fix: redact metadata secret previews

[mldangelo-oai]

Summary

• redact metadata secret match_preview evidence before results are serialized
• preserve useful context for Bearer and assignment-shaped matches while fully redacting standalone token formats
• add regression coverage for AWS, OpenAI, GitHub, Bearer, and API-key assignment previews

Validation

• PYTHONPATH=/private/tmp/modelaudit-c115 PROMPTFOO_DISABLE_TELEMETRY=1 /Users/mdangelo/code/modelaudit/.venv/bin/pytest tests/scanners/test_metadata_scanner.py -q
• /Users/mdangelo/code/modelaudit/.venv/bin/ruff format --check modelaudit/scanners/metadata_scanner.py tests/scanners/test_metadata_scanner.py
• /Users/mdangelo/code/modelaudit/.venv/bin/ruff check modelaudit/scanners/metadata_scanner.py tests/scanners/test_metadata_scanner.py
• PYTHONPATH=/private/tmp/modelaudit-c115 /Users/mdangelo/code/modelaudit/.venv/bin/mypy modelaudit/scanners/metadata_scanner.py tests/scanners/test_metadata_scanner.py
• git diff --check

[mldangelo-oai]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. 🚀

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[github-actions]

Workflow run and artifacts

Performance Benchmarks

Compared 12 shared benchmarks with a regression threshold of 15%.
Status: 0 regressions, 0 improved, 12 stable, 0 new, 0 missing.
Aggregate shared-benchmark median: 577.24ms -> 578.07ms (+0.1%).

Workload	Benchmark	Target	Size	Files	Baseline	Current	Change	Status
chunked-upload-stream	tests/benchmarks/test_picklescan_benchmarks.py::test_picklescan_chunked_upload_stream	chunked_stream	278.2 KiB	1	15.68ms	16.37ms	+4.4%	stable
nested-payload-review	tests/benchmarks/test_picklescan_benchmarks.py::test_picklescan_nested_payload_review[nested_base64]	nested_base64	98 B	1	326.1us	317.6us	-2.6%	stable
nested-payload-review	tests/benchmarks/test_picklescan_benchmarks.py::test_picklescan_nested_payload_review[nested_raw]	nested_raw	78 B	1	320.1us	314.7us	-1.7%	stable
warm-cache-rescan	tests/benchmarks/test_scan_benchmarks.py::test_scan_warm_cached_repository_rescan	release-candidate	547.3 KiB	32	50.75ms	50.33ms	-0.8%	stable
mixed-model-repository	tests/benchmarks/test_scan_benchmarks.py::test_scan_release_candidate_repository	release-candidate	547.3 KiB	32	222.62ms	224.37ms	+0.8%	stable
nested-payload-review	tests/benchmarks/test_picklescan_benchmarks.py::test_picklescan_nested_payload_review[nested_hex]	nested_hex	130 B	1	324.8us	326.9us	+0.6%	stable
padded-multi-stream-upload	tests/benchmarks/test_picklescan_benchmarks.py::test_picklescan_padded_multi_stream_upload	multi_stream_padded	4.1 KiB	1	1.18ms	1.19ms	+0.6%	stable
duplicate-heavy-registry	tests/benchmarks/test_scan_benchmarks.py::test_scan_duplicate_registry_snapshot	registry-snapshot	915.2 KiB	13	164.56ms	163.65ms	-0.6%	stable
suspicious-pickle-intake	tests/benchmarks/test_scan_benchmarks.py::test_scan_suspicious_pickle_intake	suspicious-intake	183.8 KiB	4	76.33ms	76.12ms	-0.3%	stable
single-checkpoint-preflight	tests/benchmarks/test_scan_benchmarks.py::test_scan_single_checkpoint_before_load	single_checkpoint.pkl	183.0 KiB	1	30.62ms	30.55ms	-0.2%	stable
direct-malicious-upload	tests/benchmarks/test_picklescan_benchmarks.py::test_picklescan_direct_malicious_upload	malicious_reduce	52 B	1	1.13ms	1.14ms	+0.2%	stable
clean-training-checkpoint	tests/benchmarks/test_picklescan_benchmarks.py::test_picklescan_clean_training_checkpoint	safe_large	278.2 KiB	1	13.40ms	13.41ms	+0.1%	stable

[ianw-oai]

Looks good.