CfcTrunk owns weights, ping-pong hidden buffers, and pre-allocated
per-step scratch (snap features, probs, projection output). Modules
and CudaFunction handles cached at new_random so the hot path
avoids reload. forward_snapshot dispatches snap_feature_assemble ->
cfc_step -> heads -> projection sequentially; Graph A capture (Task 11)
will fold these into a single launch.
The Mamba2 prefix (per 2026-05-16 spec amendment) is added in a
follow-up task before Graph A capture.
Tests (5/5 on sm_86):
- probs in [0,1] across all 5 horizons
- hidden state changes after forward
- probs + proj are finite
- layer-norm proj has near-zero mean
- 50-step run leaves hidden finite
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
