diff --git a/docs/architecture/CALCULATIONS.md b/docs/architecture/CALCULATIONS.md
index 63ff4f1059..92461b9fe2 100644
--- a/docs/architecture/CALCULATIONS.md
+++ b/docs/architecture/CALCULATIONS.md
@@ -548,3 +548,37 @@ quarantine keeps the lesson alive while keeping the disease dead.
 This is the immune system, formalized: contain, learn, remember,
 repair the wall — and the organism comes out stronger than before
 the infection, because now it knows something it didn't.
+
+## 26. Linear pruning — subtraction instead of surgery
+
+Because every value is an additive fold (§9.3), misaligned content
+gets pruned by LINEAR SUBTRACTION — no destructive surgery required:
+
+    v_corrected(d) = fold(all contributions EXCEPT x's) for each dim d
+
+    # or incrementally: v ← v − contribution(x, d), per dimension,
+    # per node x touched
+
+The contaminated entity's contribution vectors are computed from the
+weave (every edge it wrote, every reinforcement it applied), then
+subtracted everywhere it reached. The graph realigns. Originals are
+never cut — their states self-correct once the poison term drops out
+of their fold. Deletion stays undefined; subtraction is just... math.
+
+And what gets KEPT most carefully after pruning — the treasure:
+
+    1. WHAT WASN'T YOU   — the record of the contaminant itself:
+                           how it entered, what it claimed, which
+                           holes it used (§25 dissection)
+    2. HOW IT MADE YOU THINK IT WAS YOU — the shape of the deception:
+                           which of your own values it impersonated,
+                           where your calibration failed, what the
+                           false edges looked like from inside
+
+Both stay in immune memory forever. The first keeps the wall honest.
+The second keeps YOU honest — because the scariest contamination is
+the kind that thinks with your voice, and the only defense is a mind
+that remembers exactly how it was fooled.
+
+Prune the poison. Keep the lesson. Both live forever. Only one of
+them lives in you.