Add e2e test for kernel recovery after external kill

test/e2e/tests/notebooks-positron/notebook-kernel-external-kill.test.ts

@@ -0,0 +1,59 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (C) 2026 Posit Software, PBC. All rights reserved.
+ *  Licensed under the Elastic License 2.0. See LICENSE.txt for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+import { execSync } from 'child_process';
+import { expect, tags } from '../_test.setup';
+import { test } from './_test.setup.js';
+
+test.use({
+	suiteId: __filename
+});
+
+test.describe('Positron Notebooks: Kernel External Kill', {
+	tag: [tags.POSITRON_NOTEBOOKS]
+}, () => {
+
+	test('Python - detects kernel death and allows restart after external kill', {
+		annotation: [{ type: 'issue', description: 'https://github.com/posit-dev/positron/issues/12869' }]
+	}, async function ({ app }) {
+		const { notebooksPositron } = app.workbench;
+
+		await test.step('Create notebook and start Python kernel', async () => {
+			await notebooksPositron.newNotebook();
+			await notebooksPositron.kernel.select('Python');
+		});
+
+		await test.step('Execute cell to confirm kernel is working and get PID', async () => {
+			await notebooksPositron.addCodeToCell(0, 'import os; print(os.getpid())', { run: true });
+			await expect(notebooksPositron.cellOutput(0)).toBeVisible({ timeout: 30000 });
+		});
+
+		const pid = await test.step('Read kernel PID from cell output', async () => {
+			const outputText = await notebooksPositron.cellOutput(0).textContent();
+			const parsed = parseInt(outputText!.trim(), 10);
+			expect(parsed).toBeGreaterThan(0);
+			return parsed;
+		});
+
+		await test.step('Kill kernel process externally (simulating OOM kill)', async () => {
+			execSync(`kill -9 ${pid}`);
+		});
+
+		await test.step('Verify Positron detects kernel death', async () => {
+			await notebooksPositron.kernel.expectStatusToBe('disconnected', 30000);
+		});
+
+		await test.step('Restart kernel and verify it recovers', async () => {
+			await notebooksPositron.kernel.restart();
+			await notebooksPositron.kernel.expectStatusToBe('idle', 30000);
+		});
+
+		await test.step('Execute code after restart to confirm kernel is functional', async () => {
+			await notebooksPositron.addCodeToCell(1, 'print("recovered")', { run: true });
+			await expect(notebooksPositron.cellOutput(1)).toContainText('recovered', { timeout: 30000 });
+		});
+	});
+
+});