diff --git a/docs/plans/2026-08-22-visualmaster-campaign.md b/docs/plans/2026-08-22-visualmaster-campaign.md
index 250215c5..ce2fc78a 100644
--- a/docs/plans/2026-08-22-visualmaster-campaign.md
+++ b/docs/plans/2026-08-22-visualmaster-campaign.md
@@ -46,6 +46,32 @@ AC-specific constants — a number without a decomp/DAT anchor gets a register
 row in the same commit — and the pack-off path is the oracle: any slice that
 moves a pack-off pixel outside its declared mask is a bug, not a tuning.
 
+## Lesson carried into every slice — a branch that exists is not a branch that runs
+
+VM2 found that Campaign AR's #226 port, the 2026-08-21 findings doc it was
+briefed from, and the AR review's "probably" were all describing the
+**fallback** branch of retail's detail pass — the `stage == 0` framebuffer
+blend that retail only takes when the adapter cannot advertise
+`D3DTEXOPCAPS_PREMODULATE`. Real hardware (the owner's AMD, and anything
+modern) takes the single-pass texture-stage branch, which computes a
+different formula with the opposite sign of effect (darkens, not brightens).
+The decomp was read correctly three times; what nobody did until VM2 was
+spend two minutes reading the capability on a live client.
+
+Binding rule for this campaign and after: **when retail gates a mechanism
+behind a capability, preference, or `trysinglepass`-style switch, the port
+is not done until the gate's live value is recorded** — a cdb read on the
+PDB-paired client, cited in the port's note with the binary GUID. "Grep
+named → decompile → port" answers what the code *says*; only the live read
+answers what it *does* on the hardware the game actually ran on. A guess
+about driver caps ("rarely advertised") is not evidence and must not appear
+in a review verdict.
+
+Corollary for brightness questions: the owner's live "too bright" (exposure
+1.0 → 0.80) was the pack-on gamma-space tonemap (F4, VM3), not this. The
+detail overlay's fallback brightening is +3 % on building shells only; the
+single-pass path darkens by ~10 %. Neither explains a scene-wide level.
+
 ## Slice ledger
 
 | Slice | Closes | Gate |