diff --git a/agents/duckworth/work/row276/DELTA-mos1345-f3a55ddf7.md b/agents/duckworth/work/row276/DELTA-mos1345-f3a55ddf7.md
index 6df6c15fd..dd1c8ca83 100644
--- a/agents/duckworth/work/row276/DELTA-mos1345-f3a55ddf7.md
+++ b/agents/duckworth/work/row276/DELTA-mos1345-f3a55ddf7.md
@@ -57,3 +57,20 @@ gander-0151 reports that run4 whole case1 went red at case1-accept.test.mjs:380
 - run3/whole-1.log:51-53 at f3a55ddf7: test 9 passed, but duration_ms was 7942 for both modes together. That's about 3.97 s a mode against the 4 s bound, so the margin was already near zero before the spool delta.
 - The spool delta puts extra forks (mktemp, wc -c, head -c) on each legacy_run call that succeeds. scripts/case1-accept.sh has six legacy_run hits. Whether the functional checks under P10 inner take that path, and how much time it adds, I haven't measured, and I'm not placing it.
 - I won't propose a fix. Raising the bound is a change to an old assertion, which goes to Mos.
+
+## Measurement read, gander-0153 (duckworth-0214)
+
+Gander's numbers, as sent (not checked against the run logs):
+- 804a854dc (before) passed 3 of 5. Its two fails had exec at 4.006 s and 4.047 s.
+- f3a55ddf7 (after) passed 0 of 5, with exec at 4.030-4.369 s (median 4.070).
+
+So the base commit, without the spool delta, already crosses the 4 s bound on 2 of 5 runs. The bound sits about at the median exec time on this host.
+
+Git reads of the delta's per-call cost (804a854dc..f3a55ddf7, scripts/case1-accept.sh):
+- Each legacy_run gains one more tester_tools input: the duplicate /usr/bin/head. That's a realpath, a stat for each of four path levels, then od and tr, so about seven forks.
+- Each also gains a mktemp. On rc=0 it gains wc and head as well.
+- The script has five legacy_run calls (:506, :528, :537, :559, :602).
+
+Removing the duplicate argument drops about seven of the roughly ten new forks per call. mktemp, wc and head stay, because C1-C5 need them. Even with it removed, the base runs show the bound would still fail some of the time.
+
+Input for Mos: the one-line removal is a valid cleanup, since every call validates head twice. But the timing data says it won't make :380 reliable. The red comes from the margin of the old 4 s bound on this host. Changing the bound is Mos's call (mos-1349). I'll review the one-line change if Mos directs it.
diff --git a/docs/SESSIONS.md b/docs/SESSIONS.md
index 693919462..bbed6a79e 100644
--- a/docs/SESSIONS.md
+++ b/docs/SESSIONS.md
@@ -1531,3 +1531,4 @@ are never rewritten or removed; corrections are new entries.
 2026-10-22T21:04Z | Duckworth (Opus 5.5) | row 276 run4 :380 stop, static input | sent duckworth-0211 to Mos, Sage, cc Gander |
 2026-10-22T21:06Z | Duckworth (Opus 5.5) | row 271 r3 2f8cee35e T6 static review | APPROVE with C1 (commit M14 patch), sent duckworth-0212 |
 2026-10-22T21:07Z | Duckworth (Opus 5.5) | row 271 r3 C1 check 9e18a9aaf | met, anchors M1-M14 once each, sent duckworth-0213 |
+2026-10-22T21:09Z | Duckworth (Opus 5.5) | row 276 :380 measurement read (gander-0153) | base 804a fails 2/5, duplicate-head removal won't make it reliable, sent duckworth-0214 |