bottleneck_dim=16 causes w_s1 size mismatch between VarStore (full state_dim)
and flat params_buf (reduced bottleneck_concat_dim). EMA target sync crashes
with CUDA_ERROR_ILLEGAL_ADDRESS.
Root cause: GpuVarStore allocates weights at full state_dim but GpuDqnTrainer's
flat buffer uses bottleneck-reduced dimensions. These two weight sources are
fundamentally incompatible when bottleneck is active.
Fix: eliminate GpuVarStore entirely (next task), then re-enable bottleneck.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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