frank-primary: prefix caching OFF — the fork's QFN align-mode GDN state fault

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.

scripts/serve-frank-primary.sh

@@ -25,7 +25,9 @@
 # --max-num-batched-tokens 2048 (Frank's call 2026-10-03; arena-free because the
 # registry prices overhead flat up to its nbt 4096 anchor), MoE gather geometry
 # R4D_LRU_GATHER_CHUNKS=32 / R4D_LRU_GATHER_LANES=64 (+18.7% decode, grows
-# with depth), prefix caching, expert prefetch OFF (36% precision measured),
+# with depth), prefix caching OFF 2026-10-05 (the fork's QFN align-mode GDN
+# state fault — the evidence block is in frank-primary.env), expert prefetch
+# OFF (36% precision measured),
 # TunableOp off. Shape E adds --expert-precise-memory (fitted 5.25 GiB overhead
 # instead of the 7.60 GiB default -> expert arena 17.22 GiB / 7,522 slots, +16%)
 # and GPU_MAX_HW_QUEUES=2; shape F pins the plan's CUDA-graph term to the
@@ -160,7 +162,12 @@ podman run -d --name "$FRANK_PRIMARY_CONTAINER" \
   --gpu-memory-utilization "$FRANK_PRIMARY_UTIL" \
   --kv-cache-memory-bytes "$FRANK_PRIMARY_KV_BYTES" \
   --kv-cache-dtype "$FRANK_PRIMARY_KV_DTYPE" \
-  --enable-prefix-caching \
+  # Prefix caching: the fork's QFN mamba align path corrupts GDN SSM state at
+  # ~40k tokens (2026-10-04, 48 gdn_hip state faults, one request). FRANK_
+  # PRIMARY_NO_PREFIX_CACHING flips to the fork-named mitigation
+  # (--no-enable-prefix-caching); empty keeps the historical flag. The
+  # evidence block is in frank-primary.env.
+  ${FRANK_PRIMARY_NO_PREFIX_CACHING:+--no-enable-prefix-caching}${FRANK_PRIMARY_NO_PREFIX_CACHING:---enable-prefix-caching} \
   --enable-auto-tool-choice --tool-call-parser "$FRANK_PRIMARY_TOOL_PARSER" \
   --reasoning-parser "$FRANK_PRIMARY_REASONING_PARSER" \
   --default-chat-template-kwargs "$FRANK_PRIMARY_CHAT_TEMPLATE_KWARGS" \