frank-primary: revert to known-good fp8 3x262144

The 2 x 200704 fp8 / MNBT 1024 shape (30904ba) crash-loops at boot: the
engine dies in determine_available_memory -> profile_run -> _dummy_run with
the SAME torch.compile dynamo constraint that killed the bf16 2 x 262144
shape on 2026-10-01:

  RuntimeError: Worker failed with error 'Constraints violated
  (L['query_start_loc'].size()[0])! You marked it as dynamic but your code
  specialized it to be a constant (3)'

Not an OOM. Restoring the last shape measured serving (fp8 3 x 262144 /
KV 6.1e9 / MNBT 2048 / arena 6,248) so the endpoint serves again; the
desired edits are re-applied one at a time from this base.

scripts/serve-frank-primary.sh

@@ -11,16 +11,14 @@
 # every flag here was qualified by boot probe on 2026-09-29 — see
 # frank-primary.env for the qualification record).
 #
-# Shape (2026-10-02, Frank's correction of the 10-01 bf16 shape): MAXLEN
-# 200704 x SEQS 2 (401,408 tokens of contract), KV fp8 (--kv-cache-dtype
-# fp8; the bf16 unquantized shape is retired to git tag
-# frank-primary-fp8-mtp-20261001), KV_BYTES 3,150,000,000 PER RANK (the
-# engine measured 405,000 tokens of capacity / ~3.0x concurrency), NO
-# speculative decode, --max-num-batched-tokens 1024 (Frank's lock), 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), TunableOp off, and
-# the pool deliberately small so the expert arena keeps what it reclaims.
+# Shape (2026-10-01 bf16 cutover): MAXLEN 262144 x 3 sessions (786,432
+# tokens), KV UNQUANTIZED (--kv-cache-dtype auto = bf16; the fp8 q8/q8 shape
+# is retired to git tag frank-primary-fp8-mtp-20261001), KV_BYTES
+# 11,047,010,304 PER RANK (the engine measured 798,280 tokens of capacity /
+# 3.05x concurrency), NO speculative decode, --max-num-batched-tokens 1024
+# (Frank's lock), 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), TunableOp off.
 #
 # The root unit (scripts/frank-primary.service, User=dank,
 # LimitMEMLOCK=infinity) grants the pin budget for the tiered-expert host