diff --git a/references/briefs.md b/references/briefs.md
index 71c3a4c..7dd04af 100644
--- a/references/briefs.md
+++ b/references/briefs.md
@@ -297,6 +297,15 @@ Falsify specifically:
   only agree with its author>
 - rerun the builds, tests and captures yourself
 
+Before recommending a mechanism as the fix direction, check that it was not
+already built and deleted. Run `git log -S '<distinctive identifier>'` and
+`git log --grep` on the owner's files, and read the scars in SKILL.md. If it
+was tried, cite the commit that removed it and say why the new situation
+differs, or recommend something else. (2026-09-30: a Soul pass recommended
+writer-thread ordered delivery in CultCache. That scheduler was built in
+`bcae483` and deleted in `4562340`, 34 minutes later, for deadlocking, and
+Imagination re-proved the deadlock.)
+
 Rerun the mutation tool on the range yourself; do not trust Hands' survivor
 triage. Challenge each "equivalent" call that is not a float boundary flip:
 measure it, as a mutant that changes how a thing is built can leave what it
diff --git a/references/changelog.md b/references/changelog.md
index c733314..1493591 100644
--- a/references/changelog.md
+++ b/references/changelog.md
@@ -1143,3 +1143,12 @@ code path", and "such obviously unnecessary split authority should never pass a
   what a reasonable consumer would expect. The call-count audit bounds only internal duplication.
 - The root cause was the skill's own "count real use … a surface with no consumer is parked" rule. It
   was written for app-internal subtraction and read as licence to trim library capability.
+
+## 2026-09-30: Soul checks history before recommending a mechanism
+
+- Evidence: CultNet publish, Soul pass 3, recommended ordered delivery inside CultCache's publication, on the
+  writer's thread. Imagination found that exact scheduler in `bcae483`, deleted in `4562340` 34 minutes later
+  for deadlocking against `_lifecycleGate`. A prototype re-proved the deadlock. SKILL.md already recorded
+  "design order as data, not as scheduling", and the brief carried no instruction to check.
+- The Soul brief template now requires `git log -S` / `--grep` on a mechanism before recommending it. A
+  mechanism that was tried must be cited with the reason the new situation differs.