diff --git a/packages/cli/src/gemini.tsx b/packages/cli/src/gemini.tsx
index 2ae7d72d32..06c69bf784 100644
--- a/packages/cli/src/gemini.tsx
+++ b/packages/cli/src/gemini.tsx
@@ -181,6 +181,7 @@ Stack trace:
 ${reason.stack}`
         : ''
     }`;
+    debugLogger.error(errorMessage);
     appEvents.emit(AppEvent.LogError, errorMessage);
     if (!unhandledRejectionOccurred) {
       unhandledRejectionOccurred = true;
diff --git a/packages/cli/src/ui/components/shared/ErrorBoundary.test.tsx b/packages/cli/src/ui/components/shared/ErrorBoundary.test.tsx
index 77371206bd..8576943e75 100644
--- a/packages/cli/src/ui/components/shared/ErrorBoundary.test.tsx
+++ b/packages/cli/src/ui/components/shared/ErrorBoundary.test.tsx
@@ -15,6 +15,11 @@ const Thrower = ({ message }: { message: string }) => {
   throw new Error(message);
 };
 
+// A child that throws a non-Error value (string).
+const StringThrower = ({ message }: { message: string }) => {
+  throw message;
+};
+
 describe('ErrorBoundary', () => {
   // React logs caught render errors to console.error; silence it so the test
   // output stays clean (the boundary catching the error is the point).
@@ -103,4 +108,20 @@ describe('ErrorBoundary', () => {
     rerender(tree);
     expect(lastFrame()).toContain('recovered');
   });
+
+  it('normalizes a non-Error thrown value to an Error instance', () => {
+    const onError = vi.fn();
+    const { lastFrame } = render(
+      <ErrorBoundary onError={onError}>
+        <StringThrower message="string error" />
+      </ErrorBoundary>,
+    );
+    // The fallback renders the stringified value.
+    expect(lastFrame()).toContain('string error');
+    // onError receives a proper Error instance, not the raw string.
+    expect(onError).toHaveBeenCalledTimes(1);
+    const [error] = onError.mock.calls[0];
+    expect(error).toBeInstanceOf(Error);
+    expect((error as Error).message).toBe('string error');
+  });
 });
diff --git a/packages/cli/src/ui/components/shared/ErrorBoundary.tsx b/packages/cli/src/ui/components/shared/ErrorBoundary.tsx
index 37e508ba9b..dec8a68157 100644
--- a/packages/cli/src/ui/components/shared/ErrorBoundary.tsx
+++ b/packages/cli/src/ui/components/shared/ErrorBoundary.tsx
@@ -9,6 +9,13 @@ import { Box, Text } from 'ink';
 import { theme } from '../../semantic-colors.js';
 import { sanitizeTerminalText } from '../../utils/textUtils.js';
 
+function normalizeError(error: unknown): Error {
+  if (error instanceof Error) {
+    return error;
+  }
+  return new Error(String(error));
+}
+
 interface ErrorBoundaryProps {
   children: ReactNode;
   /**
@@ -38,12 +45,12 @@ export class ErrorBoundary extends Component<
 > {
   override state: ErrorBoundaryState = { error: null };
 
-  static getDerivedStateFromError(error: Error): ErrorBoundaryState {
-    return { error };
+  static getDerivedStateFromError(error: unknown): ErrorBoundaryState {
+    return { error: normalizeError(error) };
   }
 
-  override componentDidCatch(error: Error, info: ErrorInfo): void {
-    this.props.onError?.(error, info);
+  override componentDidCatch(error: unknown, info: ErrorInfo): void {
+    this.props.onError?.(normalizeError(error), info);
   }
 
   private readonly reset = () => {
diff --git a/packages/cli/src/ui/startInteractiveUI.tsx b/packages/cli/src/ui/startInteractiveUI.tsx
index ffd1a4f143..1c06c586a1 100644
--- a/packages/cli/src/ui/startInteractiveUI.tsx
+++ b/packages/cli/src/ui/startInteractiveUI.tsx
@@ -33,7 +33,8 @@ import {
 } from './utils/kittyProtocolDetector.js';
 import { installTerminalRedrawOptimizer } from './utils/terminalRedrawOptimizer.js';
 import { installSynchronizedOutput } from './utils/synchronizedOutput.js';
-import { registerCleanup } from '../utils/cleanup.js';
+import { ErrorBoundary } from './components/shared/ErrorBoundary.js';
+import { registerCleanup, runExitCleanup } from '../utils/cleanup.js';
 import { stopAndGetCapturedInput } from '../utils/earlyInputCapture.js';
 import { profileCheckpoint } from '../utils/startupProfiler.js';
 import { writeStderrLine } from '../utils/stdioHelpers.js';
@@ -195,13 +196,29 @@ export async function startInteractiveUI(
     // coordinates even though these listeners are owned and cleaned up.
     process.stdout.setMaxListeners(0);
   }
+  const appTree = (
+    <ErrorBoundary
+      onError={(error, info) => {
+        debugLogger.error(
+          `[FATAL_RENDER_ERROR] ${error.message}\n${info.componentStack ?? ''}\n${error.stack ?? ''}`,
+        );
+        // The fallback replaces AppWrapper, unmounting KeypressProvider and
+        // Ctrl+C handling. Schedule a graceful exit so the session does not
+        // hang (e.g. under the Kitty keyboard protocol where Ctrl+C is a
+        // keypress, not SIGINT).
+        setTimeout(() => {
+          void runExitCleanup().then(() => process.exit(1));
+        }, 5000);
+      }}
+    >
+      <AppWrapper />
+    </ErrorBoundary>
+  );
   const instance = render(
     process.env['DEBUG'] ? (
-      <React.StrictMode>
-        <AppWrapper />
-      </React.StrictMode>
+      <React.StrictMode>{appTree}</React.StrictMode>
     ) : (
-      <AppWrapper />
+      appTree
     ),
     {
       exitOnCtrlC: false,