Decision
Scheduler chunks must not become model boundaries.
Qwen4Exp’s PLE path combines token-history-derived row selection with a dilated causal convolution. Both operations depend on preceding tokens. A runtime is free to divide prefill into ubatches for memory or scheduling reasons, but that division is not visible to the model.
Hebrus therefore owns PLE history and convolution tails per logical sequence and carries them across every ubatch. The state advances in token order, including the frozen current-EOS rule, regardless of how the caller partitions the same input.
The hidden receptive field
A causal convolution with kernel width four and dilation three needs nine preceding positions of state. Keeping only the last contiguous three values would look plausible and still be wrong: the next output reads spaced historical positions.
The correct persistent state is derived from the receptive field, not from the number of coefficients or the current ubatch size.
The history hash has a similar trap. Resetting at a chunk boundary changes bigram and trigram row identities even though the user supplied one continuous sequence.
Evidence shape
Phase 5 compares the same token sequence executed in one shot and in a 1/2/1-token partition. It checks more than final logits:
- the generated PLE row identities;
- persistent convolution bytes;
- the digest of all public state owners;
- final output;
- behavior at the EOS transition;
- isolation between independent sequence state images.
Comparing only the last output could allow offsetting state defects to escape.
Ownership rule
Persistent sequence state should be addressed by a stable slot plus generation, not by the temporary row number of the current ubatch. Copy, rewind, reset, and future cache reuse must operate on the history and convolution group together.
This is also why the state belongs inside the whole-chunk transaction described in AFN-010. A failed later stage must not leave PLE one token ahead of the public frontier.
Agent checklist
For any chunked stateful operator:
- derive the exact historical receptive field;
- separate logical sequence ownership from batch placement;
- specify update order around EOS and reset events;
- compare internal state as well as output across partitions;
- include a multi-sequence isolation case;
- make failure preserve the pre-chunk snapshot.
Failure boundary
These tests use tiny resident rows and deterministic F32 computation. Production PLE storage, decoding, page leases, cancellation, cold/warm behavior, and SSD overlap remain Phase 7 work.