Asserts that a pre-MoE checkpoint (old architecture hash) is rejected
with a clear architecture-mismatch error. Confirms the no-fallback
contract per spec §6.4 — old checkpoints fail loudly, no silent
loading of incompatible weights.
Four cases: zeroed-out hash rejected, missing metadata rejected,
missing arch_hash field rejected, and matching metadata accepted.
All tests are pure CPU with no CUDA or file I/O.
Spec: docs/superpowers/specs/2026-04-27-moe-regime-redesign-design.md §8.5.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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