diff --git a/bun.lock b/bun.lock
index becaf248..abb7dabe 100644
--- a/bun.lock
+++ b/bun.lock
@@ -235,7 +235,7 @@
     },
     "packages/auth": {
       "name": "@wrnexus/auth",
-      "version": "0.8.24",
+      "version": "0.8.25",
       "dependencies": {
         "@wrnexus/authz": "workspace:*",
         "@wrnexus/captcha": "workspace:*",
diff --git a/packages/auth/assets/client/auth.js b/packages/auth/assets/client/auth.js
index 0643987e..c03d9dd0 100644
--- a/packages/auth/assets/client/auth.js
+++ b/packages/auth/assets/client/auth.js
@@ -137,10 +137,15 @@
     element.dispatchEvent(new CustomEvent(name, { bubbles: true, detail }));
   }
 
-  function navigate(target) {
+  function navigate(target, allowCrossOrigin = false) {
     if (!target) return false;
     const url = new URL(target, location.href);
-    if (url.origin !== location.origin) return false;
+    if (!["http:", "https:"].includes(url.protocol) || url.username || url.password) return false;
+    if (url.origin !== location.origin) {
+      if (!allowCrossOrigin) return false;
+      location.assign(url.href);
+      return true;
+    }
     if (window.__wrnexusNavigate) {
       window.__wrnexusNavigate(url.pathname + url.search + url.hash);
     } else {
@@ -262,6 +267,9 @@
       );
       setState(element, "success", element.dataset.successMessage || "Signed in.");
       dispatch(element, "auth:passkey-authenticated", result);
+      // The same-origin verification endpoint resolves and validates the final
+      // destination, including cross-app SSO handoffs. Never SPA-route those.
+      if (typeof result.redirect === "string" && navigate(result.redirect, true)) return;
       if (element.dataset.redirect) navigate(element.dataset.redirect);
     } catch (error) {
       if (error && error.name === "AbortError") return;
diff --git a/packages/auth/package.json b/packages/auth/package.json
index 45f9f668..7095b9e8 100644
--- a/packages/auth/package.json
+++ b/packages/auth/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@wrnexus/auth",
-  "version": "0.8.24",
+  "version": "0.8.25",
   "description": "Complete authentication, account security, MFA, passkeys, recovery, devices, risk, and audit system for WRNexusJS.",
   "type": "module",
   "sideEffects": false,
diff --git a/packages/auth/test/components.test.ts b/packages/auth/test/components.test.ts
index 638cc377..3345114e 100644
--- a/packages/auth/test/components.test.ts
+++ b/packages/auth/test/components.test.ts
@@ -114,8 +114,9 @@ test("verification components can resend without application-owned schema files"
   }
 });
 
-test("auth browser runtime refuses cross-origin navigation targets", () => {
+test("auth browser runtime refuses cross-origin navigation unless explicitly server-approved", () => {
   const source = readFileSync(join(directory, "..", "assets", "client", "auth.js"), "utf8");
-  expect(source).toContain("if (url.origin !== location.origin) return false");
+  expect(source).toContain("function navigate(target, allowCrossOrigin = false)");
+  expect(source).toContain("if (!allowCrossOrigin) return false");
   expect(source).toContain("!window.AbortController");
 });
diff --git a/packages/auth/test/passkey-runtime.test.ts b/packages/auth/test/passkey-runtime.test.ts
new file mode 100644
index 00000000..412a18d9
--- /dev/null
+++ b/packages/auth/test/passkey-runtime.test.ts
@@ -0,0 +1,48 @@
+import { expect, test, spyOn } from "bun:test";
+import { readFileSync } from "node:fs";
+import { Window } from "happy-dom";
+
+test("passkey sign-in follows the server handoff, including cross-app destinations", async () => {
+  for (const redirect of [
+    "https://account.example.test/?sso_code=synthetic-code",
+    "/signed-in",
+    "javascript:alert(1)",
+  ]) {
+    const window = new Window({ url: "https://sso.example.test/login" });
+    const assign = spyOn(window.location, "assign").mockImplementation(() => {});
+    try {
+      window.document.body.innerHTML = `<div data-auth-passkey><button>Sign in</button><p data-auth-status></p></div>`;
+      Object.defineProperty(window, "PublicKeyCredential", { value: class {} });
+      Object.defineProperty(window.navigator, "credentials", {
+        value: {
+          get: async () => ({
+            id: "synthetic-credential",
+            type: "public-key",
+            rawId: new Uint8Array([1]),
+            response: {
+              clientDataJSON: new Uint8Array([1]),
+              authenticatorData: new Uint8Array([2]),
+              signature: new Uint8Array([3]),
+            },
+          }),
+        },
+      });
+      window.fetch = (async (url: string) =>
+        Response.json(
+          url.endsWith("/options")
+            ? { ok: true, key: "test-key", options: { challenge: "AQID" } }
+            : { ok: true, redirect },
+        )) as any;
+      window.eval(readFileSync(new URL("../assets/client/auth.js", import.meta.url), "utf8"));
+      await (window as any).WRNexusAuth.authenticatePasskey(window.document.querySelector("div"));
+      if (redirect.startsWith("javascript:")) {
+        expect(assign).not.toHaveBeenCalled();
+      } else {
+        expect(assign).toHaveBeenCalledWith(new URL(redirect, window.location.href).href);
+      }
+    } finally {
+      assign.mockRestore();
+      await window.happyDOM.close();
+    }
+  }
+});