Wire the gradient vaccine's validation batch through the training loop:
- Pre-sample a SECOND batch from PER alongside each training batch
- Pass via FusedTrainingCtx::pending_vaccine_batch (consumed per step)
- Separate PER indices ensure train and val batches are independent
The vaccine's non-graph forward+backward runs on this held-out batch
to produce g_val. Gradient projection (dot + SAXPY) ensures g_train
only moves in directions where both batches agree.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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