diff --git a/campaign/backlog.md b/campaign/backlog.md
index fc384a9..dbaeb09 100644
--- a/campaign/backlog.md
+++ b/campaign/backlog.md
@@ -148,6 +148,15 @@ it fails if a corpus test skips.
 
 ### Track 1 — displacement: `compared → replaced`, then `modelled → compared`
 
+**Pick the replace unit by its WRITE SET, not by its name.** Lane CR's failure is the rule's
+source: our code replaced `ProcessResearch` and produced **all 13** tech-tree leaves the turn moves
+— the model was right — and the oracle still missed by 16, every one written by
+`OnTechResearched`, a neighbouring function. A replace boundary that splits a write set cannot
+pass an oracle no matter how correct the model is. So before attempting one, enumerate the leaves
+the turn moves in that area and ask which functions write them; if the answer is more than one,
+the unit is the union or the attempt is wasted. The compare mode's guard spans already name the
+write set — CR's five spans predicted exactly the five fields the oracle later billed.
+
 Only `replaced` means the original's code did not run. The bar, written once: an un-instrumented
 oracle first (`certified-pairs.md` format), then the same procedure with the hook in `replace`
 mode and the **same hashes**, with a count from the hook proving the path executed (rule 1).