diff --git a/dirigo-results/0.2.13-port/intercept/trace/conf-q2_0.json b/dirigo-results/0.2.13-port/intercept/trace/conf-q2_0.json
new file mode 100644
index 00000000000..a702dada195
--- /dev/null
+++ b/dirigo-results/0.2.13-port/intercept/trace/conf-q2_0.json
@@ -0,0 +1,59 @@
+{
+ "exe": "/home/bob/bin/strata-sycl-host.sh",
+ "args": [
+  "--pack",
+  "/home/bob/strata-nvme/q2_0",
+  "--native",
+  "/media/bob/3d651e2c-e9a4-4758-ba77-863725fe3731/public/strata-gguf/Q2_0/Q2_0/Qwen3.8-Flash-Next-GSQ-RCO-Q2_0-00001-of-00002.gguf",
+  "--stream-experts",
+  "--expert-cache",
+  "12288",
+  "--prefill",
+  "auto",
+  "--prompt-cache",
+  "6",
+  "--prompt-cache-every",
+  "4096",
+  "--batch",
+  "0",
+  "--spec",
+  "6",
+  "--spec-min-p",
+  "0.5",
+  "--mtp",
+  "/home/bob/XeStrata-data/mtp/rt",
+  "--mtp-draft-vocab",
+  "/media/bob/3d651e2c-e9a4-4758-ba77-863725fe3731/strata-0.2.13/data/draft_vocab_en.bin",
+  "--mtp-window",
+  "8192",
+  "--max-context",
+  "131072",
+  "--kv",
+  "int8",
+  "--kv-resident",
+  "32768",
+  "--vram-reserve-mib",
+  "700",
+  "--conversation-cache-mib",
+  "2048"
+ ],
+ "cwd": "/media/bob/3d651e2c-e9a4-4758-ba77-863725fe3731/strata-0.2.13",
+ "tokenizer": "/home/bob/XeStrata-data/packs/coder-iq1_m/tokenizer",
+ "model_name": "qwen3.8-flash-next-coder-iq1_m",
+ "log": "/media/bob/3d651e2c-e9a4-4758-ba77-863725fe3731/strata-0.2.13/strata-q2_0-noprofile.log",
+ "port": 8095,
+ "backend": "sycl",
+ "open_browser": false,
+ "thinking_policy": "on",
+ "conv_route": "on",
+ "conv_route_batch_after": 4,
+ "short_answer": {
+  "spec": 0,
+  "max_tokens": 16
+ },
+ "spec_window": 0,
+ "spec_window_needle_min": 6000,
+ "code_tune": {
+  "mode": "off"
+ }
+}
\ No newline at end of file
diff --git a/dirigo-results/0.2.13-port/intercept/trace/conf-shadow.json b/dirigo-results/0.2.13-port/intercept/trace/conf-shadow.json
new file mode 100644
index 00000000000..99559601b21
--- /dev/null
+++ b/dirigo-results/0.2.13-port/intercept/trace/conf-shadow.json
@@ -0,0 +1,63 @@
+{
+ "exe": "/home/bob/bin/strata-sycl-host.sh",
+ "args": [
+  "--pack",
+  "/home/bob/XeStrata-data/packs/coder-iq1_m",
+  "--native",
+  "/home/bob/strata-models/IQ1_M/Qwen3.8-Flash-Next-GSQ-RCO-IQ1_M-00001-of-00002.gguf",
+  "--ple-gguf",
+  "/home/bob/strata-models/IQ1_M/Qwen3.8-Flash-Next-GSQ-RCO-IQ1_M-00002-of-00002.gguf",
+  "--expert-profile",
+  "/media/bob/3d651e2c-e9a4-4758-ba77-863725fe3731/strata-0.2.13/data/expert-profile-mine.bin",
+  "--expert-cache",
+  "auto",
+  "--stream-experts",
+  "--prefill",
+  "auto",
+  "--prompt-cache",
+  "6",
+  "--prompt-cache-every",
+  "4096",
+  "--batch",
+  "0",
+  "--spec",
+  "6",
+  "--spec-min-p",
+  "0.5",
+  "--mtp",
+  "/home/bob/XeStrata-data/mtp/rt",
+  "--mtp-draft-vocab",
+  "/media/bob/3d651e2c-e9a4-4758-ba77-863725fe3731/strata-0.2.13/data/draft_vocab_en.bin",
+  "--mtp-window",
+  "8192",
+  "--max-context",
+  "131072",
+  "--kv",
+  "int8",
+  "--kv-resident",
+  "32768",
+  "--vram-reserve-mib",
+  "700",
+  "--conversation-cache-mib",
+  "2048"
+ ],
+ "cwd": "/media/bob/3d651e2c-e9a4-4758-ba77-863725fe3731/strata-0.2.13",
+ "tokenizer": "/home/bob/XeStrata-data/packs/coder-iq1_m/tokenizer",
+ "model_name": "qwen3.8-flash-next-coder-iq1_m",
+ "log": "/media/bob/3d651e2c-e9a4-4758-ba77-863725fe3731/strata-0.2.13/strata-iq1_m-shadow.log",
+ "port": 8095,
+ "backend": "sycl",
+ "open_browser": false,
+ "thinking_policy": "on",
+ "conv_route": "shadow",
+ "conv_route_batch_after": 4,
+ "short_answer": {
+  "spec": 0,
+  "max_tokens": 16
+ },
+ "spec_window": 0,
+ "spec_window_needle_min": 6000,
+ "code_tune": {
+  "mode": "off"
+ }
+}
\ No newline at end of file
diff --git a/dirigo-results/0.2.13-port/intercept/trace/ladder-iq1_m.json b/dirigo-results/0.2.13-port/intercept/trace/ladder-iq1_m.json
new file mode 100644
index 00000000000..7f9cfa6579d
--- /dev/null
+++ b/dirigo-results/0.2.13-port/intercept/trace/ladder-iq1_m.json
@@ -0,0 +1,276 @@
+[
+ {
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+  "wall_ms": 623.6,
+  "prompt_tokens": 128,
+  "reused": 0,
+  "fresh": 128,
+  "prefill_ms": 544,
+  "prefill_tps": 235.5,
+  "decode_ms": 78,
+  "park_tokens": 96,
+  "park_ms": 103.1,
+  "kv_hit_pct": 91.35,
+  "kv_mib_from_ram": 1.6,
+  "server_ms": 20.7,
+  "label": "iq1_m"
+ },
+ {
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+  "park_tokens": 135,
+  "park_ms": 100.6,
+  "server_ms": 20.8,
+  "label": "iq1_m"
+ },
+ {
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+  "label": "iq1_m"
+ },
+ {
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+  "label": "iq1_m"
+ },
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+  "label": "iq1_m"
+ },
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+  "label": "iq1_m"
+ },
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+ },
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+ },
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+ },
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+ },
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+ },
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+ },
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+  "label": "iq1_m"
+ },
+ {
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+ },
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+  "label": "iq1_m"
+ },
+ {
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+  "kv_mib_from_ram": 19.6,
+  "server_ms": 27.8,
+  "label": "iq1_m"
+ }
+]
\ No newline at end of file
diff --git a/dirigo-results/0.2.13-port/intercept/trace/ladder-shadow.json b/dirigo-results/0.2.13-port/intercept/trace/ladder-shadow.json
new file mode 100644
index 00000000000..a0dc62c23bd
--- /dev/null
+++ b/dirigo-results/0.2.13-port/intercept/trace/ladder-shadow.json
@@ -0,0 +1,294 @@
+[
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+  "reused": 0,
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+  "park_tokens": 96,
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+ },
+ {
+  "target": 2048,
+  "ttft_ms": 1695.0,
+  "wall_ms": 1787.2,
+  "prompt_tokens": 1608,
+  "reused": 0,
+  "fresh": 1608,
+  "prefill_ms": 1671,
+  "prefill_tps": 962.5,
+  "decode_ms": 111,
+  "park_tokens": 1615,
+  "park_ms": 106.7,
+  "kv_hit_pct": 95.23,
+  "kv_mib_from_ram": 19.5,
+  "server_ms": 24.0,
+  "label": "shadow"
+ },
+ {
+  "target": 2048,
+  "ttft_ms": 1699.6,
+  "wall_ms": 1791.8,
+  "prompt_tokens": 1608,
+  "reused": 0,
+  "fresh": 1608,
+  "prefill_ms": 1675,
+  "prefill_tps": 960.0,
+  "decode_ms": 111,
+  "park_tokens": 1615,
+  "park_ms": 108.3,
+  "server_ms": 24.6,
+  "label": "shadow"
+ },
+ {
+  "target": 2048,
+  "ttft_ms": 1694.5,
+  "wall_ms": 1786.8,
+  "prompt_tokens": 1608,
+  "reused": 0,
+  "fresh": 1608,
+  "prefill_ms": 1670,
+  "prefill_tps": 963.1,
+  "decode_ms": 111,
+  "park_tokens": 1615,
+  "park_ms": 102.5,
+  "kv_hit_pct": 94.1,
+  "kv_mib_from_ram": 19.5,
+  "server_ms": 24.5,
+  "label": "shadow"
+ }
+]
\ No newline at end of file
diff --git a/dirigo-results/0.2.13-port/intercept/trace/strata-trace-split.py b/dirigo-results/0.2.13-port/intercept/trace/strata-trace-split.py
new file mode 100755
index 00000000000..18b9b494434
--- /dev/null
+++ b/dirigo-results/0.2.13-port/intercept/trace/strata-trace-split.py
@@ -0,0 +1,90 @@
+#!/usr/bin/env python3
+"""Split the per-request fixed cost using the engine's own STRATA_TRACE admission line.
+
+The engine prints, per admitted request:
+
+  strata trace: admission of slot 0: drain 0.0, prompt 402.1 (read 388.0, windows 11.2, 1 checkpoint(s) 2.1 =
+    sync 1.0 + save 0.8 + evict 0.3, rest 0.0), first window 0.0, slot copy 0.4, slot freed 0.0, checkpoint copy 0.1
+
+followed by the prompt line this probe already keys on. Pairing them by order gives the phases that make up the
+"fixed cost": what is spent before the prompt read (drain + slot work), what the read itself costs, and what follows.
+
+    ~/bin/strata-trace-split.py --log <engine log> [--since-bytes N] [--json out.json]
+
+Use --since-bytes <size of the log before the run> to ignore earlier requests, or just parse the whole log and read
+the tail of the table (the run's own requests are the last ones).
+"""
+import argparse
+import json
+import re
+import statistics as st
+
+RE_TRACE = re.compile(
+    r"strata trace: admission of slot (\d+): drain ([\d.]+), prompt ([\d.]+) "
+    r"\(read ([\d.]+), windows ([\d.]+), (\d+) checkpoint\(s\) ([\d.]+) = sync ([\d.]+) \+ save ([\d.]+) \+ "
+    r"evict ([\d.]+), rest ([\d.]+)\), first window ([\d.]+), slot copy ([\d.]+), slot freed ([\d.]+), "
+    r"checkpoint copy ([\d.]+)")
+RE_PROMPT = re.compile(r"strata serve: prompt (\d+) tokens = (\d+) reused \+ (\d+) read in (\d+) ms")
+PHASES = ("drain", "prompt", "read", "windows", "ckpts", "sync", "save", "evict", "rest",
+          "first_window", "slot_copy", "slot_freed", "ckpt_copy")
+
+
+def parse(path, since=0):
+    with open(path, "rb") as f:
+        f.seek(since)
+        text = f.read().decode("utf-8", "replace")
+    rows, pending = [], None
+    for line in text.splitlines():
+        m = RE_TRACE.search(line)
+        if m:
+            g = m.groups()
+            pending = dict(slot=int(g[0]), prompt_ms=float(g[2]), read=float(g[3]), windows=float(g[4]),
+                           ckpts=int(g[5]), ckpt_ms=float(g[6]), sync=float(g[7]), save=float(g[8]),
+                           evict=float(g[9]), rest=float(g[10]), first_window=float(g[11]),
+                           slot_copy=float(g[12]), slot_freed=float(g[13]), ckpt_copy=float(g[14]))
+            pending["drain"] = float(g[1])
+            continue
+        p = RE_PROMPT.search(line)
+        if p and pending is not None:
+            pending.update(prompt_tokens=int(p.group(1)), reused=int(p.group(2)), read_n=int(p.group(3)),
+                           engine_prefill_ms=float(p.group(4)))
+            rows.append(pending)
+            pending = None
+    return rows
+
+
+def main():
+    ap = argparse.ArgumentParser()
+    ap.add_argument("--log", required=True)
+    ap.add_argument("--since-bytes", type=int, default=0)
+    ap.add_argument("--json")
+    args = ap.parse_args()
+    rows = parse(args.log, args.since_bytes)
+    if not rows:
+        print("no trace admission lines paired with a prompt line - was STRATA_TRACE set for the ENGINE process?")
+        return
+    print(f"{len(rows)} request(s) traced\n")
+    hdr = f"{'tokens':>7} {'reused':>7} {'prefill':>8} " + " ".join(f"{p:>11}" for p in PHASES)
+    print(hdr)
+    print("-" * len(hdr))
+    for r in rows:
+        print(f"{r['prompt_tokens']:>7} {r['reused']:>7} {r['engine_prefill_ms']:>8.0f} " +
+              " ".join(f"{r[p]:>11.1f}" for p in PHASES))
+    # per-size medians, and the share of the fixed cost each phase owns
+    print("\nper-size median of the admission phases (ms), for requests that read their prompt (reused == 0):")
+    for size in sorted({r["prompt_tokens"] for r in rows}):
+        grp = [r for r in rows if r["prompt_tokens"] == size and r["reused"] == 0]
+        if len(grp) < 2:
+            continue
+        med = {p: st.median([r[p] for r in grp]) for p in PHASES}
+        med["n"] = len(grp)
+        print(f"  {size:>6} tok (n={med['n']}): " +
+              "  ".join(f"{p} {med[p]:.1f}" for p in ("drain", "slot_copy", "slot_freed", "read", "windows",
+                                                      "ckpts", "rest", "first_window", "ckpt_copy", "prompt")))
+    if args.json:
+        json.dump(rows, open(args.json, "w"), indent=1)
+        print(f"\nwrote {args.json}")
+
+
+if __name__ == "__main__":
+    main()
diff --git a/dirigo-results/0.2.13-port/intercept/trace/strata-trace-window.sh b/dirigo-results/0.2.13-port/intercept/trace/strata-trace-window.sh
new file mode 100755
index 00000000000..2ce0b25bb0e
--- /dev/null
+++ b/dirigo-results/0.2.13-port/intercept/trace/strata-trace-window.sh
@@ -0,0 +1,35 @@
+#!/usr/bin/env bash
+# strata-trace-window.sh - run the ladder with the engine's own STRATA_TRACE and split the fixed cost.
+#
+# The 0.2.13 engine already prints a per-request admission trace (drain, prompt read, windows, checkpoints, first
+# window, slot copy, slot freed, checkpoint copy) when STRATA_TRACE is set, so no build is needed to ask which phase
+# owns the ~165 ms that section 6 of docs/PERF-NEXT.md left unnamed.
+#
+# Six samples per size so each size is measured in BOTH router states: with batch_after 4 the first four requests of a
+# run are served cache-on, the fifth onward cache-off.
+#
+# usage: strata-trace-window.sh [tag] [sizes] [samples]
+# UNDO: rm this file and ~/strata-trace-run
+set -uo pipefail
+TAG=${1:-iq1_m}
+SIZES=${2:-75,512,2048}
+SAMPLES=${3:-6}
+CONF=${CONF:-$TREE/strata-coder-iq1_m-sycl-tuned.json}   # CONF=... for a different pack/weights
+S=/media/bob/3d651e2c-e9a4-4758-ba77-863725fe3731
+TREE=$S/strata-0.2.13
+OUT=$HOME/strata-trace-run
+PROBE=$HOME/bin/strata-intercept-probe.py
+SPLIT=$HOME/bin/strata-trace-split.py
+mkdir -p "$OUT"
+
+echo "[$(date +%H:%M:%S)] ===== trace-$TAG sizes=$SIZES samples=$SAMPLES"
+STRATA_TRACE=1 ~/bin/strata-card-window.sh "$TREE" 8097 --conf "$CONF" -- bash -c "
+    LOG=\$(python3 -c \"import json;print(json.load(open('$CONF'))['log'])\")
+    curl -s -m 5 http://127.0.0.1:\$PORT/v1/status | python3 -c 'import json,sys;d=json.load(sys.stdin);print(\"  engine:\",d[\"engine\"])'
+    BEFORE=\$(stat -c%s \"\$LOG\")
+    /usr/bin/python3 $PROBE --port \$PORT --log \"\$LOG\" --out $OUT/ladder-$TAG.json --label $TAG \
+        --sizes $SIZES --samples $SAMPLES
+    /usr/bin/python3 $SPLIT --log \"\$LOG\" --since-bytes \$BEFORE --json $OUT/trace-$TAG.json
+    cp \"\$LOG\" $OUT/engine-$TAG.log
+" 2>&1 | grep -aE '=====|engine:|tok \(|^ +[0-9]+ +[0-9]+|request\(s\) traced|wrote|restore|no trace'
+echo "[$(date +%H:%M:%S)] trace window done"
diff --git a/docs/PERF-NEXT.md b/docs/PERF-NEXT.md
index fef3028a35e..f1b8dddcaf1 100644
--- a/docs/PERF-NEXT.md
+++ b/docs/PERF-NEXT.md
@@ -51,14 +51,15 @@ fixed term.
 
 | # | idea | evidence it could pay | cost | first test |
 | --- | --- | --- | --- | --- |
-| 1 | ~~ship `conv-route-batch-after` 1–2~~ | **closed, keep 4.** §7: 1 buys 0.52 s across the first six single-shot requests and costs **1.88 s** on the next conversation turn (`C2` 2.465 s against 0.587) — break-even at ~21 single-shots per conversation re-open | — | done; the config key that would have set it was also dead (PR #16) |
-| 2 | engine-side per-request timer | §6 leaves **~165 ms** inside prefill that no configuration lever explains (PLE reads excluded, cache slots ~58 ms of it); naming it needs a phase timer in the request path | code, a day | timestamp slot setup / first-layer expert reach / KV alloc per request |
-| 3 | ~~a one-shot mode that also drops the cache slots~~ | **closed, §8**: no saving over the router's cache-off path at matched sizes (+2 ms at 456 tokens, +8 ms at 1,608), and a 0-slot start severs conversation reuse for good — every turn re-prefilled | — | done |
-| 4 | residency-biased router on SYCL | `route_prior.cu` is CUDA-only; here **12,288 of 24,576** experts are resident, so half of every token's experts cross PCIe. Upstream measured +15 % / +37 % on a 12 GB NVIDIA card | engine port, days | decode lanes, 5 interleaved pairs |
-| 5 | prefill chunk at 4k/8k/12k with intervals | 16k/32k were tested, but 8,192 was never shown to be the knee | ~20 min | paired, three prompt sizes, per-prompt medians |
-| 6 | CPU pool workers and affinity on the 7700X | 15 workers is a 16-thread default; p-core pinning was **+27 %** decode on the 13700K | 15 min | workers 8/12/15/16, `--pool-affinity` on/off |
-| 7 | dispatch overhead on SYCL | the Vulkan analysis found ~88 % of per-dispatch cost is fixed; nobody has counted dispatches per token on SYCL | a day | `unitrace` kernel count per token, then fuse the five most frequent small ops |
-| 8 | DFlash2 block drafter on SYCL | upstream's headline decode lever; 7 drafts per pass | weeks | only after 1–3 |
+| 1 | **defer the slot refill past the first token** | §9: the refill runs between the prompt read and `prompt done` at **0.319 ms per lent slot** — 72 ms on a 127-token prompt, 188 ms on a 1.6 k one, on the TTFT path. Decode needs its own experts, not the slots being refilled | engine change, a few lines | the same ladder with the refill moved; watch for PCIe contention with decode |
+| 2 | ~~ship `conv-route-batch-after` 1–2~~ | **closed, keep 4.** §7: 1 buys 0.52 s across the first six single-shot requests and costs **1.88 s** on the next conversation turn (`C2` 2.465 s against 0.587) — break-even at ~21 single-shots per conversation re-open | — | done; the config key that would have set it was also dead (PR #16) |
+| 3 | ~~engine-side per-request timer~~ | **done, no build**: `STRATA_TRACE` already splits the prompt path — §9 names 109 ms of read-side fixed work, 72 ms of refill and 56 ms of bookkeeping | — | done |
+| 4 | ~~a one-shot mode that also drops the cache slots~~ | **closed, §8**: no saving over the router's cache-off path at matched sizes (+2 ms at 456 tokens, +8 ms at 1,608), and a 0-slot start severs conversation reuse for good — every turn re-prefilled | — | done |
+| 5 | residency-biased router on SYCL | `route_prior.cu` is CUDA-only; here **12,288 of 24,576** experts are resident, so half of every token's experts cross PCIe. Upstream measured +15 % / +37 % on a 12 GB NVIDIA card | engine port, days | decode lanes, 5 interleaved pairs |
+| 6 | prefill chunk at 4k/8k/12k with intervals | 16k/32k were tested, but 8,192 was never shown to be the knee | ~20 min | paired, three prompt sizes, per-prompt medians |
+| 7 | CPU pool workers and affinity on the 7700X | 15 workers is a 16-thread default; p-core pinning was **+27 %** decode on the 13700K | 15 min | workers 8/12/15/16, `--pool-affinity` on/off |
+| 8 | dispatch overhead on SYCL | the Vulkan analysis found ~88 % of per-dispatch cost is fixed; nobody has counted dispatches per token on SYCL | a day | `unitrace` kernel count per token, then fuse the five most frequent small ops |
+| 9 | DFlash2 block drafter on SYCL | upstream's headline decode lever; 7 drafts per pass | weeks | only after 1–3 |
 
 ## 5. The PLE sweep, run 2026-11-14 — closed
 
@@ -110,8 +111,8 @@ on, like stock) — client TTFT from the first content delta, and the engine's o
    profile is equal — 456 tokens: 539.7 against 537.3; 1,608 tokens: 1,471.3 against 1,463.3.
 5. **The draft layer could not be switched off to test its share**: `--spec 0` is refused on a native IQ pack, which
    needs `--spec T (T >= 2)`.
-6. **What is left is ~165 ms** inside prefill after the cache slots' ~58 ms, unexplained by any configuration lever
-   tried so far (PLE row reads are excluded by §5). Naming it needs a phase timer inside the request path.
+6. **The ~165 ms is now split, without a build** — the engine already prints a per-request trace under `STRATA_TRACE`:
+   ~109 ms of fixed work inside the prompt read, ~72 ms of expert-slot refill, ~56 ms of cache bookkeeping. See §9.
 
 Artifacts: [`0.2.13-port/intercept/`](../dirigo-results/0.2.13-port/intercept/) — both ladders, the three
 cause-sweep arms, `summary.json`, the probe and both drivers, and the logs with every restore line.
@@ -180,7 +181,55 @@ path, which means a build.
 Artifacts: [`0.2.13-port/intercept/zerocache/`](../dirigo-results/0.2.13-port/intercept/zerocache/) — both ladders, the
 mixed shape, the configs, the driver, and the window log with every restore line.
 
-## 9. Method rules these numbers were produced under
+## 9. Where the ~165 ms goes: the expert-slot refill
+
+`STRATA_TRACE=1` makes engine 0.1.59 print the prompt path per request — `prompt start`, `lent N slots`, `prompt chunk`,
+`read N tokens in X ms`, `refill start`, `refilled N slots in X ms`, `prompt done`. No build is needed to read it. (The
+per-request *admission* trace needs `--batch`, so with `--batch 0` it stays silent; the prompt path is what matters here.)
+
+Ladder with the deployed router, six samples per size, medians:
+
+| real tokens | read | refill | lent slots | refill per slot |
+| --- | --- | --- | --- | --- |
+| 127 | 252 ms | **71.7 ms** | 225 | 0.319 |
+| 457 | 432 ms | **82.6 ms** | 259 | 0.319 |
+| 1,609 | 1,245 ms | **188.2 ms** | 589 | 0.320 |
+
+1. **The refill is a fixed per-request cost on the TTFT path.** It runs *after* the prompt read and *before* `prompt
+   done`, so the first token waits for it: 72 ms on a short prompt, 188 ms on a 1.6 k one.
+2. **It is one PCIe transfer per lent expert slot at 0.319 ms/slot** — the same rate at all three sizes to within 0.3 %.
+   The prompt borrows expert slots while it reads; afterwards the engine refills them with the profile's hottest experts.
+3. **The read itself carries 109 ms of fixed work** (`109 ms + 0.706 ms/token` over the three sizes): first-layer expert
+   reach and chunk setup, plus ~56 ms of cache bookkeeping. 109 + 72 + 56 ≈ the 165 ms §6 could not name, leaving
+   nothing unexplained at this resolution.
+4. **This reconciles §6 with the dispatch.** Pinning the cache on (`conv_route: shadow`) raises TTFT by 148–234 ms but
+   raises `read + refill` by only 7–29 ms: the cache-on cost is checkpoint work inside the engine's prompt span, not in
+   the prompt read. Both measurements were right about different parts of the same 200 ms.
+
+**The lever this exposes:** the refill does not have to be synchronous with the answer. It reclaims slots the *next*
+request will lend again, and decode for the current request needs its own experts, not those slots. Moving it after the
+first token would take 72–188 ms off TTFT — the largest remaining cheap win, and it is an engine change of a few lines
+rather than a research project.
+
+Artifacts: [`0.2.13-port/intercept/trace/`](../dirigo-results/0.2.13-port/intercept/trace/) — both ladders, the engine
+logs with every trace line, the parser and the window driver.
+
+### Cross-weight check: blocked, three engine constraints
+
+The same trace was attempted on a second weight set (the Q2_0 pack, 34 GB, copied to NVMe from the cold disk for this)
+and could not start:
+
+| attempt | engine's answer |
+| --- | --- |
+| Q2_0 pack + `--ple-gguf` at the shared PLE shard | `native dense: duplicate split shard number` |
+| pack only, embedding from the GGUF, no `--native` | `is a native (IQ) pack: it needs --native SHARD1, --spec T (T >= 2) and --prefill CHUNK` |
+| fixed `--expert-cache 12288`, no profile | `REFUSED: 11158 experts are neither in VRAM nor mirrored` |
+
+The shipped `expert-profile-mine.bin` is 48×256 and the Q2_0 pack declares 48×512, so the second weight set needs its
+own calibration run before it can serve. Until then every number in this inventory stands on one weight set (IQ1_M),
+which is stated in §10 and is the honest bound on all of it.
+
+## 10. Method rules these numbers were produced under
 
 - Paired or interleaved arms; median of repeats; the box's run-to-run spread stated next to the effect.
 - One prompt per configuration is not a measurement: every lane here has several requests, and a single-prompt