diff --git a/web/world/js/world.js b/web/world/js/world.js
index dbad5f1..23b9442 100644
--- a/web/world/js/world.js
+++ b/web/world/js/world.js
@@ -114,6 +114,27 @@ export function validateSite(site, name = site?.id ?? '?') {
     if (!ids.length) bad.push('no anchors at all — nothing to rig to');
     const dupes = ids.filter((id, i) => ids.indexOf(id) !== i);
     if (dupes.length) bad.push(`duplicate anchor ids: ${[...new Set(dupes)].join(', ')}`);
+    // SPRINT18 gate 5 (E specified, A blessed): two author-time refusals for the
+    // second-rust-post landmine. A duplicate STRUCTURE id makes structures.set()
+    // silently replace the first, which then never renders, bills, or wrecks;
+    // two structures resolving to ONE collateral key make collateralFor bill and
+    // wreck whichever matched first. Both are quiet until a yard has two of the
+    // same thing, which is why they are refused here rather than measured later.
+    const structIds = (site.structures ?? []).map((s) => s.id);
+    const dupStructs = structIds.filter((id, i) => structIds.indexOf(id) !== i);
+    if (dupStructs.length) {
+      bad.push(`duplicate structure ids: ${[...new Set(dupStructs)].join(', ')}`);
+    }
+    const structKeys = (site.structures ?? [])
+      .filter((s) => s.collateral != null)
+      .map((s) => s.collateralKey ?? s.id);
+    const dupKeys = structKeys.filter((k, i) => structKeys.indexOf(k) !== i);
+    if (dupKeys.length) {
+      bad.push(
+        `two priced structures resolve to one collateral key: ${[...new Set(dupKeys)].join(', ')}`
+        + ' — give each a distinct collateralKey and point its anchors at it',
+      );
+    }
     // Lane D's field. `work` is the MECHANISM, not the anchor's type: a post is
     // tensioned from a cleat at its base and a tree strop is thrown, but a
     // bracket bolted up a bare wall is the one you cannot fake — so that, and
@@ -542,6 +563,11 @@ export function createWorld(scene, opts = {}) {
         makeStaticAnchor(a.id, a.type ?? 'post', new THREE.Vector3(st.x, heightAt(st.x, st.z) + 2.4, st.z)),
         { work: a.work },
         a.node ? null : factoryExtras(a.type ?? 'post'),
+        // SPRINT18 gate 5 (E specified, A blessed): the site names its own
+        // collateral target, applied AFTER factoryExtras so the override wins.
+        // Without it, two same-type structures share one baked key and
+        // collateralFor bills or wrecks whichever matched first.
+        a.collateral ? { collateral: a.collateral } : null,
       ));
     }
   }
@@ -687,7 +713,10 @@ export function createWorld(scene, opts = {}) {
       if (!node || !anchor) return false;
       anchor.pos.setFromMatrixPosition(node.matrixWorld);
       anchor.ratingHint = node.userData?.rating_hint ?? 1;
-      anchor.collateral = node.userData?.collateral ?? null;
+      // SPRINT18 gate 5: the bake is the DEFAULT, never a clobber — a site that
+      // named its own target above keeps it. With no override the chain is
+      // identical, so every shipped site is byte-unchanged.
+      anchor.collateral = anchor.collateral ?? node.userData?.collateral ?? null;
       // SPRINT14, E's gap 1: some baked anchor nodes are NOT tie-offs — a door
       // step, a bench top, a broom grip, a lighting hint. They carry no
       // `rating_hint`, and `?? 1` therefore rated them PERFECT: name one in a