Add deterministic recipe parser fuzz gate

[dovvnloading]

Summary

• Add a deterministic, bounded parser-fuzz qualification probe for image, calculator, and check payloads.
• Assert stable redacted RecipeValidationError categories, canonical identity, reproducibility, and iteration budgets.
• Fix check.v1 optional tolerance validation so is_close with None fails closed as invalid_check instead of leaking an AttributeError.
• Add regression tests and update the Phase 2 ADR/qualification README with the evidence and remaining release gates.

Why this is needed

Parser fuzzing is an explicit Phase 2 release gate. The first 2,000-case run found a real edge-case defect in the tolerance: Decimal | None validator: a None value called the non-optional decimal validator and escaped as an uncaught AttributeError. The optional validator now preserves the typed contract and the regression test locks the stable failure category.

Validation

• Deterministic parser fuzz (--iterations 2000 --seed 20260728 --json --strict): 158 accepted, 1,842 rejected, 0 unexpected exceptions.
• Fuzz regression and recipe-contract tests: 19 passed.
• Full Python suite: 263 passed, 1 Windows-inapplicable skip, 1 existing pytest-asyncio deprecation warning.
• compileall and git diff --check passed.
• No production execution provider is enabled by this change.

Release-gate status

This closes deterministic parser-fuzz evidence. Artifact security review, resource/watchdog accounting, external review, and production lifecycle health/wiring remain explicit blockers before provider enablement.

Cortex.pyproj was intentionally excluded because it contains an unrelated user edit.

Builds on merged PR #53.