test: measure runtime reflow at a fixed zoom above the LOD threshold

Fit-to-view on this workflow lands at ~0.52 zoom, below the LOD threshold
(~0.57 at DPR 1) where nodes render as canvas boxes and no Vue components
mount, so the fixture's visibility assertion had nothing to find. Center
the node under test at a deterministic 0.8 zoom instead.

Author: benjcooley

browser_tests/fixtures/utils/runtimeReflow.ts

@@ -23,14 +23,51 @@ interface ReflowNodeUnderTest {
 }
 
 /**
- * Adds a reflow node, fits it into view, and captures its starting height so a
- * test can assert on the height delta after triggering runtime growth.
+ * Zoom at which the node under test is measured. Must sit above the LOD
+ * threshold (~0.57 at DPR 1): below it nodes render as canvas boxes with no
+ * Vue components mounted, and this test's subject is DOM reflow.
+ */
+const MEASUREMENT_ZOOM = 0.8
+
+/** Centers the viewport on a node at a fixed, LOD-safe zoom. */
+async function centerOnNode(comfyPage: ComfyPage, nodeId: string) {
+  await comfyPage.page.evaluate(
+    ([id, zoom]) => {
+      const canvas = window.app!.canvas
+      const graph = window.graph as unknown as TestGraphAccess
+      const node = graph._nodes_by_id[id]
+      if (!node) return
+
+      const element = canvas.canvas
+      canvas.ds.scale = Number(zoom)
+      canvas.ds.offset[0] =
+        -(node.pos[0] + node.size[0] / 2) +
+        element.clientWidth / 2 / Number(zoom)
+      canvas.ds.offset[1] =
+        -(node.pos[1] + node.size[1] / 2) +
+        element.clientHeight / 2 / Number(zoom)
+      canvas.setDirty(true, true)
+    },
+    [nodeId, MEASUREMENT_ZOOM] as const
+  )
+  await comfyPage.nextFrame()
+}
+
+/**
+ * Adds a reflow node, centers it at a deterministic zoom, and captures its
+ * starting height so a test can assert on the height delta after triggering
+ * runtime growth.
+ *
+ * Fit-to-view alone can land below the LOD threshold on this workflow, where
+ * no Vue node elements exist at all, so the node is centered at a fixed zoom
+ * instead of measured wherever fit happens to leave it.
  */
 export async function addReflowNodeAndMeasure(
   comfyPage: ComfyPage
 ): Promise<ReflowNodeUnderTest> {
   const nodeId = await addRuntimeReflowNode(comfyPage)
   await fitToViewInstant(comfyPage)
+  await centerOnNode(comfyPage, nodeId)
 
   const node = comfyPage.vueNodes.getNodeLocator(nodeId)
   await expect(node).toBeVisible()