diff --git a/packages/web-shell/client/test/setup.test.ts b/packages/web-shell/client/test/setup.test.ts
new file mode 100644
index 00000000000..ecaddb75552
--- /dev/null
+++ b/packages/web-shell/client/test/setup.test.ts
@@ -0,0 +1,23 @@
+// @vitest-environment jsdom
+
+import { describe, expect, it } from 'vitest';
+
+describe('web-shell test setup', () => {
+  it('provides range layout methods used by CodeMirror', () => {
+    const range = document.createRange();
+
+    expect(typeof range.getClientRects).toBe('function');
+    expect(typeof range.getBoundingClientRect).toBe('function');
+    expect(range.getClientRects()).toHaveLength(0);
+    expect(range.getBoundingClientRect()).toMatchObject({
+      bottom: 0,
+      height: 0,
+      left: 0,
+      right: 0,
+      top: 0,
+      width: 0,
+      x: 0,
+      y: 0,
+    });
+  });
+});
diff --git a/packages/web-shell/client/test/setup.ts b/packages/web-shell/client/test/setup.ts
index 79d2dfd9d7a..ace65e79f56 100644
--- a/packages/web-shell/client/test/setup.ts
+++ b/packages/web-shell/client/test/setup.ts
@@ -6,9 +6,35 @@ import { vi } from 'vitest';
 
 const globalWithDom = globalThis as typeof globalThis & {
   Element?: typeof Element;
+  Range?: typeof Range;
   ResizeObserver?: typeof ResizeObserver;
 };
 
+function createEmptyDOMRect(): DOMRect {
+  if (typeof DOMRect === 'function') {
+    return new DOMRect(0, 0, 0, 0);
+  }
+
+  return {
+    bottom: 0,
+    height: 0,
+    left: 0,
+    right: 0,
+    top: 0,
+    width: 0,
+    x: 0,
+    y: 0,
+    toJSON: () => ({}),
+  } as DOMRect;
+}
+
+function createEmptyDOMRectList(): DOMRectList {
+  return {
+    length: 0,
+    item: () => null,
+  } as DOMRectList;
+}
+
 if (typeof globalWithDom.ResizeObserver === 'undefined') {
   globalWithDom.ResizeObserver = class ResizeObserverStub {
     observe() {}
@@ -24,6 +50,16 @@ if (
   globalWithDom.Element.prototype.scrollIntoView = () => {};
 }
 
+if (typeof globalWithDom.Range !== 'undefined') {
+  const rangePrototype = globalWithDom.Range.prototype as Range & {
+    getBoundingClientRect?: () => DOMRect;
+    getClientRects?: () => DOMRectList;
+  };
+
+  rangePrototype.getBoundingClientRect ??= createEmptyDOMRect;
+  rangePrototype.getClientRects ??= createEmptyDOMRectList;
+}
+
 if (typeof navigator !== 'undefined' && !navigator.clipboard) {
   Object.defineProperty(navigator, 'clipboard', {
     configurable: true,
diff --git a/packages/webui/src/daemon/session/DaemonSessionProvider.test.tsx b/packages/webui/src/daemon/session/DaemonSessionProvider.test.tsx
index 36d24597f30..76db901a4b3 100644
--- a/packages/webui/src/daemon/session/DaemonSessionProvider.test.tsx
+++ b/packages/webui/src/daemon/session/DaemonSessionProvider.test.tsx
@@ -5378,21 +5378,22 @@ describe('DaemonSessionProvider', () => {
       modelServices: [],
       workspaceCwd: '/mock-workspace',
     });
+    const releaseHeartbeatFailure = createDeferred<void>();
     const heartbeat = vi.fn(async () => {
+      await releaseHeartbeatFailure.promise;
       throw Object.assign(new Error('session gone'), { status: 410 });
     });
+    const submitStarted = createDeferred<void>();
     const session = createMockSession({
       heartbeat,
-      submitPrompt: vi.fn(
-        (_req: unknown, signal?: AbortSignal) =>
-          new Promise<NonBlockingPromptAccepted>((_resolve, reject) => {
-            signal?.addEventListener(
-              'abort',
-              () => reject(createAbortError()),
-              { once: true },
-            );
-          }),
-      ),
+      submitPrompt: vi.fn((_req: unknown, signal?: AbortSignal) => {
+        submitStarted.resolve();
+        return new Promise<NonBlockingPromptAccepted>((_resolve, reject) => {
+          signal?.addEventListener('abort', () => reject(createAbortError()), {
+            once: true,
+          });
+        });
+      }),
       events: createIdleEvents(),
     });
     sdkMocks.sessions.push(session);
@@ -5415,10 +5416,12 @@ describe('DaemonSessionProvider', () => {
     let promptResult: Promise<unknown> | undefined;
     await act(async () => {
       promptResult = providerActions.sendPrompt('still running');
+      await submitStarted.promise;
       await flushPromises();
     });
 
     await act(async () => {
+      releaseHeartbeatFailure.resolve();
       await wait(50);
       await flushPromises();
     });