diff --git a/test/vitest/vitest.ui-isolated-paths.mjs b/test/vitest/vitest.ui-isolated-paths.mjs
index b06df916b538..5727f47d48d5 100644
--- a/test/vitest/vitest.ui-isolated-paths.mjs
+++ b/test/vitest/vitest.ui-isolated-paths.mjs
@@ -2,6 +2,7 @@
 // Tests in this list depend on module singletons or custom-element registration
 // matching the current registry, so they need a fresh graph in the isolated lane.
 export const uiIsolatedTestFiles = [
+  "ui/src/app/app-host.server-prefs.test.ts",
   "ui/src/app/bootstrap.test.ts",
   "ui/src/app/router-outlet.test.ts",
   "ui/src/components/resizable-divider.test.ts",
diff --git a/ui/src/app/gateway-readiness.test.ts b/ui/src/app/gateway-readiness.test.ts
new file mode 100644
index 000000000000..3deebaf94276
--- /dev/null
+++ b/ui/src/app/gateway-readiness.test.ts
@@ -0,0 +1,149 @@
+import { describe, expect, it, vi } from "vitest";
+import type { GatewayBrowserClient } from "../api/gateway.ts";
+import { waitForGatewayClient } from "./gateway-readiness.ts";
+
+type Gateway = Parameters<typeof waitForGatewayClient>[0];
+type GatewaySnapshot = Gateway["snapshot"];
+
+function createGateway(connected = false) {
+  const client = {} as GatewayBrowserClient;
+  let snapshot = {
+    phase: connected ? "connected" : "connecting",
+    client: connected ? client : null,
+  } as GatewaySnapshot;
+  const listeners = new Set<(next: GatewaySnapshot) => void>();
+  const unsubscribe = vi.fn((listener: (next: GatewaySnapshot) => void) => {
+    listeners.delete(listener);
+  });
+  const subscribe = vi.fn((listener: (next: GatewaySnapshot) => void) => {
+    listeners.add(listener);
+    return () => unsubscribe(listener);
+  });
+  const gateway: Gateway = {
+    get snapshot() {
+      return snapshot;
+    },
+    subscribe,
+  };
+  return {
+    gateway,
+    client,
+    subscribe,
+    unsubscribe,
+    connect: () => {
+      snapshot = { ...snapshot, phase: "connected", client };
+      for (const listener of Array.from(listeners)) {
+        listener(snapshot);
+      }
+    },
+  };
+}
+
+describe("waitForGatewayClient", () => {
+  it("rejects an already-aborted signal before returning a connected client", async () => {
+    const { gateway, subscribe } = createGateway(true);
+    const cancellation = new Error("navigation canceled");
+    const controller = new AbortController();
+    controller.abort(cancellation);
+
+    await expect(waitForGatewayClient(gateway, controller.signal)).rejects.toBe(cancellation);
+    expect(subscribe).not.toHaveBeenCalled();
+  });
+
+  it("rejects an already-aborted signal before subscribing to a disconnected gateway", async () => {
+    const { gateway, subscribe } = createGateway();
+    const controller = new AbortController();
+    controller.abort();
+
+    await expect(waitForGatewayClient(gateway, controller.signal)).rejects.toBe(
+      controller.signal.reason,
+    );
+    expect(subscribe).not.toHaveBeenCalled();
+  });
+
+  it("keeps the existing AbortError contract for a non-error cancellation reason", async () => {
+    const { gateway } = createGateway(true);
+    const controller = new AbortController();
+    controller.abort("navigation canceled");
+
+    await expect(waitForGatewayClient(gateway, controller.signal)).rejects.toMatchObject({
+      name: "AbortError",
+      message: "Gateway wait aborted",
+    });
+  });
+
+  it("returns a connected client without subscribing while its signal remains active", async () => {
+    const { gateway, client, subscribe } = createGateway(true);
+
+    await expect(waitForGatewayClient(gateway, new AbortController().signal)).resolves.toBe(client);
+    expect(subscribe).not.toHaveBeenCalled();
+  });
+
+  it("removes a pending gateway subscription when its signal is aborted", async () => {
+    const { gateway, unsubscribe } = createGateway();
+    const cancellation = new Error("navigation canceled");
+    const controller = new AbortController();
+    const pending = waitForGatewayClient(gateway, controller.signal);
+
+    controller.abort(cancellation);
+
+    await expect(pending).rejects.toBe(cancellation);
+    expect(unsubscribe).toHaveBeenCalledOnce();
+  });
+
+  it("releases a pending subscription once its gateway connects", async () => {
+    const { gateway, client, connect, unsubscribe } = createGateway();
+    const controller = new AbortController();
+    const pending = waitForGatewayClient(gateway, controller.signal);
+
+    connect();
+
+    await expect(pending).resolves.toBe(client);
+    expect(unsubscribe).toHaveBeenCalledOnce();
+    controller.abort();
+    expect(unsubscribe).toHaveBeenCalledOnce();
+  });
+
+  it("does not retain an abort listener after synchronous connection replay", async () => {
+    const client = {} as GatewayBrowserClient;
+    const snapshot = { phase: "connected", client } as GatewaySnapshot;
+    const unsubscribe = vi.fn();
+    const gateway: Gateway = {
+      snapshot: { phase: "connecting", client: null } as GatewaySnapshot,
+      subscribe(listener) {
+        listener(snapshot);
+        return unsubscribe;
+      },
+    };
+    const controller = new AbortController();
+    const addAbortListener = vi.spyOn(controller.signal, "addEventListener");
+    const removeAbortListener = vi.spyOn(controller.signal, "removeEventListener");
+
+    await expect(waitForGatewayClient(gateway, controller.signal)).resolves.toBe(client);
+
+    const abortListener = addAbortListener.mock.calls[0]?.[1];
+    expect(abortListener).toBeTypeOf("function");
+    expect(removeAbortListener).toHaveBeenCalledWith("abort", abortListener);
+    expect(unsubscribe).toHaveBeenCalledOnce();
+
+    controller.abort(new Error("late navigation cancellation"));
+
+    expect(unsubscribe).toHaveBeenCalledOnce();
+  });
+
+  it("releases a subscription when it synchronously aborts during registration", async () => {
+    const cancellation = new Error("navigation canceled during registration");
+    const controller = new AbortController();
+    const unsubscribe = vi.fn();
+    const gateway: Gateway = {
+      snapshot: { phase: "connecting", client: null } as GatewaySnapshot,
+      subscribe() {
+        controller.abort(cancellation);
+        return unsubscribe;
+      },
+    };
+
+    await expect(waitForGatewayClient(gateway, controller.signal)).rejects.toBe(cancellation);
+    expect(unsubscribe).toHaveBeenCalledOnce();
+  });
+});
diff --git a/ui/src/app/gateway-readiness.ts b/ui/src/app/gateway-readiness.ts
index bed6e65ecf5d..3ccdb9269451 100644
--- a/ui/src/app/gateway-readiness.ts
+++ b/ui/src/app/gateway-readiness.ts
@@ -12,12 +12,15 @@ export function waitForGatewayClient(
   signal: AbortSignal,
 ): Promise<GatewayBrowserClient> {
   const current = gateway.snapshot.client;
+  if (signal.aborted) {
+    return Promise.reject(abortError(signal));
+  }
   if (current && gateway.snapshot.phase === "connected") {
     return Promise.resolve(current);
   }
   return new Promise((resolve, reject) => {
     let unsubscribe: () => void = () => undefined;
-    let settled = false;
+    let settled = false; // A synchronous replay must not retain its abort listener.
     const cleanup = () => {
       unsubscribe();
       signal.removeEventListener("abort", onAbort);
@@ -26,6 +29,7 @@ export function waitForGatewayClient(
       cleanup();
       reject(abortError(signal));
     };
+    signal.addEventListener("abort", onAbort, { once: true });
     unsubscribe = gateway.subscribe((snapshot) => {
       if (snapshot.phase === "connected" && snapshot.client) {
         settled = true;
@@ -33,12 +37,8 @@ export function waitForGatewayClient(
         resolve(snapshot.client);
       }
     });
-    if (settled) {
+    if (settled || signal.aborted) {
       unsubscribe();
     }
-    signal.addEventListener("abort", onAbort, { once: true });
-    if (signal.aborted) {
-      onAbort();
-    }
   });
 }