diff --git a/mindspace-public-finish-sync.mjs b/mindspace-public-finish-sync.mjs
index d0d970b..d9792d8 100644
--- a/mindspace-public-finish-sync.mjs
+++ b/mindspace-public-finish-sync.mjs
@@ -3,6 +3,7 @@ import path from 'node:path';
 
 import { extractStaticPageLinks } from './mindspace-chat-save.mjs';
 import { DOWNLOADABLE_FILE_PATTERN } from './mindspace-html-download-links.mjs';
+import { scheduleWorkspaceHtmlThumbnailSidecars } from './mindspace-workspace-thumbnails.mjs';
 
 /**
  * Public HTML finish-sync invariants (regression guard — do not simplify away).
@@ -398,6 +399,7 @@ export function materializeMissingPublicHtmlWrites({ messages, publishDir }) {
       fs.mkdirSync(path.dirname(destination), { recursive: true });
       fs.writeFileSync(destination, artifact.content, 'utf8');
       materialized.push(artifact.relativePath);
+      scheduleWorkspaceHtmlThumbnailSidecars(root, artifact.relativePath);
     } catch {
       skipped.push(artifact.relativePath);
     }
diff --git a/mindspace-public-route.mjs b/mindspace-public-route.mjs
index 7025b55..4be24d4 100644
--- a/mindspace-public-route.mjs
+++ b/mindspace-public-route.mjs
@@ -191,6 +191,20 @@ export async function resolveMindSpacePublicRequest({
       };
     }
 
+    // og:image points at <base>.thumbnail.png while only the SVG sidecar may exist on disk.
+    // Serve resolves lazily via ensureThumbnailPng in the MindSpace public file handler.
+    if (/\.thumbnail\.png$/i.test(resolvedPath)) {
+      const svgSibling = resolvedPath.replace(/\.png$/i, '.svg');
+      if (fs.existsSync(svgSibling)) {
+        return {
+          action: 'serve',
+          filePath: resolvedPath,
+          ownerKey,
+          targetDir,
+        };
+      }
+    }
+
     return { action: 'not_found', reason: 'missing_file', ownerKey };
   }
 
diff --git a/mindspace-public-route.test.mjs b/mindspace-public-route.test.mjs
index af1f143..05853aa 100644
--- a/mindspace-public-route.test.mjs
+++ b/mindspace-public-route.test.mjs
@@ -120,3 +120,30 @@ test('resolveMindSpacePublicRequest coordinates canonical redirect, serve, and n
     ownerKey,
   });
 });
+
+test('resolveMindSpacePublicRequest serves missing thumbnail png when svg sidecar exists', async () => {
+  const root = fs.mkdtempSync(path.join(os.tmpdir(), 'ms-public-thumb-'));
+  const ownerKey = '123e4567-e89b-12d3-a456-426614174000';
+  const targetDir = path.join(root, 'MindSpace', ownerKey);
+  const publicDir = path.join(targetDir, 'public');
+  fs.mkdirSync(publicDir, { recursive: true });
+  fs.writeFileSync(path.join(publicDir, 'report.thumbnail.svg'), '<svg xmlns="http://www.w3.org/2000/svg"></svg>');
+
+  const served = await resolveMindSpacePublicRequest({
+    h5Root: root,
+    requestPath: `/${ownerKey}/public/report.thumbnail.png`,
+  });
+  assert.equal(served.action, 'serve');
+  assert.equal(served.filePath, path.join(publicDir, 'report.thumbnail.png'));
+  assert.equal(fs.existsSync(served.filePath), false);
+
+  const stillMissing = await resolveMindSpacePublicRequest({
+    h5Root: root,
+    requestPath: `/${ownerKey}/public/missing.thumbnail.png`,
+  });
+  assert.deepEqual(stillMissing, {
+    action: 'not_found',
+    reason: 'missing_file',
+    ownerKey,
+  });
+});
diff --git a/mindspace-workspace-thumbnails.mjs b/mindspace-workspace-thumbnails.mjs
index 25abd75..59bc396 100644
--- a/mindspace-workspace-thumbnails.mjs
+++ b/mindspace-workspace-thumbnails.mjs
@@ -1,6 +1,7 @@
 import fs from 'node:fs';
 import fsPromises from 'node:fs/promises';
 import path from 'node:path';
+import { ensureThumbnailPng } from './mindspace-thumbnail-png.mjs';
 import { ensureHtmlThumbnail } from './mindspace-thumbnails.mjs';
 
 export function workspaceThumbnailRelativePath(htmlRelativePath) {
@@ -15,14 +16,34 @@ export function workspaceThumbnailAbsolutePath(publishDir, htmlRelativePath) {
   return path.join(publishDir, workspaceThumbnailRelativePath(htmlRelativePath));
 }
 
+function scheduleWorkspaceThumbnailPng(publishDir, htmlRelativePath) {
+  queueMicrotask(() => {
+    void Promise.resolve()
+      .then(() => {
+        const svgPath = workspaceThumbnailAbsolutePath(publishDir, htmlRelativePath);
+        if (fs.existsSync(svgPath)) ensureThumbnailPng(svgPath);
+      })
+      .catch(() => {});
+  });
+}
+
+/** Fire-and-forget SVG + PNG sidecars after public HTML is written (must not block Finish/chat). */
+export function scheduleWorkspaceHtmlThumbnailSidecars(publishDir, htmlRelativePath) {
+  queueMicrotask(() => {
+    void ensureWorkspaceHtmlThumbnail(publishDir, htmlRelativePath).catch(() => {});
+  });
+}
+
 export async function ensureWorkspaceHtmlThumbnail(publishDir, htmlRelativePath, html, meta = {}) {
   const htmlPath = path.join(publishDir, htmlRelativePath);
   const content = html ?? (await fsPromises.readFile(htmlPath, 'utf8'));
   const thumbRel = workspaceThumbnailRelativePath(htmlRelativePath);
-  return ensureHtmlThumbnail(publishDir, thumbRel, content, {
+  const svg = await ensureHtmlThumbnail(publishDir, thumbRel, content, {
     ...meta,
     contentBaseDir: path.dirname(htmlPath),
   });
+  scheduleWorkspaceThumbnailPng(publishDir, htmlRelativePath);
+  return svg;
 }
 
 export async function readWorkspaceThumbnailIfExists(publishDir, htmlRelativePath) {
diff --git a/mindspace-workspace-thumbnails.test.mjs b/mindspace-workspace-thumbnails.test.mjs
index 7cd0b99..efbd417 100644
--- a/mindspace-workspace-thumbnails.test.mjs
+++ b/mindspace-workspace-thumbnails.test.mjs
@@ -27,3 +27,16 @@ test('ensureWorkspaceHtmlThumbnail writes sidecar on html save', async () => {
   assert.match(svg, /运动|普拉提618/i);
   await fs.access(path.join(root, 'pilates.thumbnail.svg'));
 });
+
+test('ensureWorkspaceHtmlThumbnail schedules raster png sidecar', async () => {
+  const root = await fs.mkdtemp(path.join(os.tmpdir(), 'workspace-thumb-png-'));
+  const html = `<!doctype html><html><head>
+    <title>PNG sidecar</title>
+    <meta name="mindspace-cover" content='{"tag":"测试","accent":"#eeb04e","accent2":"#1a0a2e","subtitle":"副标题"}' />
+    </head><body></body></html>`;
+  await fs.writeFile(path.join(root, 'demo.html'), html, 'utf8');
+  await ensureWorkspaceHtmlThumbnail(root, 'demo.html', html, { title: 'PNG sidecar' });
+  await new Promise((resolve) => queueMicrotask(resolve));
+  await new Promise((resolve) => setImmediate(resolve));
+  await fs.access(path.join(root, 'demo.thumbnail.png'));
+});