perf(studio-server): preview steps skip the page parse when a tag scan answers

packages/core/src/compiler/scenePartsManifest.ts

@@ -14,6 +14,7 @@ const hash = (text: string) => createHash("sha1").update(text).digest("hex").sli
  * `ignore` lists selectors for parts that change on every build without changing what is shown.
  */
 export function addScenePartsManifest(html: string, ignore: readonly string[] = []): string {
+  if (!html.includes(SCENE_PART_ATTR)) return html;
   const doc = parseHTMLContent(html);
   const parts = [...doc.querySelectorAll(`[${SCENE_PART_ATTR}]`)];
   if (parts.length === 0) return html;

packages/studio-server/src/helpers/lazyPreviewImages.ts

@@ -15,9 +15,10 @@ const hasLoading = (img: Element) =>
 
 export function lazyPreviewImages(html: string): string {
   if (!/<!doctype|<html[\s>]/i.test(html)) return html;
-  const images = [...parseHTML(html).document.querySelectorAll("img")];
   // The scanner skips comments and raw text, so its `<img` offsets line up with the DOM's images.
   const tags = findStartTags(html, "img");
+  if (tags.length === 0) return html;
+  const images = [...parseHTML(html).document.querySelectorAll("img")];
   if (tags.length !== images.length) return html;
   const parts: string[] = [];
   let from = 0;

packages/studio-server/src/helpers/subComposition.ts

@@ -11,7 +11,7 @@ import {
   RUNTIME_BOOTSTRAP_ATTR,
   stripEmbeddedRuntimeScripts,
 } from "@hyperframes/core/compiler";
-import { isFullHtmlDocument } from "@hyperframes/core/compiler/html-document";
+import { findStartTags, isFullHtmlDocument } from "@hyperframes/core/compiler/html-document";
 import { gsapCdnDist } from "@hyperframes/core/gsap-cdn";
 import { htmlHasGsapCore, insertGsapCoreBeforeHeadPlugin } from "./gsapCoreScript.js";
 import { withRootPathsRelative } from "./rootPaths.js";
@@ -381,5 +381,5 @@ ${rewrittenContent}
 
 /** True for a real `<base>` element; the text "<base" inside a script or comment does not count. */
 export function hasBaseElement(html: string): boolean {
-  return parseHTML(html).document.querySelector("base") !== null;
+  return findStartTags(html, "base").length > 0;
 }

packages/studio-server/src/routes/preview.parseCount.test.ts

@@ -0,0 +1,62 @@
+import { expect, it, vi } from "vitest";
+import { Hono } from "hono";
+import { mkdtempSync, rmSync, writeFileSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import type { StudioApiAdapter } from "../types";
+
+const pageParses = vi.hoisted(() => ({ count: 0, minLength: Infinity }));
+vi.mock("linkedom", async (actual) => {
+  const real = await actual<typeof import("linkedom")>();
+  return {
+    ...real,
+    parseHTML: (html: string, ...rest: unknown[]) => {
+      if (html.length >= pageParses.minLength) pageParses.count += 1;
+      return (real.parseHTML as (...args: unknown[]) => ReturnType<typeof real.parseHTML>)(
+        html,
+        ...rest,
+      );
+    },
+  };
+});
+
+const { registerPreviewRoutes } = await import("./preview");
+
+it("parses a stamped page once per preview build (the read-tracking walk) when it has no images, <base> or scene parts", async () => {
+  const dir = mkdtempSync(join(tmpdir(), "hf-preview-parses-"));
+  try {
+    const shapes = Array.from(
+      { length: 200 },
+      (_, i) => `<path data-hf-id="hf-p${i}" d="M${i} 0h1v1z"/>`,
+    );
+    const page =
+      `<!DOCTYPE html><html><head><meta charset="utf-8"><title>t</title></head><body>` +
+      `<div data-hf-id="hf-root" data-composition-id="main"><svg data-hf-id="hf-svg">${shapes.join("")}</svg></div>` +
+      `</body></html>`;
+    writeFileSync(join(dir, "index.html"), page);
+    const adapter = {
+      listProjects: () => [],
+      resolveProject: async (id: string) => ({ id, dir }),
+      bundle: async () => page,
+      lint: async () => ({ findings: [] }),
+      runtimeUrl: "/api/runtime.js",
+      rendersDir: () => "/tmp/renders",
+      startRender: () => ({
+        id: "job",
+        status: "rendering",
+        progress: 0,
+        outputPath: "/tmp/out.mp4",
+      }),
+    } as unknown as StudioApiAdapter;
+    const app = new Hono();
+    registerPreviewRoutes(app, adapter);
+    pageParses.minLength = page.length / 2;
+
+    const response = await app.request("http://localhost/projects/demo/preview");
+
+    expect(response.status).toBe(200);
+    expect(pageParses.count).toBe(1);
+  } finally {
+    rmSync(dir, { recursive: true, force: true });
+  }
+});