diff --git a/AGENTS.md b/AGENTS.md
index 1b98d4e..ffc1260 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -191,7 +191,7 @@ src/
 │   ├── routes/       # Route handlers (auth, home, profile, admin, whoami, health)
 │   ├── components/   # HTML rendering functions
 │   ├── handlers/     # Business logic handlers (e.g., logout)
-│   ├── utils/        # Utilities (cookies, redirects, magic link email)
+│   ├── utils/        # Utilities (redirects, magic link email)
 │   ├── db/           # Planner OAuth client seeding
 │   └── demo/         # Demo application showing auth integration
 ├── auth/             # GitHub provider and ID token claim helpers
diff --git a/src/app/handlers/logout.js b/src/app/handlers/logout.js
index 13279d4..42b510d 100644
--- a/src/app/handlers/logout.js
+++ b/src/app/handlers/logout.js
@@ -1,5 +1,4 @@
 import { validateRedirectUrl } from "../utils/redirect.js";
-import { forwardCookies } from "../utils/cookies.js";
 import { getAuthFromContext } from "../utils/auth.js";
 
 /**
@@ -13,14 +12,20 @@ export const logout = async (c) => {
     c.req.query("redirect_url"),
     "/?message=Bye!",
   );
-  const status = await auth.api.signOut({
+  const signOut = await auth.api.signOut({
     headers: c.req.raw.headers,
-    returnHeaders: true,
+    asResponse: true,
   });
-  // forward headers (cookies)
-  if (status.headers) {
-    forwardCookies(status.headers, c);
+  // asResponse turns APIErrors into error responses; other errors still throw.
+  if (!signOut.ok) {
+    console.error(`Logout failed with status ${signOut.status}`);
+    return signOut;
   }
 
-  return c.redirect(callbackURL);
+  const response = c.redirect(callbackURL);
+  for (const cookie of signOut.headers.getSetCookie()) {
+    response.headers.append("Set-Cookie", cookie);
+  }
+
+  return response;
 };
diff --git a/src/app/utils/cookies.js b/src/app/utils/cookies.js
deleted file mode 100644
index cc64a8e..0000000
--- a/src/app/utils/cookies.js
+++ /dev/null
@@ -1,7 +0,0 @@
-// Helper function to forward Set-Cookie headers from better-auth response
-export const forwardCookies = (headers, c) => {
-  const setCookieHeaders = headers.getSetCookie?.() || [];
-  setCookieHeaders.forEach((cookie) => {
-    c.header("Set-Cookie", cookie);
-  });
-};
diff --git a/test/helpers/test-instance.js b/test/helpers/test-instance.js
index 90aeb97..fe5b9f2 100644
--- a/test/helpers/test-instance.js
+++ b/test/helpers/test-instance.js
@@ -178,49 +178,9 @@ function createTestClient(pool) {
  */
 function createGetAuthHeaders(auth, magicLinksStore) {
   return async function getAuthHeaders(email) {
-    // Send magic link
-    await auth.api.signInMagicLink({
-      body: {
-        email,
-        callbackURL: "http://localhost:3000/profile",
-      },
-      headers: new Headers(),
-    });
-
-    // Get the magic link from the test array
-    const magicLink = magicLinksStore.find((link) => link.email === email);
-
-    if (!magicLink) {
-      throw new Error(`No magic link found for ${email}`);
-    }
-
-    // Verify the magic link to get a session
-    let result;
-    try {
-      result = await auth.api.magicLinkVerify({
-        query: {
-          token: magicLink.token,
-          callbackURL: "http://localhost:3000/profile",
-        },
-        headers: new Headers(),
-        returnHeaders: true,
-      });
-    } catch (error) {
-      // magicLinkVerify may throw an APIError with the redirect response
-      const cookieFromError = extractCookieFromError(error);
-      if (cookieFromError) {
-        return cookieFromError;
-      }
-      throw new Error(`Magic link verification failed: ${error.message}`, {
-        cause: error,
-      });
-    }
-
-    if (!result.headers) {
-      throw new Error("No headers returned from magic link verification");
-    }
+    const headers = await magicLinkVerifyHeaders(auth, magicLinksStore, email);
+    const setCookie = setCookieHeader(headers);
 
-    const setCookie = result.headers.get("set-cookie");
     if (!setCookie) {
       throw new Error("No session cookie in magic link verification response");
     }
@@ -230,31 +190,64 @@ function createGetAuthHeaders(auth, magicLinksStore) {
 }
 
 /**
- * Extract session cookie from a 302 redirect error response
- * @param {Error} error - The error thrown by magicLinkVerify
- * @returns {{cookie: string}|null} Session cookie object or null if not found
+ * Verify a magic link and return the headers carrying the session cookie.
+ *
+ * Better Auth returns those headers as a Headers object on success and may
+ * throw an APIError with them as an array of pairs on the redirect path.
+ * Both shapes reach this function until the API stabilises.
+ * @param {Object} auth - Better Auth instance
+ * @param {Array} magicLinksStore - Array storing captured magic links
+ * @param {string} email - Address to sign in
+ * @returns {Headers|Array} Response headers
  */
-function extractCookieFromError(error) {
-  if (error.statusCode !== 302) {
-    return null;
-  }
+export async function magicLinkVerifyHeaders(auth, magicLinksStore, email) {
+  const callbackURL = "http://localhost:3000/profile";
+  await auth.api.signInMagicLink({
+    body: { email, callbackURL },
+    headers: new Headers(),
+  });
+
+  const magicLink = magicLinksStore.find((link) => link.email === email);
 
-  // ponytail: Better Auth returns headers in two shapes (Headers object vs
-  // array) depending on the error path. Handle both until the API stabilises.
-  let setCookie;
-  if (error.headers && typeof error.headers.get === "function") {
-    setCookie = error.headers.get("set-cookie");
-  } else if (error.headers && Array.isArray(error.headers)) {
-    const setCookieHeader = error.headers.find(
-      (h) => h[0].toLowerCase() === "set-cookie",
-    );
-    setCookie = setCookieHeader ? setCookieHeader[1] : null;
+  if (!magicLink) {
+    throw new Error(`No magic link found for ${email}`);
   }
 
-  if (setCookie) {
-    return parseSessionCookie(setCookie);
+  try {
+    const result = await auth.api.magicLinkVerify({
+      query: { token: magicLink.token, callbackURL },
+      headers: new Headers(),
+      returnHeaders: true,
+    });
+
+    if (!result.headers) {
+      throw new Error("No headers returned from magic link verification");
+    }
+
+    return result.headers;
+  } catch (error) {
+    if (error.statusCode !== 302) throw error;
+    if (!error.headers) {
+      throw new Error("magicLinkVerify redirected without headers", {
+        cause: error,
+      });
+    }
+    return error.headers;
   }
+}
 
+/**
+ * Read the set-cookie header from either shape Better Auth returns
+ * @param {Headers|Array} headers - Response headers
+ * @returns {string|null} The set-cookie header value
+ */
+function setCookieHeader(headers) {
+  if (!headers) return null;
+  if (typeof headers.get === "function") return headers.get("set-cookie");
+  if (Array.isArray(headers)) {
+    const found = headers.find(([name]) => name.toLowerCase() === "set-cookie");
+    return found ? found[1] : null;
+  }
   return null;
 }
 
diff --git a/test/integration/cookie-attributes.test.js b/test/integration/cookie-attributes.test.js
new file mode 100644
index 0000000..ce3b728
--- /dev/null
+++ b/test/integration/cookie-attributes.test.js
@@ -0,0 +1,170 @@
+import { test } from "tap";
+import {
+  getTestInstance,
+  magicLinkVerifyHeaders,
+} from "../helpers/test-instance.js";
+import { createApp } from "../../src/app/app.js";
+import { authorizeParams } from "../helpers/oauth-flow.js";
+
+const SESSION_COOKIE = "better-auth.session_token";
+
+const LOGOUT_COOKIES = [
+  "better-auth.dont_remember",
+  "better-auth.session_data",
+  "better-auth.session_token",
+];
+
+function readSetCookie(headers) {
+  if (!headers) return [];
+  if (typeof headers.getSetCookie === "function") return headers.getSetCookie();
+  if (typeof headers.get === "function") {
+    const value = headers.get("set-cookie");
+    return value ? [value] : [];
+  }
+  if (Array.isArray(headers)) {
+    return headers
+      .filter(([name]) => name.toLowerCase() === "set-cookie")
+      .map(([, value]) => value);
+  }
+  return [];
+}
+
+function cookieNamed(headers, name) {
+  return readSetCookie(headers).find((cookie) => cookie.startsWith(`${name}=`));
+}
+
+function attributes(cookie) {
+  return cookie
+    .split(";")
+    .slice(1)
+    .map((part) => part.trim());
+}
+
+function attributeValue(cookie, name) {
+  const part = attributes(cookie).find(
+    (attribute) => attribute.split("=")[0].toLowerCase() === name.toLowerCase(),
+  );
+  return part?.split("=").slice(1).join("=");
+}
+
+function hasLifetime(cookie) {
+  return Boolean(
+    attributeValue(cookie, "Max-Age") || attributeValue(cookie, "Expires"),
+  );
+}
+
+test("session cookie keeps its security attributes on magic-link verification", async (t) => {
+  const instance = await getTestInstance(t);
+  const headers = await magicLinkVerifyHeaders(
+    instance.auth,
+    instance.getMagicLinks(),
+    "cookie-attributes@example.com",
+  );
+  const cookie = cookieNamed(headers, SESSION_COOKIE);
+
+  t.ok(cookie, "session cookie is set");
+  t.equal(attributeValue(cookie, "HttpOnly"), "", "HttpOnly is set");
+  t.equal(attributeValue(cookie, "SameSite"), "Lax", "SameSite=Lax is set");
+  t.equal(attributeValue(cookie, "Path"), "/", "Path=/ is set");
+  t.ok(hasLifetime(cookie), "session cookie has a lifetime");
+});
+
+test("authorize response sets no cookie", async (t) => {
+  const instance = await getTestInstance(t);
+  const app = createApp(instance.auth, instance.db);
+  const { cookie: sessionCookie } = await instance.getAuthHeaders(
+    "authorize-cookie@example.com",
+  );
+
+  // OAuth state travels in a signed query string (sig=), not in a cookie.
+  const params = authorizeParams({ state: "authorize-cookie" });
+  const res = await app.request(
+    `/api/auth/oauth2/authorize?${params.toString()}`,
+    { headers: { cookie: sessionCookie } },
+  );
+
+  t.equal(res.status, 302, "authorize redirects to the callback");
+  t.same(readSetCookie(res.headers), [], "no cookie is set");
+});
+
+test("logout clears every better-auth cookie", async (t) => {
+  const instance = await getTestInstance(t);
+  const app = createApp(instance.auth, instance.db);
+  const { cookie: sessionCookie } = await instance.getAuthHeaders(
+    "logout-cookies@example.com",
+  );
+
+  const res = await app.request("/logout", {
+    method: "POST",
+    headers: { cookie: sessionCookie },
+  });
+
+  t.equal(res.status, 302, "redirects after logout");
+  const names = readSetCookie(res.headers)
+    .map((cookie) => cookie.split("=")[0])
+    .sort();
+  t.same(names, LOGOUT_COOKIES, "forwards one clearing cookie per cookie");
+});
+
+test("GET /logout clears every better-auth cookie", async (t) => {
+  const instance = await getTestInstance(t);
+  const app = createApp(instance.auth, instance.db);
+  const { cookie: sessionCookie } = await instance.getAuthHeaders(
+    "logout-get@example.com",
+  );
+
+  const res = await app.request("/logout", {
+    headers: { cookie: sessionCookie },
+  });
+
+  t.equal(res.status, 302, "redirects after logout");
+  const names = readSetCookie(res.headers)
+    .map((cookie) => cookie.split("=")[0])
+    .sort();
+  t.same(names, LOGOUT_COOKIES, "forwards one clearing cookie per cookie");
+});
+
+test("logout clearing cookies keep their attributes", async (t) => {
+  const instance = await getTestInstance(t);
+  const app = createApp(instance.auth, instance.db);
+  const { cookie: sessionCookie } = await instance.getAuthHeaders(
+    "logout-attributes@example.com",
+  );
+
+  const res = await app.request("/logout", {
+    method: "POST",
+    headers: { cookie: sessionCookie },
+  });
+  const cookies = readSetCookie(res.headers);
+
+  t.equal(cookies.length, LOGOUT_COOKIES.length, "every cookie is forwarded");
+  for (const cookie of cookies) {
+    const name = cookie.split("=")[0];
+    t.equal(attributeValue(cookie, "Max-Age"), "0", `${name} expires now`);
+    t.equal(attributeValue(cookie, "Path"), "/", `${name} keeps Path=/`);
+    t.equal(attributeValue(cookie, "HttpOnly"), "", `${name} keeps HttpOnly`);
+    t.equal(
+      attributeValue(cookie, "SameSite"),
+      "Lax",
+      `${name} keeps SameSite=Lax`,
+    );
+  }
+});
+
+test("logout surfaces a failed signOut instead of redirecting", async (t) => {
+  const auth = {
+    api: {
+      getSession: async () => null,
+      signOut: async () =>
+        new Response(JSON.stringify({ message: "signOut failed" }), {
+          status: 500,
+        }),
+    },
+  };
+  const app = createApp(auth, null);
+
+  const res = await app.request("/logout");
+
+  t.equal(res.status, 500, "propagates the signOut status");
+  t.equal(res.headers.get("location"), null, "does not redirect");
+});