Switch alpha_window_push from circular-buffer-with-head_idx layout
to shift+insert layout matching production mamba2_update_history.
Slot 0 = oldest, slot K-1 = newest after each push, matching
Mamba2Block's [B, K, in_dim] input contract directly (no reorder).
Cost: O(K-1) shifts per state_dim feature per push. For K=16,
state_dim=10: 10 threads × ~15 ops each = trivial.
Kernel signature: drops head_idx, adds K. Test updated to verify
chronological shift across 3 pushes into 4-slot buffer.
docs/isv-slots.md updated per kernel-audit-doc hook.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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