diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
index a370b1c..feb8377 100644
--- a/.github/workflows/release.yml
+++ b/.github/workflows/release.yml
@@ -169,6 +169,20 @@ jobs:
       - name: Windows/Linux rehearsal (no publish)
         if: github.event_name == 'workflow_dispatch' && runner.os != 'macOS'
         run: npx electron-builder ${{ matrix.builder_args }} --publish never
+      - name: Exercise packaged demo runtime (own Electron, no system Chrome)
+        run: |
+          case "$RUNNER_OS" in
+            macOS)
+              app="dist/mac-arm64/LearnHarness.app/Contents"
+              node scripts/smoke-demo-runtime.mjs --standalone "$app/Resources/server/standalone" --runtime "$app/MacOS/LearnHarness" --browser
+              ;;
+            Windows)
+              node scripts/smoke-demo-runtime.mjs --standalone dist/win-unpacked/resources/server/standalone --runtime dist/win-unpacked/LearnHarness.exe --browser
+              ;;
+            Linux)
+              xvfb-run -a node scripts/smoke-demo-runtime.mjs --standalone dist/linux-unpacked/resources/server/standalone --runtime dist/linux-unpacked/learnharness --browser
+              ;;
+          esac
       - name: Save installers and update metadata
         uses: actions/upload-artifact@v7
         with:
diff --git a/next.config.ts b/next.config.ts
index 8c6c6b2..93ab859 100644
--- a/next.config.ts
+++ b/next.config.ts
@@ -55,6 +55,9 @@ const nextConfig: NextConfig = {
 	// caught it; unit tests run unbundled and never see it.
 	outputFileTracingIncludes: {
 		"*": [
+			// The standalone trace omitted this entire runtime-imported directory
+			// in 0.3.0, so importing puppeteer-core failed before browser startup.
+			"node_modules/@puppeteer/browsers/lib/browser-data/**/*.js",
 			"node_modules/pdfjs-dist/legacy/**/*",
 			"node_modules/pdfjs-dist/standard_fonts/**/*",
 			// Wave E (2026-10-10): pdf_render paints via @napi-rs/canvas — its
diff --git a/scripts/smoke-demo-runtime.mjs b/scripts/smoke-demo-runtime.mjs
new file mode 100644
index 0000000..4030111
--- /dev/null
+++ b/scripts/smoke-demo-runtime.mjs
@@ -0,0 +1,179 @@
+/**
+ * Import the demo dependency graph from ONLY a standalone payload. With --browser,
+ * also drive the packaged app's own --browser-service (never system Chrome).
+ * No server, model, keys, installed app UI, or production diagnostic route needed.
+ *
+ * node scripts/smoke-demo-runtime.mjs --standalone <dir> --runtime <electron binary> [--browser]
+ * --runtime defaults to host Node for the import-only gate.
+ */
+import assert from "node:assert/strict";
+import { spawn, spawnSync } from "node:child_process";
+import * as fs from "node:fs";
+import { createRequire, registerHooks } from "node:module";
+import * as os from "node:os";
+import * as path from "node:path";
+import { fileURLToPath, pathToFileURL } from "node:url";
+
+/** @param {Record<string, string | undefined>} env @param {string} home @returns {Record<string, string | undefined>} */
+export function probeEnv(env, home) {
+	const clean = Object.fromEntries(Object.entries(env).filter(([key]) =>
+		!/KEY|TOKEN|SECRET|PASSWORD|CREDENTIAL/i.test(key) &&
+		!/^(AWS_|GOOGLE_|GCLOUD_|CLOUDSDK_|AZURE_|ANTHROPIC_|OPENAI_|OPENROUTER_|GEMINI_)/.test(key) &&
+		!["NODE_OPTIONS", "NODE_PATH", "LH_DEV_URL", "ELECTRON_RUN_AS_NODE"].includes(key)));
+	return {
+		...clean,
+		HOME: home, USERPROFILE: home,
+		APPDATA: path.join(home, "config"), LOCALAPPDATA: path.join(home, "local"),
+		XDG_CONFIG_HOME: path.join(home, "config"), XDG_CACHE_HOME: path.join(home, "cache"),
+		LH_DATA_DIR: path.join(home, "data"), LH_AUTH_FILE: path.join(home, "auth.json"),
+		LH_IGNORE_ENV_KEYS: "1", NODE_ENV: "production",
+	};
+}
+
+export function verifyDemoRuntime(standalone, runtime = process.execPath, browser = false) {
+	const home = fs.mkdtempSync(path.join(os.tmpdir(), "lh-demo-runtime-"));
+	try {
+		fs.writeFileSync(path.join(home, "auth.json"), "{}\n", { mode: 0o600 });
+		const result = spawnSync(runtime, [fileURLToPath(import.meta.url), "--probe", path.resolve(standalone), ...(browser ? ["--browser"] : [])], {
+			cwd: home,
+			env: { ...probeEnv(process.env, home), ELECTRON_RUN_AS_NODE: "1" },
+			encoding: "utf8", timeout: 60_000, maxBuffer: 128 * 1024,
+		});
+		if (result.status !== 0 || result.error) {
+			throw new Error(`demo runtime probe failed (${result.error?.message ?? result.status}):\n${result.stdout ?? ""}${result.stderr ?? ""}`);
+		}
+		process.stdout.write(result.stdout);
+	} finally {
+		fs.rmSync(home, { recursive: true, force: true });
+	}
+}
+
+async function importPayload(standalone) {
+	const root = fs.realpathSync(standalone);
+	const inside = (file) => {
+		const relative = path.relative(root, fs.realpathSync(file));
+		assert.ok(relative !== ".." && !relative.startsWith(`..${path.sep}`) && !path.isAbsolute(relative),
+			`dependency escaped standalone payload: ${file}`);
+	};
+	const require = createRequire(path.join(root, "server.js"));
+	const entry = require.resolve("puppeteer-core");
+	inside(entry); // require.resolve must not silently fall back to checkout node_modules.
+	const loaded = new Set();
+	const hooks = registerHooks({
+		resolve(specifier, context, nextResolve) {
+			const result = nextResolve(specifier, context);
+			if (result.url.startsWith("file:")) {
+				inside(fileURLToPath(result.url));
+				loaded.add(result.url);
+			} else {
+				assert.ok(result.url.startsWith("node:"), `unexpected dependency URL: ${result.url}`);
+			}
+			return result;
+		},
+	});
+	try {
+		const { default: puppeteer } = await import(pathToFileURL(entry).href);
+		assert.equal(typeof puppeteer.connect, "function");
+		console.log(`[smoke-demo-runtime] puppeteer-core import ok; ${loaded.size} modules confined to ${root}`);
+		return { puppeteer, hooks };
+	} catch (error) {
+		hooks.deregister();
+		throw error;
+	}
+}
+
+async function browserProbe(puppeteer) {
+	assert.ok(process.versions.electron, "--browser requires a packaged Electron --runtime binary");
+	const home = process.env.HOME;
+	const env = { ...process.env };
+	delete env.ELECTRON_RUN_AS_NODE;
+	delete env.LH_DEV_URL;
+	const helper = spawn(process.execPath, [
+		"--browser-service", `--user-data-dir=${path.join(home, "browser-profile")}`,
+		"--disable-background-networking", "--disable-component-update", "--no-proxy-server",
+		// Hosted Linux runners disallow Chromium's unprivileged sandbox.
+		...(process.platform === "linux" ? ["--no-sandbox"] : []),
+	], { cwd: home, env, stdio: ["pipe", "pipe", "pipe"] });
+	let output = "";
+	let errors = "";
+	helper.stderr.on("data", (chunk) => { errors = (errors + chunk).slice(-16_000); });
+	const closed = new Promise((resolve) => helper.once("close", (code, signal) => resolve({ code, signal })));
+	let browser;
+	try {
+		const port = await new Promise((resolve, reject) => {
+			const timer = setTimeout(() => reject(new Error("browser-service handshake timed out")), 15_000);
+			helper.once("error", (err) => { clearTimeout(timer); reject(err); });
+			helper.once("exit", (code) => { clearTimeout(timer); reject(new Error(`browser-service exited early: ${code}`)); });
+			helper.stdout.on("data", (chunk) => {
+				output = (output + chunk).slice(-16_000);
+				const match = output.match(/^BROWSER_SERVICE_CDP (\d+)\r?$/m);
+				if (match) { clearTimeout(timer); resolve(Number(match[1])); }
+			});
+		});
+		const info = await (await fetch(`http://127.0.0.1:${port}/json/version`, { signal: AbortSignal.timeout(5000) })).json();
+		browser = await puppeteer.connect({ browserWSEndpoint: info.webSocketDebuggerUrl, defaultViewport: null, protocolTimeout: 10_000 });
+		// Electron CDP has no Target.createTarget: use the helper's existing page.
+		const pages = await browser.pages();
+		const page = pages.find((candidate) => candidate.target().type() === "page");
+		assert.ok(page, "browser-service has no page target");
+		const failures = [];
+		page.on("console", (msg) => { if (msg.type() === "error") failures.push(msg.text()); });
+		page.on("pageerror", (err) => failures.push(String(err)));
+		page.on("requestfailed", (req) => failures.push(`failed request: ${req.url()}`));
+		await page.setRequestInterception(true);
+		page.on("request", (req) => {
+			if (/^(file:|about:|data:)/.test(req.url())) void req.continue();
+			else { failures.push(`unexpected network request: ${req.url()}`); void req.abort(); }
+		});
+		const html = path.join(home, "demo.html");
+		fs.writeFileSync(html, '<!doctype html><meta charset="utf-8"><button id="increment">Increment</button><output id="count">0</output><script>document.querySelector("#increment").onclick = () => { document.querySelector("#count").textContent = "1"; };</script>');
+		await page.goto(pathToFileURL(html).href, { waitUntil: "load", timeout: 10_000 });
+		assert.equal(await page.$eval("#count", (element) => element.textContent), "0");
+		await page.click("#increment");
+		assert.equal(await page.$eval("#count", (element) => element.textContent), "1");
+		await page.goto("about:blank");
+		assert.equal(await page.$("#increment"), null, "page state was not cleared");
+		assert.deepEqual(failures, [], "demo console/page/network errors");
+		console.log("[smoke-demo-runtime] packaged browser-service: JS button 0 → 1, clean console/page, page reset ok (no Chrome fallback)");
+	} catch (err) {
+		throw new Error(`${err.stack ?? err}\n--- browser-service output ---\n${output}\n${errors}`);
+	} finally {
+		browser?.disconnect();
+		helper.stdin.end(); // The shipping lifetime contract: EOF must quit the helper.
+		let timer;
+		const result = await Promise.race([
+			closed,
+			new Promise((resolve) => { timer = setTimeout(() => resolve(null), 5000); }),
+		]);
+		clearTimeout(timer);
+		if (!result) {
+			helper.kill("SIGKILL");
+			await closed;
+			throw new Error("browser-service did not exit on stdin EOF; force-killed");
+		}
+		assert.deepEqual(result, { code: 0, signal: null }, "browser-service shutdown failed");
+		console.log("[smoke-demo-runtime] browser-service exited cleanly on stdin EOF (no resident helper)");
+	}
+}
+
+async function main() {
+	const args = process.argv.slice(2);
+	if (args[0] === "--probe") {
+		const { puppeteer, hooks } = await importPayload(args[1]);
+		try {
+			if (args.includes("--browser")) await browserProbe(puppeteer);
+		} finally { hooks.deregister(); }
+		return;
+	}
+	const value = (name, fallback) => {
+		const index = args.indexOf(name);
+		if (index < 0) return fallback;
+		assert.ok(args[index + 1] && !args[index + 1].startsWith("--"), `${name} requires a path`);
+		return path.resolve(args[index + 1]);
+	};
+	verifyDemoRuntime(value("--standalone", path.resolve(import.meta.dirname, "../.next/standalone")), value("--runtime", process.execPath), args.includes("--browser"));
+}
+
+if (process.argv[1] && path.resolve(process.argv[1]) === fileURLToPath(import.meta.url)) {
+	main().catch((err) => { console.error(`[smoke-demo-runtime] FAIL: ${err.stack ?? err}`); process.exitCode = 1; });
+}
diff --git a/scripts/smoke-server.mjs b/scripts/smoke-server.mjs
index 5721d01..53b53e6 100644
--- a/scripts/smoke-server.mjs
+++ b/scripts/smoke-server.mjs
@@ -25,6 +25,7 @@
  * way, same day).
  */
 import { spawn } from "node:child_process";
+import { probeEnv, verifyDemoRuntime } from "./smoke-demo-runtime.mjs";
 import { createRequire } from "node:module";
 import * as fs from "node:fs";
 import * as http from "node:http";
@@ -76,6 +77,9 @@ function get(url) {
 }
 
 async function main() {
+	// HTTP boot alone never imports the dynamically loaded demo engine.
+	// Fail before packaging if its standalone dependency graph is incomplete.
+	verifyDemoRuntime(STANDALONE, RUNTIME);
 	const port = await freePort();
 	const url = `http://127.0.0.1:${port}`;
 	const home = fs.mkdtempSync(path.join(os.tmpdir(), "lh-smoke-"));
@@ -104,7 +108,7 @@ async function main() {
 	const child = spawn(RUNTIME, [SERVER], {
 		cwd: STANDALONE,
 		env: {
-			...process.env,
+			...probeEnv(process.env, home),
 			...(ELECTRON_MODE ? { ELECTRON_RUN_AS_NODE: "1" } : {}),
 			NODE_ENV: "production",
 			PORT: String(port),
diff --git a/tests/demo-runtime-payload.test.ts b/tests/demo-runtime-payload.test.ts
new file mode 100644
index 0000000..eeca601
--- /dev/null
+++ b/tests/demo-runtime-payload.test.ts
@@ -0,0 +1,94 @@
+/** No display, real browser, installed app, or production dependency tree needed. */
+import assert from "node:assert/strict";
+import { spawnSync } from "node:child_process";
+import * as fs from "node:fs";
+import * as os from "node:os";
+import * as path from "node:path";
+import { describe, it } from "node:test";
+import { fileURLToPath, pathToFileURL } from "node:url";
+import { probeEnv } from "../scripts/smoke-demo-runtime.mjs";
+
+const script = fileURLToPath(new URL("../scripts/smoke-demo-runtime.mjs", import.meta.url));
+
+function withPayload(test: (fixture: {
+	root: string;
+	write: (relative: string, content: string) => void;
+	run: () => ReturnType<typeof spawnSync>;
+}) => void) {
+	const root = fs.mkdtempSync(path.join(os.tmpdir(), "lh-demo-payload-test-"));
+	const write = (relative: string, content: string) => {
+		const file = path.join(root, relative);
+		fs.mkdirSync(path.dirname(file), { recursive: true });
+		fs.writeFileSync(file, content);
+	};
+	try {
+		write("server.js", "// fixture");
+		write("node_modules/puppeteer-core/package.json", JSON.stringify({ name: "puppeteer-core", type: "module", main: "lib/index.js" }));
+		write("node_modules/puppeteer-core/lib/index.js", 'import "./browser-data/browser-data.js"; export default { connect() {} };');
+		test({ root, write, run: () => spawnSync(process.execPath, [script, "--standalone", root], {
+			encoding: "utf8", timeout: 10_000,
+		}) });
+	} finally {
+		fs.rmSync(root, { recursive: true, force: true });
+	}
+}
+
+describe("demo standalone dependency gate", () => {
+	it("imports a complete payload and does not change it", () => {
+		withPayload(({ root, write, run }) => {
+			write("node_modules/puppeteer-core/lib/browser-data/browser-data.js", "export const fixture = true;");
+			const before = fs.readdirSync(root, { recursive: true });
+			const result = run();
+			assert.equal(result.status, 0, String(result.stderr));
+			assert.match(String(result.stdout), /puppeteer-core import ok/);
+			assert.deepEqual(fs.readdirSync(root, { recursive: true }), before);
+		});
+	});
+
+	it("fails when a transitive runtime subdirectory is missing", () => {
+		withPayload(({ root, run }) => {
+			const before = fs.readdirSync(root, { recursive: true });
+			const result = run();
+			assert.equal(result.status, 1);
+			assert.match(String(result.stderr), /ERR_MODULE_NOT_FOUND/);
+			assert.match(String(result.stderr), /browser-data/);
+			assert.deepEqual(fs.readdirSync(root, { recursive: true }), before);
+		});
+	});
+
+	it("rejects imports outside the payload even when they resolve successfully", () => {
+		withPayload(({ write, run }) => {
+			// A sibling file, not just a missing file: resolution succeeds but confinement must fail.
+			const sibling = fs.mkdtempSync(path.join(os.tmpdir(), "lh-demo-outside-"));
+			try {
+				const external = path.join(sibling, "dependency.mjs");
+				fs.writeFileSync(external, "export const outside = true;");
+				write("node_modules/puppeteer-core/lib/index.js", `import ${JSON.stringify(pathToFileURL(external).href)}; export default { connect() {} };`);
+				const result = run();
+				assert.equal(result.status, 1);
+				assert.match(String(result.stderr), /dependency escaped standalone payload/);
+			} finally { fs.rmSync(sibling, { recursive: true, force: true }); }
+		});
+	});
+
+	it("cannot substitute the checkout's Puppeteer for an absent payload package", () => {
+		withPayload(({ root, run }) => {
+			fs.rmSync(path.join(root, "node_modules"), { recursive: true });
+			const result = run();
+			assert.equal(result.status, 1);
+			assert.doesNotMatch(String(result.stdout), /import ok/);
+		});
+	});
+
+	it("strips secrets and uses only scratch data/auth/profile locations", () => {
+		const original = { PATH: "/bin", API_KEY: "fake", GH_TOKEN: "fake", MY_SECRET: "fake", PASSWORD: "fake", NODE_OPTIONS: "--require anything", NODE_PATH: "/outside", ELECTRON_RUN_AS_NODE: "1", LH_DEV_URL: "http://localhost", LH_DATA_DIR: "/real", LH_AUTH_FILE: "/real/auth.json", GOOGLE_APPLICATION_CREDENTIALS: "/real/google.json", AWS_SHARED_CREDENTIALS_FILE: "/real/aws", AWS_PROFILE: "real-profile", CLOUDSDK_CONFIG: "/real/gcloud" };
+		const env = probeEnv(original, "/scratch");
+		for (const key of ["API_KEY", "GH_TOKEN", "MY_SECRET", "PASSWORD", "NODE_OPTIONS", "NODE_PATH", "ELECTRON_RUN_AS_NODE", "LH_DEV_URL", "GOOGLE_APPLICATION_CREDENTIALS", "AWS_SHARED_CREDENTIALS_FILE", "AWS_PROFILE", "CLOUDSDK_CONFIG"]) assert.equal(key in env, false, key);
+		assert.equal(env.PATH, "/bin");
+		assert.equal(env.LH_DATA_DIR, path.join("/scratch", "data"));
+		assert.equal(env.LH_AUTH_FILE, path.join("/scratch", "auth.json"));
+		assert.equal(env.LH_IGNORE_ENV_KEYS, "1");
+		assert.equal(env.HOME, "/scratch");
+		assert.equal(original.API_KEY, "fake");
+	});
+});