diff --git a/scripts/smoke-production.mjs b/scripts/smoke-production.mjs
index 4138cdc..d051265 100644
--- a/scripts/smoke-production.mjs
+++ b/scripts/smoke-production.mjs
@@ -1,5 +1,6 @@
 #!/usr/bin/env node
 import { pathToFileURL } from 'node:url';
+import { PERFORMANCE_BUDGETS } from './lib/bundle-budgets.mjs';
 
 const sha256Pattern = /^[a-f0-9]{64}$/u;
 const privateIdentifiers = /(?:simpastil|simpasteel|neon[ -]?debugger|yourhealth)/iu;
@@ -144,6 +145,56 @@ async function request(fetchImpl, url, init = {}) {
   return response;
 }
 
+async function cancelResponseBody(response) {
+  try { await response.body?.cancel(); } catch { /* Preserve the validation error that required cancellation. */ }
+}
+
+async function countBoundedResponseBody(response, label, maxBytes) {
+  const contentLengthHeader = response.headers.get('content-length');
+  let declaredBytes = null;
+  if (contentLengthHeader !== null) {
+    if (!/^(?:0|[1-9][0-9]*)$/u.test(contentLengthHeader)) {
+      await cancelResponseBody(response);
+      throw new Error(`${label} content-length is malformed.`);
+    }
+    declaredBytes = Number(contentLengthHeader);
+    if (!Number.isSafeInteger(declaredBytes)) {
+      await cancelResponseBody(response);
+      throw new Error(`${label} content-length is outside the safe integer range.`);
+    }
+    if (declaredBytes === 0) {
+      await cancelResponseBody(response);
+      throw new Error(`${label} response is empty.`);
+    }
+    if (declaredBytes > maxBytes) {
+      await cancelResponseBody(response);
+      throw new Error(`${label} exceeds the ${maxBytes}-byte project-still limit.`);
+    }
+  }
+  if (response.body === null) throw new Error(`${label} response body is missing.`);
+
+  const reader = response.body.getReader();
+  let receivedBytes = 0;
+  try {
+    while (true) {
+      const { done, value } = await reader.read();
+      if (done) break;
+      receivedBytes += value.byteLength;
+      if (receivedBytes > maxBytes) {
+        try { await reader.cancel(); } catch { /* Preserve the byte-limit validation error. */ }
+        throw new Error(`${label} exceeds the ${maxBytes}-byte project-still limit.`);
+      }
+    }
+  } finally {
+    reader.releaseLock();
+  }
+  if (receivedBytes === 0) throw new Error(`${label} response is empty.`);
+  if (declaredBytes !== null && receivedBytes !== declaredBytes) {
+    throw new Error(`${label} content-length does not match the streamed byte count.`);
+  }
+  return receivedBytes;
+}
+
 export async function verifyProductionSmoke(options) {
   const canonical = rootHttpsUrl(options.canonicalUrl, 'Canonical URL');
   if (!sha256Pattern.test(options.expectedManifestDigest)) throw new Error('Expected signed manifest digest must be lowercase SHA-256.');
@@ -182,7 +233,11 @@ export async function verifyProductionSmoke(options) {
   if (socialImageType === null || !new RegExp(`^${publicMetadata.socialImageType}(?:;|$)`, 'u').test(socialImageType)) {
     throw new Error('Production social image content-type is missing or unsupported.');
   }
-  if ((await socialImageResponse.arrayBuffer()).byteLength === 0) throw new Error('Production social image response is empty.');
+  await countBoundedResponseBody(
+    socialImageResponse,
+    'Production social image',
+    PERFORMANCE_BUDGETS.projectStill,
+  );
   for (const path of ['/robots.txt', '/sitemap.xml']) {
     const response = await request(fetchImpl, new URL(path, canonical));
     if (response.status !== 200) throw new Error(`${path} did not return 200.`);
diff --git a/tests/deployment/seo.spec.ts b/tests/deployment/seo.spec.ts
index cc37943..3dfc67a 100644
--- a/tests/deployment/seo.spec.ts
+++ b/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);
+  });
 });