Avoid unnecessary model reviews and speculative type repairs

[SamG-Coder]

Candidates that cannot pass the local single-function body check were still sent to the model reviewer, wasting a review call before repair. The prompts also required named members without type evidence, encouraging helper structs that conflict with the accepted candidate format.

This change checks candidate shape before model review and sends failures directly through the existing repair/checkpoint path. The log records skipped reviews. Reconstruction and review prompts now allow evidence-preserving byte offsets when layouts are unknown and request exactly one function definition.

Validation:

• 196 tests passed, 9 platform-dependent skips.
• Ruff passed; Mypy passed with the Linux platform target.
• Regression tests cover malformed bodies, helper definitions, multiple functions, bounded repair, and repeated failures without reviewer calls.
• Offline replay of a local workload identified 24 of 128 completed reviews that the preflight would have avoided. This measures avoidable reviews, not an end-to-end speedup.

Follow-up to #12. Contains two separate fixes with tests; no binaries, generated source, or run reports are included.