Measured 2026-10-04 18:46:07 PDT (live podman logs): 48 gdn_hip state
faults in one 0.6 s burst — 'state out of ssm-cache range: max|S|=0 with
non-finite values (slot=42 head=3|8)', one per TP rank, 23 GDN layers
each — then the process-lifetime report cap. The guard's own text in
this build names it: 'known Qwen3.8-Flash-Next (QFN) flaw under prefix
caching … Mitigation: --no-enable-prefix-caching'.
Mechanism: prefix caching puts QFN on mamba_cache_mode 'align', which
checkpoints each sequence's GDN recurrent state into a mamba page per
3136-token block and re-seeds it from that page when a request resumes
from a cached prefix. The NaN state landed at the 13th boundary
(13 x 3136 = 40,768 — the reported ~40k mark) and persisted in the page:
every later turn of that conversation re-seeded the same non-finite
state for two heads, silently (fault-report cap already spent).
RAM ruled out the same day: zero MCE/EDAC records since the boot under
test, 8 GiB in-band pattern stable under live load, 4800 MT/s is the
JEDEC floor on 5600-rated DIMMs, and the two-head single-slot NaN
signature is a state-path fault, not scattered bit corruption.
Fix: FRANK_PRIMARY_NO_PREFIX_CACHING=1 -> --no-enable-prefix-caching
(flag renders in both directions from the knob). Cost: every turn
re-prefills the whole history instead of at most 3135 tail tokens.
Seam updated: the prefix-cache pin now asserts the conditional render
and the shipped OFF value. Runbook carries the evidence + acceptance
criteria; all 368 tests pass.
Frank
9d8b18553d