanup, and asynchronous ID conversion.

Copilot assisted with implementation and tests.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 70.83333% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 50.75%. Comparing base (52ba813) to head (cdd5d33).
⚠️ Report is 423 commits behind head on master.

Files with missing lines	Patch %	Lines
...hub/ambry/frontend/FrontendRestRequestService.java	40.00%	2 Missing and 1 partial ⚠️
...com/github/ambry/frontend/NamedBlobPutHandler.java	50.00%	3 Missing ⚠️
...ava/com/github/ambry/router/NonBlockingRouter.java	0.00%	1 Missing ⚠️

Additional details and impacted files

@@              Coverage Diff              @@
##             master    #3304       +/-   ##
=============================================
- Coverage     64.24%   50.75%   -13.50%     
+ Complexity    10398     8713     -1685     
=============================================
  Files           840      939       +99     
  Lines         71755    80824     +9069     
  Branches       8611     9752     +1141     
=============================================
- Hits          46099    41022     -5077     
- Misses        23004    36399    +13395     
- Partials       2652     3403      +751     

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