Pin logger output in corpus diagnostic-divergence expectations

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### Description of the task

Extend the rolling-versus-exact parser corpus harness so every classified shared-rejection diagnostic divergence also pins caller-visible logger output for both parsers.

Acceptance criteria:

* `CorpusDiagnosticDivergence` records rolling and exact `LoggerExpectation` values.
* Corpus validation checks primary-buffer messages and warnings with `logger_expectation_mismatches` and reports side-specific drift.
* Focused regression coverage proves that changing either parser's primary buffer or warning list fails classification.
* Existing intentional diagnostic divergences remain explicitly classified without expanding production parser behavior.

### Additional context

Follow-up from #1097 and the unresolved review discussion about logger expectations in the corpus-wide diagnostic-only path.

Start with CorpusDiagnosticDivergence, LoggerExpectation, and logger_expectation_mismatches in the corpus validation harness, then review follow-up #1097 and the unresolved logger-expectation discussion. Trace how shared-rejection classifications are validated and add focused regression coverage showing that either parser's primary buffer or warning list causes classification to fail; existing intentional divergences should remain explicitly classified.

Written by the indexing model from the issue text.