Pre-e2e audit fixes for NSA index-topk sharing (index_topk_pattern):
- Validate the pattern at init: F/S charset only, must start with F
(layer 0 has nothing to share from), and length must equal
num_hidden_layers — a short pattern previously crashed deep in pool
init with an obscure per-layer ValueError, a long one silently
ignored tail characters. Warn when a pattern shadows a configured
index_topk_freq (pattern takes precedence silently otherwise).
- Fail fast when a shared (S) layer receives prev_topk_indices=None:
both gated indexer call sites previously fell through to omitting
topk_indices entirely, running sparse attention without indices and
silently corrupting output if threading were ever dropped.
- Reject pipeline parallelism with index-topk sharing (same rationale
as the existing TBO guard): topk indices are not threaded across
PP-stage boundaries, and each stage's loop resets them to None.
- Gate the CP shared-KV index prefetcher on the next layer having an
index-cache slot: prefetching an S layer's nonexistent buffer
tripped the inactive-layer fail-fast and disabled the prefetcher
for the entire run on the first F->S transition.
- Log the resolved active index layer plan at pool init so an e2e run
can confirm IndexCache is actually on.
Tests: pattern validation cases incl. the GLM-5 reference 78-char
pattern, next_skip == skip-of-next invariant; existing 'C' pattern
test updated to upstream 'F' charset.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
leavelet
3eef989739