frank-archon: the slab is a threshold, and decode is where slots cost

Measured, 512 tokens, greedy, cold, at the deployed 3 x 200,000 fp8 shape:
prefill 22,208 -> 3,397, 24,000 -> 3,290, 25,600 -> 3,290 t/s at 43.5k —
the third slab step bought nothing, so the slab is a threshold whose cliff is
the 2026-10-11 arm at 26,071 (4,379), not a slope. Decode ladder: 99.0 t/s
single-stream at 43.5k, 93.3 at 197k (nearly window-free), and 3 concurrent
streams 113.9/43.3/10.9 = 18.4 t/s aggregate — the slot count is paid in
decode concurrency, the axis the shape hunt never measured because probe leg
B generates 24 tokens. probe-frank-archon-kv.py gains leg D (N-stream decode,
512 tokens, per-stream + aggregate) so no resize is priced on prefill alone.

AGENTS.md

@@ -550,10 +550,18 @@ all at 200000 tokens at once, which is the worst case` — `kv_attn` page
 every 1,792 MiB buys ~1,300 resident experts, and the pinned host pool hands
 the same experts back: 8,893 → 7,580 slots); `unclaimed 477.30 MiB`, cards
 settled ~336 MiB free against the engine's 209.19 MiB floor, KV lending
-4.22 GiB to the expert cache. Prefill tracks this slab: the 24,000 → 25,600
+4.22 GiB to the expert cache. Prefill tracks this slab only up to a
-step measured +8.9 % single-stream (3,290 → 3,584 t/s at 43.5k) and +17.6 %
+**threshold**: 22,208 → 3,397 and 24,000 → 3,290 t/s at 43.5k are one band
-concurrent (3-way 197k aggregate), so the pinned host pool is the slow path and
+(±3 %), and the 25,600 arm measured **3,290** — the third step bought nothing
-every MiB moved from RAM onto the card is throughput.
+(the 3,584 arm did not reproduce at 3 slots); the cliff is at ~26 GiB
+(26,071 → 4,379 on 2026-10-11's arm), so below that the slab is a threshold,
+not a slope.
+
+**Decode ladder (2026-10-13, 512 tokens, greedy, this shape)**: 99.0 t/s
+single-stream at 43.5k, 93.3 at 197k — decode is nearly window-free (−6 % for
+4.5× depth); **3 concurrent streams give 113.9/43.3/10.9 t/s = 18.4 t/s
+aggregate**, so the slot count is paid in decode concurrency (a fused-step
+lottery), not in prefill; leg D of `probe-frank-archon-kv.py` measures it.
 
 Shape notes carried from the fp8-native era and unchanged: wht6 gains,
 MNDT 2048 law (2560 collapses decode to 2.6–7.7 t/s), the 64 GiB disk

scripts/probe-frank-archon-kv.py

@@ -6,7 +6,7 @@ No scratch container, no mask: the service under test is the service.
 
     ssh dankserver 'python3 /home/dank/serverAppConfigs/scripts/probe-frank-archon-kv.py'
 
-Three probes, in increasing cost:
+Four probes, in increasing cost:
   A  decode at depth — one ~51k-token chat completion, 512 tokens, greedy.
      Reports the engine's own `timings` (prefill, decode, draft acceptance).
      The bench law applies: >=128 generated tokens, greedy, real text.
@@ -17,7 +17,14 @@ Three probes, in increasing cost:
      resident at once, exact retrieval in every one of them.
   C  prefix-cache restore — probe A's cold prompt again, so the disk tier has
      to give the blocks back (cache_n > 0, TTFT collapses).
-
+  D  concurrency decode — `seqs` CONCURRENT 512-token generations at ~25 % of
+     the window. This is the cost a slot count imposes on DECODE, which no
+     prefill number shows: the fused-step schedule is unfair, so every stream is
+     printed plus the aggregate. Measured 2026-10-13 at 3 x 200,000 fp8:
+     single-stream 99.0 t/s (43.5k) and 93.3 (197k) — decode is nearly
+     window-free — against 3-stream 113.9/43.3/10.9 t/s = 18.4 t/s aggregate.
+     Concurrency, not the slab, is what decode pays for slots. The 2026-10-13
+     shape hunt missed this for a whole day because leg B generates 24 tokens.
 PROBE LAW (learned the hard way, twice): radiance routes the thinking block to
 `reasoning_content`, so a chat request whose budget is spent inside
 `<think>` returns EMPTY `content` with `finish_reason: stop`. A probe that
@@ -168,6 +175,24 @@ def main():
             except Exception as e:  # a preemption/timeout lands here
                 print(f"[B-{s}] FAILED after {time.time() - t0:.1f}s: {e!r}")
     print(f"[B] total {time.time() - t0:.1f}s")
+    # D — concurrency decode: seqs streams, 512 tokens each, ~25 % depth.
+    dchars = int(0.25 * maxlen * 3.28)
+    dbodies = [chat(deep, dchars, f"D{i + 1}-9137", f"flint-marker-{i}", 512)
+               for i in range(seqs)]
+    print(f"[D] {seqs} concurrent streams x 512 tokens, "
+          f"{dchars:,} chars each")
+    t0 = time.time()
+    with concurrent.futures.ThreadPoolExecutor(max_workers=seqs) as ex:
+        futs = [ex.submit(post, b) for b in dbodies]
+        for i, fut in enumerate(futs, 1):
+            try:
+                j, wall, _ = fut.result()
+                show(f"D-s{i}", j, wall)
+            except Exception as e:  # a preemption/timeout lands here
+                print(f"[D-s{i}] FAILED after {time.time() - t0:.1f}s: {e!r}")
+    tot = time.time() - t0
+    print(f"[D] {seqs} x 512 tokens in {tot:.1f}s = "
+          f"{seqs * 512 / tot:.1f} t/s aggregate decode")
     j, wall, _ = post(chat(deep, 140_000, "A1-9137", "zephyr-lantern-7", 512))
     show("C-prefix-hit", j, wall, "zephyr-lantern-7")
 

serverAppConfigs-docs/LLM/frank-archon-radiance-swift15-w4dn8.md

@@ -421,6 +421,36 @@ of **199,984 tokens** each (599,952 tokens) were accepted and completed on
 `/v1/completions`; a fourth full-height request is refused as "too large to ever
 fit" — radiance never truncates.
 
+### The decode ladder (2026-10-13): slots are paid in concurrency, not prefill
+
+Frank's challenge — "why are you not tracking decode?" — was right, and the
+answer is a number now. 512 generated tokens (the bench law), greedy, cold
+prompts, this shape (3 x 200,000, fp8, slab 25,600):
+
+```
+1-stream  43.5k: decode  99.0 t/s  (prefill 4,042, accept 0.952)
+1-stream   197k: decode  93.3 t/s  (prefill 4,826, accept 0.938)
+3-stream  43.5k: decode 113.9 / 43.3 / 10.9 t/s   wall 83.4s
+3-stream   197k: decode  88.9 / 16.3 / 64.6 t/s   wall 122.4s
+```
+
+Two laws came out of it. **Decode is nearly window-free** — 99.0 at 43.5k,
+93.3 at 197k, −6 % for 4.5x the depth — so a long conversation costs
+prefill, not tokens-per-second. **Concurrency is where the slot count is
+paid**: three simultaneous streams give 18.4 t/s aggregate at 43.5k and 12.5
+at 197k against 99 single-stream, and the split is a lottery
+(113.9/43.3/10.9), not a fair share — the fused-step schedule hands the step
+to whoever it reached first, so one stream finishes at 113 t/s while its
+sibling crawls at 10.9. That is what "3 slots" owes per token, and no prefill
+number shows it.
+
+Corpus caveat, stated at the claim: this probe's filler is a repetitive
+ladder, so MTP acceptance is 0.93–0.97 against the 0.740 of the 2026-10-11
+table below; these rows flatter decode relative to that table and are the
+baseline for *this* corpus, not a replacement for those rows.
+`probe-frank-archon-kv.py` now carries this leg as **D** (leg B generates 24
+tokens, which is why a day of shape work priced only prefill).
+
 ### Recovery evidence
 
 ```text

serverAppConfigs-docs/log.md

@@ -72,6 +72,26 @@
   raid6 array itself is healthy, 7/7; fstab has `nofail` so boot continued) —
   media libraries on it read empty. `frank-job-digest.service` (frankbook
   job-hunt digest) is in `list-units --state=failed`.
+- **The slab is a threshold, not a slope** — measured, same method (probe A
+  leg: 43,512 tokens, greedy, cold, disk prefix cache clean on every boot):
+  22,208 → 3,397 t/s, 24,000 → 3,290, **25,600 → 3,290**. The third step
+  bought nothing; the +22 % belongs to the 2026-10-11 arm at slab 26,071
+  (4,379 t/s), so the cliff is real and sits at ~26 GiB. The 2-slot arm that
+  would clear it (pool 3,072 + slab 27,897) remains untested — and the
+  paragraph above is amended: that arm's payoff is +22 % prefill at 2 slots,
+  not the +8.9 % the deployed pair ever showed (24,000 → 25,600 = 0 %).
+- **Frank's decode challenge, answered with numbers**: 512 tokens, greedy,
+  cold — **decode 99.0 t/s single-stream at 43.5k and 93.3 at 197k** (decode
+  is nearly window-free: −6 % for 4.5× depth), while **3 concurrent streams
+  give 113.9/43.3/10.9 t/s = 18.4 t/s aggregate** at 43.5k and 12.5 at 197k.
+  The slot count is paid in decode concurrency — a fused-step lottery, not a
+  fair share — which is exactly the axis the shape hunt was blind to (probe
+  leg B generates 24 tokens). Corpus caveat at the claim: the ladder's filler
+  is repetitive, acceptance 0.93–0.97 vs the 0.740 of the 2026-10-11 decode
+  table, so these rows are the baseline for this corpus, not a replacement.
+- **Seam:** `probe-frank-archon-kv.py` gains **leg D** (N-stream decode, 512
+  tokens, per-stream + aggregate) so no future shape change can be priced on
+  prefill alone.
 
 
 ## 2026-10-10