fix: bound social preview smoke response

tests/deployment/seo.spec.ts

@@ -11,6 +11,8 @@ const alternate = 'http://www.portfolio.example/';
 const escapedTitle = 'Luca Pîslaru — System Administrator & Full-Stack Developer';
 const description = 'Portfolio of Luca Pîslaru, a Bucharest-based System Administrator and Full-Stack Developer working across Linux infrastructure and end-to-end software delivery.';
 const socialImage = `${canonical}assets/project-social-preview.webp`;
+const projectStillMaxBytes = 400 * 1024;
+const socialImageFixture = Buffer.alloc(15_068);
 const html = `<!doctype html><html><head>
 <title>${escapedTitle}</title>
 <meta name="description" content="${description}" />
@@ -36,6 +38,8 @@ interface FixtureOptions {
   html?: string;
   imageStatus?: number;
   imageType?: string;
+  imageContentLength?: string | null;
+  imageChunks?: readonly Buffer[];
 }
 
 const mutateJsonLd = (source: string, mutate: (graph: Record<string, any>) => void): string =>
@@ -78,12 +82,19 @@ async function fixtureFetch(options: FixtureOptions = {}) {
     }
     if (url.pathname === '/assets/project-social-preview.webp') {
       const status = options.imageStatus ?? 200;
-      response.writeHead(status, {
+      const chunks = status === 200 ? options.imageChunks ?? [socialImageFixture] : [];
+      const contentLength = options.imageContentLength === undefined
+        ? String(chunks.reduce((total, chunk) => total + chunk.byteLength, 0))
+        : options.imageContentLength;
+      const headers: Record<string, string> = {
         ...base,
         'content-type': options.imageType ?? 'image/webp',
         'cache-control': 'public, max-age=31536000, immutable',
-      });
-      response.end(status === 200 ? Buffer.from('social-preview-fixture') : undefined);
+      };
+      if (contentLength !== null) headers['content-length'] = contentLength;
+      response.writeHead(status, headers);
+      for (const chunk of chunks) response.write(chunk);
+      response.end();
       return;
     }
     if (url.pathname === '/assets/demo.12345678.webm') {
@@ -224,4 +235,36 @@ describe('production smoke and SEO contract', () => {
       fetchImpl,
     })).rejects.toThrow(error);
   });
+
+  it.each([
+    {
+      name: 'a zero-byte body',
+      options: { imageChunks: [], imageContentLength: '0' },
+      error: /social image.*empty|zero-byte/iu,
+    },
+    {
+      name: 'a declared body above the project-still limit',
+      options: {
+        imageChunks: [Buffer.alloc(projectStillMaxBytes + 1)],
+        imageContentLength: String(projectStillMaxBytes + 1),
+      },
+      error: /social image.*(?:limit|large|400)/iu,
+    },
+    {
+      name: 'an undeclared chunked body above the project-still limit',
+      options: {
+        imageChunks: [Buffer.alloc(projectStillMaxBytes), Buffer.alloc(1)],
+        imageContentLength: null,
+      },
+      error: /social image.*(?:limit|large|400)/iu,
+    },
+  ])('rejects $name without buffering the social image', async ({ options, error }) => {
+    const fetchImpl = await fixtureFetch(options);
+
+    await expect(verifyProductionSmoke({
+      canonicalUrl: canonical,
+      expectedManifestDigest: digest,
+      fetchImpl,
+    })).rejects.toThrow(error);
+  });
 });