Two root causes of cross-process non-determinism fixed:
1. MSE→C51 graph switch: graph_forward_mse and graph_forward were
captured in different sessions with different cublasLtMatmul configs.
Fix: always use blended graph_forward (c51_alpha controls blend).
Deleted LossMode enum, graph_forward_mse, and all switching code.
2. Multiple capture sessions at steps 0-2: graph_forward, graph_ddqn,
and graph_adam were captured individually before graph_mega at step 2.
Each capture contaminated cuBLAS internal state.
Fix: capture graph_mega at step 0 (single capture session).
Result: runs with same initial cublasLtMatmul capture are fully
bit-identical across all 30 epochs. Remaining cross-process variation
is from the single initial cublasLtMatmul call during graph capture.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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