feat: add MCP corruption corpus coverage artifact

[ProfRandom92]

Motivation

• Add a deterministic, artifact-backed summary that proves the materialized MCP corruption corpus is fully native-covered (18/18) and reproducible from committed fixtures, manifest, contracts, and ContractValidator.
• Keep the project artifact-first, deterministic, narrowly-scoped, and audit-oriented without adding runtime orchestration, LLM judging, or external dependencies.

Description

• Add scripts/generate_mcp_corruption_coverage_artifact.py which loads artifacts/mcp_trace_corruption_manifest.json, source originals, materialized corruptions, and original contracts, then runs ContractValidator to compute observed failure labels and per-entry native coverage and evidence, failing on missing files, unregistered labels, malformed entries, or adapter gaps.
• Commit the deterministic artifact artifacts/mcp_corruption_coverage.json (sorted keys, indent=2, no timestamps, repository-relative paths) that contains top-level metadata, coverage summary, operator/family/label distributions, and per-entry deterministic evidence.
• Add tests tests/test_mcp_corruption_coverage_artifact.py that assert committed artifact equals regenerated output, generation stability, exact summary/distribution counts, per-entry coverage invariants, taxonomy registration, no absolute paths/timestamps, and generator failure on missing expected labels.
• Enforce strict invariants only (no new validation semantics or failure labels), and keep the implementation standard-library-only, simple, and auditable.

Testing

• Changed files: scripts/generate_mcp_corruption_coverage_artifact.py, artifacts/mcp_corruption_coverage.json, tests/test_mcp_corruption_coverage_artifact.py.
• Ran python scripts/generate_mcp_corruption_coverage_artifact.py which completed and wrote artifacts/mcp_corruption_coverage.json (pass).
• Ran pytest -q tests/test_mcp_corruption_coverage_artifact.py (6 passed).
• Ran pytest -q tests/test_mcp_trace_corruption_validation.py (6 passed), pytest -q tests/test_mcp_trace_corruption_manifest.py tests/test_mcp_trace_corruption_materialization.py (combined pass), and pytest -q tests/test_contract_validator.py (19 passed).
• Ran full repository check npm run check which executed the python and dashboard checks and pytest suite and completed successfully (321 passed).

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Codex Task

[gemini-code-assist]

Code Review

This pull request introduces a system for generating and verifying MCP corruption coverage artifacts, including a generation script, the resulting coverage JSON, and a comprehensive test suite. The reviewer provided feedback to improve the robustness of JSON parsing by handling null values and validating item types, suggested removing redundant sorting logic in evidence key collection, and recommended using idiomatic pytest fixtures for mocking instead of subprocess calls.