frank-primary: prefix caching back ON — the OFF experiment did not fix the corruption

Frank: still corrupted at ~40k with --no-enable-prefix-caching deployed
and mechanically verified (zero gdn_hip faults in the container serving
that window, coherent 40,771-token boundary probe). The recurrence is
FAULT-FREE, so the align-mode page re-seed is not the (only) mechanism
and the mitigation bought whole-history re-prefill per turn for nothing.

Revert: knob FRANK_PRIMARY_NO_PREFIX_CACHING commented out -> the serve
branch renders --enable-prefix-caching (the shipped contract). The knob,
the branch and the seam stay documented for a future fixed fork build.

Open hypotheses recorded in the runbook: re-fed poisoned transcript (the
same conversation cannot distinguish fixed from unfixed), or a second
fault-free long-context path — fp8 KV at depth is the next suspect. Next
diagnostic: fresh-conversation reproduction, then a KV-dtype A/B.

scripts/frank-primary.env

@@ -175,7 +175,8 @@ FRANK_PRIMARY_KV_DTYPE=fp8
 FRANK_PRIMARY_MNBT=2048
 FRANK_PRIMARY_GATHER_CHUNKS=32
 FRANK_PRIMARY_GATHER_LANES=64
-# PREFIX CACHING IS OFF — THE FORK'S OWN NAMED MITIGATION (2026-10-05).
+# PREFIX CACHING: ON. An OFF experiment ran 2026-10-05 (below) and FAILED
+# to stop the corruption, so the historical flag is back.
 # MEASURED 2026-10-04, 18:46:07 PDT (5.6 h into the live boot, one running
 # request, prefix hit rate 48.1%): 48 gdn_hip state faults in one 0.6 s
 # burst, then the process-lifetime silence cap:
@@ -212,10 +213,19 @@ FRANK_PRIMARY_GATHER_LANES=64
 # history instead of at most 3135 tail tokens (a full 40k context costs
 # tens of seconds of TTFT per turn at this shape's prefill rate). A silently
 # corrupted conversation is worse than a slower first token.
-# RE-ENABLE PATH: if the fork ships a fixed align path, set this to empty,
-# redeploy, and re-verify by taking one conversation past 40,768 tokens
-# (decode must stay coherent and podman logs must show zero gdn_hip lines).
-FRANK_PRIMARY_NO_PREFIX_CACHING=1
+# RESULT (2026-10-05, later that day): THE MITIGATION DID NOT WORK. With
+# --no-enable-prefix-caching deployed and mechanically verified (zero
+# gdn_hip faults, a 40,771-token single-request boundary probe coherent),
+# live long conversations STILL degraded at ~40k on the running endpoint
+# (Frank, direct). The container serving that window logged ZERO faults
+# while the corruption reproduced, so the align-mode page re-seed is not
+# the (only) mechanism — see the runbook's RESULT note for the open
+# hypotheses (re-fed poisoned transcript vs a fault-free long-context
+# path such as fp8 KV at depth). Cost bought nothing: caching is back ON.
+# The knob stays commented for a future fork build with a fixed GDN state
+# path: set 1, redeploy, re-verify past 40,768 tokens (one conversation
+# coherent AND zero gdn_hip lines).
+# FRANK_PRIMARY_NO_PREFIX_CACHING=1
 # UTIL is an ARENA lever: the fork plans `budget = device_total x util`, and at
 # 31.86 GiB/card every +0.01 is +0.32 GiB of expert cache (~+139 slots), and
 # 0.982 is Frank's standing law: NEVER 1.00. The 1.00 attempt (2026-10-03,