diff --git a/scripts/lib/deploy-smoke-client.mjs b/scripts/lib/deploy-smoke-client.mjs
index 4ec349f..4157d6e 100644
--- a/scripts/lib/deploy-smoke-client.mjs
+++ b/scripts/lib/deploy-smoke-client.mjs
@@ -14,6 +14,8 @@
 // Output is one line per check; any failed check exits non-zero. Nothing printed carries a
 // credential, cookie, signed URL, or response body beyond the fixed shapes asserted here.
 
+import { connect as connectHttp2 } from "node:http2";
+
 const mode = process.argv[2];
 const apiOrigin = `https://${required("SMOKE_HOSTNAME")}`;
 const dashboardOrigin = process.env.SMOKE_DASHBOARD_HOSTNAME
@@ -192,6 +194,46 @@ async function splitCorsChecks() {
   );
 }
 
+/**
+ * One GET over a real HTTP/2 connection. Node's fetch speaks HTTP/1.1, and the failure this guards
+ * against exists only on HTTP/2: a reset stream, which a browser reports as ERR_HTTP2_PROTOCOL_ERROR.
+ */
+function http2Get(url, headers = {}) {
+  return new Promise((resolve) => {
+    const session = connectHttp2(url.origin);
+    const finish = (result) => {
+      clearTimeout(timer);
+      session.close();
+      resolve(result);
+    };
+    const timer = setTimeout(() => finish({ error: "timeout" }), 10_000);
+    session.on("error", () => finish({ error: "session" }));
+    const stream = session.request({
+      ":method": "GET",
+      ":path": `${url.pathname}${url.search}`,
+      ...headers,
+    });
+    let status;
+    let responseHeaders = {};
+    let bytes = 0;
+    stream.on("response", (received) => {
+      status = received[":status"];
+      responseHeaders = received;
+    });
+    stream.on("data", (chunk) => {
+      bytes += chunk.length;
+    });
+    stream.on("error", (error) => finish({ error: error.code ?? "stream" }));
+    stream.on("end", () => finish({ bytes, headers: responseHeaders, status }));
+    stream.end();
+  });
+}
+
+/** The CORS headers of a response, by name: what a browser would act on. */
+function corsOf(response) {
+  return [...response.headers.keys()].filter((name) => name.startsWith("access-control-"));
+}
+
 async function storageDeliveryCheck() {
   // Core's own provider, from the image, exactly as the API composes it: it reaches object-storage
   // over HTTPS on the private network and signs read URLs for the storage hostname.
@@ -238,6 +280,79 @@ async function storageDeliveryCheck() {
       "a delivered object is Cache-Control: private",
     );
     await provider.delete(bucket, "smoke/object.txt");
+
+    // The same image, twice, over HTTP/2: a browser's second load of a signed URL it has cached is a
+    // conditional request, and must come back as a clean 304, not a reset stream.
+    const png = Buffer.from(
+      "iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAADUlEQVR42mP8z8BQDwAEhQGAhKmMIQAAAABJRU5ErkJggg==",
+      "base64",
+    );
+    await provider.put(bucket, "smoke/image.png", png, {
+      contentLength: png.byteLength,
+      contentType: "image/png",
+    });
+    const image = new URL(
+      (await provider.createReadUrl(bucket, "smoke/image.png", { expiresInSeconds: 300 })).url,
+    );
+    const first = await http2Get(image);
+    check(
+      first.status === 200 && first.bytes === png.byteLength && Boolean(first.headers?.etag),
+      "an image loads over HTTP/2 through the proxy, with a validator (200, ETag)",
+    );
+    const revalidated = await http2Get(image, { "if-none-match": first.headers?.etag ?? "" });
+    check(
+      revalidated.status === 304 && revalidated.error === undefined,
+      `the same image loaded again over HTTP/2 revalidates cleanly (${revalidated.status ?? revalidated.error})`,
+    );
+    const sinceModified = await http2Get(image, {
+      "if-modified-since": first.headers?.["last-modified"] ?? "",
+    });
+    check(
+      sinceModified.status === 304 && sinceModified.error === undefined,
+      `a revalidation by date over HTTP/2 is a clean 304 too (${sinceModified.status ?? sinceModified.error})`,
+    );
+
+    // Delivery-layer CORS is the deployment's own, set by the proxy: exactly the origins whose pages
+    // read objects with fetch(), GET and HEAD only, and nothing of the object store's own answer.
+    const fromApi = await fetch(image, { headers: { origin: apiOrigin } });
+    check(
+      fromApi.headers.get("access-control-allow-origin") === apiOrigin &&
+        (fromApi.headers.get("vary") ?? "").toLowerCase().includes("origin") &&
+        corsOf(fromApi).length === 1,
+      "a read from the API origin is allowed for exactly that origin, with Vary: Origin and nothing else",
+    );
+    if (split) {
+      const fromDashboard = await fetch(image, { headers: { origin: dashboardOrigin } });
+      check(
+        fromDashboard.headers.get("access-control-allow-origin") === dashboardOrigin,
+        "a read from the Dashboard origin is allowed for exactly that origin",
+      );
+    }
+    const fromElsewhere = await fetch(image, { headers: { origin: untrustedOrigin } });
+    check(
+      fromElsewhere.status === 200 && corsOf(fromElsewhere).length === 0,
+      "a read from any other origin gets no CORS header at all",
+    );
+    const preflight = await fetch(image, {
+      headers: { "access-control-request-method": "GET", origin: apiOrigin },
+      method: "OPTIONS",
+    });
+    check(
+      preflight.status === 204 &&
+        preflight.headers.get("access-control-allow-origin") === apiOrigin &&
+        preflight.headers.get("access-control-allow-methods") === "GET, HEAD" &&
+        preflight.headers.get("x-amz-request-id") === null,
+      "the proxy answers a preflight itself (204, GET and HEAD only), never the object store",
+    );
+    const foreignPreflight = await fetch(image, {
+      headers: { "access-control-request-method": "GET", origin: untrustedOrigin },
+      method: "OPTIONS",
+    });
+    check(
+      foreignPreflight.status === 204 && corsOf(foreignPreflight).length === 0,
+      "a preflight from any other origin is answered without permission",
+    );
+    await provider.delete(bucket, "smoke/image.png");
   } finally {
     await provider.close();
   }