frank-primary: 3 slots x 200704, fp8, pool sized for 2 contexts

Re-applies the desired shape incrementally on the proven-good fp8 3x262144
base, after bisecting why the first attempt (30904ba) crash-looped.

Root cause: `--max-num-seqs 2` cannot compile on this model. AOT
build_guards(strict_error=True) inside profile_run -> _dummy_run specializes
`query_start_loc`'s width to SEQS + 1 (3 at SEQS 2, 4 at SEQS 3) and the
ConstraintViolationError kills engine init ~7 min in. MNBT is orthogonal:
SEQS 2 failed at MNBT 1024 AND 2048; SEQS 3 passed at both. KV dtype was a
red herring. Measured by four single-variable boot probes.

Arena lever measured: the expert arena is sized from `max_model_len` via the
registry-priced KV reserve (9190 B/token x max_model_len), NOT from
--kv-cache-memory-bytes. 262144 -> 14.30 GiB / 6,248 slots; 200704 ->
14.87 GiB / 6,496 slots. The 6.1e9 -> 3.15e9 pool cut bought zero arena and
is a runtime-headroom lever.

Shape: MAXLEN 200704, SEQS 3 (unchanged - the only slot count that compiles),
KV_BYTES 3.15e9/rank = 2.04x full-length concurrency at 7,701 B/token fp8,
MNBT 1024, gather 32x64, no spec decode, no prefetch, no precise-memory.

tests/frank_primary_unit.bats

@@ -90,28 +90,35 @@ DOWNLOAD="$REPO_ROOT/scripts/download-frank-primary.sh"
 }
 
 @test "the qualified engine shape is in the env file" {
-    # 2026-10-01 night ladder (Frank's method), then a runtime-survivability
-    # correction. SEQS=3 bf16 topped out at 241664 (KV 732,359 / 3.03x);
-    # SEQS=6 fp8 does NOT fit (6 x 241664 asked 10.70 GiB against 9.18 GiB
-    # free); SEQS=5 fp8 x 262144 BOOTED (KV 1,350,182 / 5.15x) but left ~0
-    # bytes free at runtime and a real client request (995-token prompt with
-    # max_tokens=261149) killed the worker with `Tried to allocate 50.00 MiB
-    # ... 0 bytes free`. FOUR slots at the full native 262144 window is the
-    # deployed shape: ~1.93 GiB more headroom per rank for
-    # activations/graphs. UTIL stays 0.98 (lowering it shrinks the engine's
-    # own budget instead of buying slack).
-    # FINAL (2026-10-01, Frank): TWO full-size windows with BF16 KV plus
-    # --expert-precise-memory. bf16 costs 13,839 B/token (measured), so
-    # 2 x 262144 = 524,288 tokens needs 7.256e9 B; pinned at 7.3e9 (~527.5k
-    # tokens, 3,206 margin). The precise flag drops the plan's overhead
-    # 7.60 -> 5.25 GiB, moving the arena from 6,248 to ~7,278 slots.
-    grep -q '^FRANK_PRIMARY_MAXLEN=262144$' "$ENV_FILE"
+    # 2026-10-02 shape D. History: the 2026-10-01 night ladder put SEQS=3
+    # bf16 at 241664 (KV 732,359 / 3.03x); SEQS=6 fp8 does NOT fit (6 x
+    # 241664 asked 10.70 GiB against 9.18 GiB free); SEQS=5 fp8 x 262144
+    # BOOTED (1,350,182 / 5.15x) but left ~0 bytes free and a real 995-token
+    # request killed the worker with `Tried to allocate 50.00 MiB ... 0 bytes
+    # free`. UTIL stays 0.98 (lowering it shrinks the engine's own budget
+    # instead of buying slack).
+    # SEQS=2 is IMPOSSIBLE on this model, measured 2026-10-02 by
+    # single-variable boot probe against the then-deployed shape: SEQS 2 fails
+    # at BOTH MNBT 1024 and 2048 with torch.fx ConstraintViolationError
+    # (query_start_loc.size()[0] marked dynamic but specialized to a constant
+    # (3)); SEQS 3 passes at both. model_runner sizes that buffer
+    # max_num_reqs + 1, so the width is SEQS + 1 and MNBT only moves the
+    # compile RANGE.
+    # So the shape is 3 slots with a pool that admits only ~2 full-length
+    # conversations: fp8 measures 7,701 B/token, one 200704 request costs
+    # 1.546e9 B, and KV_BYTES 3.15e9 therefore gives 2.04x. Shorter requests
+    # use the spare blocks; a third LONG request queues.
+    # The arena is sized by max_model_len, NOT by KV_BYTES: the planner
+    # reserves registry 9190 B/token x max_model_len (2.48 GiB at 262144 ->
+    # arena 6,248 slots; 1.91 GiB at 200704 -> 6,496). The pool cut buys
+    # runtime headroom, not arena.
+    grep -q '^FRANK_PRIMARY_MAXLEN=200704$' "$ENV_FILE"
     grep -q '^FRANK_PRIMARY_SEQS=3$' "$ENV_FILE"
     grep -q '^FRANK_PRIMARY_UTIL=0.98$' "$ENV_FILE"
-    grep -q '^FRANK_PRIMARY_KV_BYTES=6100000000$' "$ENV_FILE"
-    grep -q '^FRANK_PRIMARY_MNBT=2048$' "$ENV_FILE"
+    grep -q '^FRANK_PRIMARY_KV_BYTES=3150000000$' "$ENV_FILE"
+    grep -q '^FRANK_PRIMARY_MNBT=1024$' "$ENV_FILE"
     grep -q '^FRANK_PRIMARY_KV_DTYPE=fp8$' "$ENV_FILE"
-    # --expert-precise-memory is NOT set: with bf16 2 x 262144 it put the boot
+    # --expert-precise-memory is NOT set: it put the bf16 2 x 262144 boot
     # 0.13 GiB from the 31.86 GiB ceiling (arena 16.65 device-resident) and
     # crash-looped at graph capture. The serve script keeps the opt-in flag.
     ! grep -q '^FRANK_PRIMARY_PRECISE_MEMORY=' "$ENV_FILE"
@@ -185,14 +192,12 @@ DOWNLOAD="$REPO_ROOT/scripts/download-frank-primary.sh"
     ! grep -q -- '--speculative-config' "$SERVE"
 }
 
-@test "KV dtype is bf16 (auto) — exactness, paid for in pool bytes" {
-    # --kv-cache-dtype auto = bf16 (unquantized). Frank's call 2026-10-01.
-    # bf16 costs 13,839 B/token against fp8's 7,701 — decomposed as 12,276
-    # attention + 1,563 mamba/side (dtype-independent) versus fp8's 6,138 +
-    # 1,563. That halves the pool capacity per byte, which is why the contract
-    # is two full-size windows instead of three; in exchange the KV is exact
-    # (no quantization error) and measured +4% decode at shallow depth, where
-    # fp8's dequant cost dominates over the extra bytes read.
+@test "KV dtype is fp8 — the incumbent, and the only one that boots" {
+    # fp8 costs 7,701 B/token, decomposed as 6,138 attention + 1,563
+    # mamba/side (dtype-independent); bf16 costs 13,839 (12,276 + 1,563).
+    # bf16 was abandoned 2026-10-01: its 2 x 262144 boot died with 0 bytes
+    # free on a real request, and the SEQS=2 slot count it was designed
+    # around cannot compile this model at all (see the shape test above).
     grep -q '^FRANK_PRIMARY_KV_DTYPE=fp8$' "$ENV_FILE"
     grep -q -- '--kv-cache-dtype "$FRANK_PRIMARY_KV_DTYPE"' "$SERVE"
 }
@@ -208,13 +213,14 @@ DOWNLOAD="$REPO_ROOT/scripts/download-frank-primary.sh"
     grep -q -- '-e R4D_LRU_GATHER_CHUNKS="$FRANK_PRIMARY_GATHER_CHUNKS"' "$SERVE"
 }
 
-@test "MNBT is at Frank's 2048 with the arena intact" {
+@test "MNBT is at Frank's 1024 with the arena intact" {
     # MNBT 512 doubles TTFT at 4064 ctx (2.46 s vs 1.36 s); 1024-4096 are
     # interchangeable on decode AND identical on arena (the sweep measured
     # 6,499 slots at every rung <=4096); 12288 costs 2.5% plus arena.
-    # 2048 is Frank's setting as of 2026-10-01 — it keeps the workspace floor
-    # so the expert arena stays max.
-    grep -q '^FRANK_PRIMARY_MNBT=2048$' "$ENV_FILE"
+    # 1024 is Frank's lock — it keeps the workspace floor so the expert arena
+    # stays max. (2026-10-02: MNBT 2048 compiles the first graph in 26 s vs
+    # 172 s at 1024 — a startup-cost lever, not a correctness one.)
+    grep -q '^FRANK_PRIMARY_MNBT=1024$' "$ENV_FILE"
     grep -q -- '--max-num-batched-tokens "$FRANK_PRIMARY_MNBT"' "$SERVE"
 }