diff --git a/lib/fixtures/twoNodeExpansionFixture.ts b/lib/fixtures/twoNodeExpansionFixture.ts
new file mode 100644
index 0000000..e641d8a
--- /dev/null
+++ b/lib/fixtures/twoNodeExpansionFixture.ts
@@ -0,0 +1,66 @@
+import RBush from "rbush"
+import type {
+  RectDiffExpansionSolverInput,
+  RectDiffExpansionSolverSnapshot,
+} from "../solvers/RectDiffExpansionSolver/RectDiffExpansionSolver"
+import type { SimpleRouteJson } from "../types/srj-types"
+import type { XYRect } from "../rectdiff-types"
+import type { RTreeRect } from "lib/types/capacity-mesh-types"
+
+/**
+ * Builds a minimal RectDiffExpansionSolver snapshot with exactly two nodes
+ * separated by empty space. This keeps the data close to the solver’s real
+ * input shape so we can reuse it for demos/tests that reproduce the gap issue.
+ */
+export const createTwoNodeExpansionInput = (): RectDiffExpansionSolverInput => {
+  const srj: SimpleRouteJson = {
+    bounds: { minX: 0, maxX: 12, minY: 0, maxY: 4 },
+    layerCount: 1,
+    minTraceWidth: 0.2,
+    obstacles: [],
+    connections: [],
+  }
+  const layerCount = srj.layerCount ?? 1
+  const bounds: XYRect = {
+    x: srj.bounds.minX,
+    y: srj.bounds.minY,
+    width: srj.bounds.maxX - srj.bounds.minX,
+    height: srj.bounds.maxY - srj.bounds.minY,
+  }
+
+  const obstacleIndexByLayer = Array.from(
+    { length: layerCount },
+    () => new RBush<RTreeRect>(),
+  )
+  // Start with all-empty obstacle indexes for a "clean" scenario
+
+  const initialSnapshot: RectDiffExpansionSolverSnapshot = {
+    srj,
+    layerNames: ["top"],
+    layerCount,
+    bounds,
+    options: { gridSizes: [1] },
+    boardVoidRects: [],
+    gridIndex: 0,
+    candidates: [],
+    placed: [
+      {
+        rect: { x: 0.5, y: 0.5, width: 2, height: 3 },
+        zLayers: [0],
+      },
+      {
+        rect: { x: 9.5, y: 0.5, width: 2, height: 3 },
+        zLayers: [0],
+      },
+    ],
+    expansionIndex: 0,
+    edgeAnalysisDone: true,
+    totalSeedsThisGrid: 0,
+    consumedSeedsThisGrid: 0,
+  }
+
+  return {
+    initialSnapshot,
+    obstacleIndexByLayer,
+  }
+}
diff --git a/pages/features/should-expand-node.page.tsx b/pages/features/should-expand-node.page.tsx
new file mode 100644
index 0000000..7798ce2
--- /dev/null
+++ b/pages/features/should-expand-node.page.tsx
@@ -0,0 +1,13 @@
+import { useMemo } from "react"
+import { RectDiffExpansionSolver } from "lib/solvers/RectDiffExpansionSolver/RectDiffExpansionSolver"
+import { createTwoNodeExpansionInput } from "lib/fixtures/twoNodeExpansionFixture"
+import { SolverDebugger3d } from "../../components/SolverDebugger3d"
+
+export default () => {
+  const solver = useMemo(
+    () => new RectDiffExpansionSolver(createTwoNodeExpansionInput()),
+    [],
+  )
+
+  return <SolverDebugger3d solver={solver} />
+}
diff --git a/pages/gap-fill-h-shape-should-expand-node.page.tsx b/pages/gap-fill-h-shape-should-expand-node.page.tsx
deleted file mode 100644
index ce84755..0000000
--- a/pages/gap-fill-h-shape-should-expand-node.page.tsx
+++ /dev/null
@@ -1,23 +0,0 @@
-import fixture from "../test-assets/gap-fill-h-shape-should-expand-node.json"
-import { GapFillSolverPipeline } from "../lib/solvers/GapFillSolver/GapFillSolverPipeline"
-import type { CapacityMeshNode } from "../lib/types/capacity-mesh-types"
-import { useMemo } from "react"
-import { SolverDebugger3d } from "../components/SolverDebugger3d"
-
-export default () => {
-  const solver = useMemo(
-    () =>
-      new GapFillSolverPipeline({
-        meshNodes: fixture.meshNodes as CapacityMeshNode[],
-      }),
-    [],
-  )
-
-  return (
-    <SolverDebugger3d
-      solver={solver}
-      defaultShowOutput={true}
-      defaultShowRoot={true}
-    />
-  )
-}
diff --git a/tests/__snapshots__/should-expand-node.snap.svg b/tests/__snapshots__/should-expand-node.snap.svg
index 8282007..5268ba7 100644
--- a/tests/__snapshots__/should-expand-node.snap.svg
+++ b/tests/__snapshots__/should-expand-node.snap.svg
@@ -1,4 +1,4 @@
-<svg width="640" height="480" viewBox="0 0 640 480" xmlns="http://www.w3.org/2000/svg"><rect width="100%" height="100%" fill="white"/><g><rect data-type="rect" data-label="node" data-x="-3" data-y="0" x="86.66666666666666" y="40" width="66.66666666666666" height="400" fill="#dbeafe" stroke="black" stroke-width="0.015"/></g><g><rect data-type="rect" data-label="node" data-x="3" data-y="0" x="486.6666666666667" y="40" width="66.66666666666669" height="400" fill="#dbeafe" stroke="black" stroke-width="0.015"/></g><g><rect data-type="rect" data-label="node" data-x="0" data-y="0" x="253.33333333333331" y="206.66666666666666" width="133.33333333333337" height="66.66666666666666" fill="#dbeafe" stroke="black" stroke-width="0.015"/></g><g><rect data-type="rect" data-label="node" data-x="-1.75" data-y="0" x="153.33333333333331" y="40" width="100" height="400" fill="#dbeafe" stroke="black" stroke-width="0.015"/></g><g><rect data-type="rect" data-label="node" data-x="1.75" data-y="0" x="386.6666666666667" y="40" width="100" height="400" fill="#dbeafe" stroke="black" stroke-width="0.015"/></g><g id="crosshair" style="display: none"><line id="crosshair-h" y1="0" y2="480" stroke="#666" stroke-width="0.5"/><line id="crosshair-v" x1="0" x2="640" stroke="#666" stroke-width="0.5"/><text id="coordinates" font-family="monospace" font-size="12" fill="#666"></text></g><script><![CDATA[
+<svg width="640" height="480" viewBox="0 0 640 480" xmlns="http://www.w3.org/2000/svg"><rect width="100%" height="100%" fill="white"/><g><rect data-type="rect" data-label="node" data-x="1.5" data-y="2" x="40.000000000000014" y="163.63636363636363" width="101.8181818181818" height="152.72727272727275" fill="#dbeafe" stroke="black" stroke-width="0.019642857142857142"/></g><g><rect data-type="rect" data-label="node" data-x="10.5" data-y="2" x="498.1818181818182" y="163.63636363636363" width="101.81818181818181" height="152.72727272727275" fill="#dbeafe" stroke="black" stroke-width="0.019642857142857142"/></g><g id="crosshair" style="display: none"><line id="crosshair-h" y1="0" y2="480" stroke="#666" stroke-width="0.5"/><line id="crosshair-v" x1="0" x2="640" stroke="#666" stroke-width="0.5"/><text id="coordinates" font-family="monospace" font-size="12" fill="#666"></text></g><script><![CDATA[
               document.currentScript.parentElement.addEventListener('mousemove', (e) => {
                 const svg = e.currentTarget;
                 const rect = svg.getBoundingClientRect();
@@ -20,7 +20,7 @@
                 v.setAttribute('y2', '480');
 
                 // Calculate real coordinates using inverse transformation
-                const matrix = {"a":66.66666666666667,"c":0,"e":320,"b":0,"d":-66.66666666666667,"f":240};
+                const matrix = {"a":50.90909090909091,"c":0,"e":14.545454545454561,"b":0,"d":-50.90909090909091,"f":341.8181818181818};
                 // Manually invert and apply the affine transform
                 // Since we only use translate and scale, we can directly compute:
                 // x' = (x - tx) / sx
diff --git a/tests/should-expand-node.test.ts b/tests/should-expand-node.test.ts
index 2e7deab..34fa8d5 100644
--- a/tests/should-expand-node.test.ts
+++ b/tests/should-expand-node.test.ts
@@ -1,24 +1,18 @@
 import { expect, test } from "bun:test"
-import middleGapFixture from "test-assets/gap-fill-h-shape-should-expand-node.json"
 import { getSvgFromGraphicsObject } from "graphics-debug"
-import { GapFillSolverPipeline } from "lib/solvers/GapFillSolver/GapFillSolverPipeline"
-import type { CapacityMeshNode } from "lib/types/capacity-mesh-types"
+import { RectDiffExpansionSolver } from "lib/solvers/RectDiffExpansionSolver/RectDiffExpansionSolver"
+import { createTwoNodeExpansionInput } from "lib/fixtures/twoNodeExpansionFixture"
 import { makeCapacityMeshNodeWithLayerInfo } from "./fixtures/makeCapacityMeshNodeWithLayerInfo"
 
-test("should expand capacityMeshNode to fill the gap", async () => {
-  const solver = new GapFillSolverPipeline({
-    meshNodes: middleGapFixture.meshNodes as CapacityMeshNode[],
-  })
+test("RectDiff expansion reproduces the two-node gap fixture", async () => {
+  const solver = new RectDiffExpansionSolver(createTwoNodeExpansionInput())
 
   solver.solve()
 
-  const { outputNodes } = solver.getOutput()
+  const { meshNodes } = solver.getOutput()
+  expect(meshNodes.length).toBeGreaterThanOrEqual(2)
 
-  expect(outputNodes.length).toBeGreaterThanOrEqual(
-    middleGapFixture.meshNodes.length,
-  )
-
-  const finalGraphics = makeCapacityMeshNodeWithLayerInfo(outputNodes)
+  const finalGraphics = makeCapacityMeshNodeWithLayerInfo(meshNodes)
   const svg = getSvgFromGraphicsObject(
     { rects: finalGraphics.values().toArray().flat() },
     {
@@ -27,8 +21,5 @@ test("should expand capacityMeshNode to fill the gap", async () => {
     },
   )
 
-  // More means we have added new nodes to fill the gap
-  // expect(outputNodes.length).toEqual(3)
-
   await expect(svg).toMatchSvgSnapshot(import.meta.path)
 })