diff --git a/README.md b/README.md
index e3f9cbf..49ae306 100644
--- a/README.md
+++ b/README.md
@@ -4,7 +4,7 @@
 
 Raidy is a raid scheduling project for Discord statics: the web console is where everyone plans, and Discord carries the announcements. One Go process runs the Discord bot, web API, scheduler, and production web assets, backed by PostgreSQL.
 
-**Status:** `v0.0.18` is an early development snapshot.
+**Status:** `v0.0.19` is an early development snapshot.
 
 ```text
 backend/     Go service, Discord interactions, web API, PostgreSQL migrations
@@ -60,8 +60,8 @@ The Go process applies pinned, embedded Goose migrations before opening the appl
 `web/product/` is the public product page, and the demo is the real app running against in-browser sample data. Neither needs the Go backend. From `web/`:
 
 ```sh
-npm run dev:product     # product page with live reload
-npm run dev:demo        # demo at /demo/ with live reload
+npm run dev:product     # product page and demo together, with live reload
+npm run dev:demo        # the demo alone, at /demo/
 npm run screenshots     # capture the app screenshots the page shows
 npm run build:pages     # build both into dist-pages/
 npm run preview:pages   # serve dist-pages/ as GitHub Pages does
diff --git a/web/e2e/product.spec.ts b/web/e2e/product.spec.ts
index b9e7d15..6dc0c91 100644
--- a/web/e2e/product.spec.ts
+++ b/web/e2e/product.spec.ts
@@ -12,6 +12,19 @@ test("the product page leads to the live demo and the code", async ({ page }) =>
   );
 });
 
+// Regression: the demo link was relative to the current page, and the
+// product server answered every path with the product page, so each click
+// added another /demo/ to the URL instead of opening the demo.
+test("the demo opens at /demo/ and leads back to the product page", async ({ page }) => {
+  await page.goto("/");
+  await page.getByRole("link", { name: "Try the demo" }).click();
+  await expect(page.getByRole("table", { name: /availability/i })).toBeVisible({ timeout: 30_000 });
+  expect(new URL(page.url()).pathname).toBe("/demo/");
+  await page.getByRole("link", { name: "About Raidy" }).click();
+  await expect(page.getByRole("heading", { level: 1 })).toHaveText("See which nights your whole static can raid.");
+  expect(new URL(page.url()).pathname).toBe("/");
+});
+
 test("tapping a night in the hero updates the Discord post", async ({ page }) => {
   await page.clock.setFixedTime(monday);
   await page.goto("/");
diff --git a/web/package-lock.json b/web/package-lock.json
index e3079fc..fea1fed 100644
--- a/web/package-lock.json
+++ b/web/package-lock.json
@@ -1,12 +1,12 @@
 {
   "name": "raidy-web",
-  "version": "0.0.18",
+  "version": "0.0.19",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "raidy-web",
-      "version": "0.0.18",
+      "version": "0.0.19",
       "dependencies": {
         "@fontsource-variable/geist": "^5.3.0",
         "@fontsource-variable/geist-mono": "^5.3.0",
diff --git a/web/package.json b/web/package.json
index 7c29a90..9677871 100644
--- a/web/package.json
+++ b/web/package.json
@@ -1,11 +1,11 @@
 {
   "name": "raidy-web",
   "private": true,
-  "version": "0.0.18",
+  "version": "0.0.19",
   "type": "module",
   "scripts": {
     "dev": "vite",
-    "dev:product": "vite --config vite.product.config.ts",
+    "dev:product": "node scripts/dev-site.mjs",
     "dev:demo": "vite --mode demo --base /demo/",
     "build": "tsc -b && vite build",
     "check": "tsc -b --pretty false",
@@ -14,7 +14,7 @@
     "test:e2e": "playwright test",
     "build:demo": "tsc -b && vite build --mode demo --base /demo/ --outDir dist-demo",
     "screenshots": "playwright test --config playwright.screenshots.config.ts",
-    "build:pages": "rm -rf dist-pages && tsc -b && vite build --config vite.product.config.ts && vite build --mode demo --base /demo/ --outDir dist-pages/demo",
+    "build:pages": "rm -rf dist-pages && tsc -b && vite build --config vite.product.config.ts && vite build --mode demo --base ./ --outDir dist-pages/demo",
     "preview:pages": "vite preview --config vite.product.config.ts"
   },
   "dependencies": {
diff --git a/web/playwright.config.ts b/web/playwright.config.ts
index 9d2d093..a6aec63 100644
--- a/web/playwright.config.ts
+++ b/web/playwright.config.ts
@@ -38,7 +38,8 @@ export default defineConfig({
       reuseExistingServer: !process.env.CI
     },
     {
-      command: `npx vite --config vite.product.config.ts --host 127.0.0.1 --port ${productPort} --strictPort`,
+      // The same command as `npm run dev:product`: the page plus the demo at /demo/.
+      command: `node scripts/dev-site.mjs --host 127.0.0.1 --port ${productPort} --strictPort`,
       url: `http://127.0.0.1:${productPort}/`,
       reuseExistingServer: !process.env.CI
     }
diff --git a/web/scripts/dev-site.mjs b/web/scripts/dev-site.mjs
new file mode 100644
index 0000000..753df66
--- /dev/null
+++ b/web/scripts/dev-site.mjs
@@ -0,0 +1,16 @@
+// Runs the product page and the demo together, so links to /demo/ work:
+// the product dev server forwards /demo/ to the demo dev server.
+import { spawn } from "node:child_process";
+
+const demo = ["--mode", "demo", "--base", "/demo/", "--host", "127.0.0.1", "--port", "5174", "--strictPort"];
+const product = ["--config", "vite.product.config.ts", ...process.argv.slice(2)];
+
+// Run vite directly rather than through npx, so stopping this script stops both servers.
+const servers = [demo, product].map((args) =>
+  spawn(process.execPath, ["node_modules/vite/bin/vite.js", ...args], { stdio: "inherit" })
+);
+
+const stop = () => servers.forEach((server) => server.kill());
+process.on("SIGINT", stop);
+process.on("SIGTERM", stop);
+servers.forEach((server) => server.on("exit", (code) => code && (stop(), process.exit(code))));
diff --git a/web/src/App.tsx b/web/src/App.tsx
index 332d92d..c73e6a8 100644
--- a/web/src/App.tsx
+++ b/web/src/App.tsx
@@ -10,7 +10,7 @@ import { Overview } from "@/features/overview/overview";
 import { SchedulePanel } from "@/features/schedule/schedule-panel";
 import { TeamPanel } from "@/features/team/team-panel";
 import { message } from "@/lib/format";
-import { isDemo, teamURL } from "@/lib/paths";
+import { isDemo, productURL, teamURL } from "@/lib/paths";
 import { applyTheme, type Theme, type ThemePreference } from "@/lib/theme";
 import { cn } from "@/lib/utils";
 
@@ -97,7 +97,7 @@ export default function App() {
 
   async function logout() {
     await api("/api/auth/logout", { method: "POST" });
-    location.assign("/");
+    location.assign(isDemo ? productURL : "/");
   }
 
   function chooseTheme(next: ThemePreference) {
@@ -232,7 +232,7 @@ function DemoBanner() {
           <span className="font-medium">Demo</span>
           <span className="text-muted-foreground"> · Sample data. Changes reset when you reload.</span>
         </span>
-        <a href="/" className="font-medium text-primary underline-offset-4 hover:underline">
+        <a href={productURL} className="font-medium text-primary underline-offset-4 hover:underline">
           About Raidy
         </a>
       </div>
diff --git a/web/src/lib/paths.ts b/web/src/lib/paths.ts
index 1f16715..5ed42ce 100644
--- a/web/src/lib/paths.ts
+++ b/web/src/lib/paths.ts
@@ -1,6 +1,9 @@
 /** True in the demo build, which runs the app against in-browser sample data. */
 export const isDemo = import.meta.env.MODE === "demo";
 
+/** The product page, which sits one level above the demo wherever the site is hosted. */
+export const productURL = "../";
+
 /** The app URL for a team: /app?team=N normally, /demo/?team=N in the demo. */
 export function teamURL(teamID: number) {
   return `${import.meta.env.BASE_URL}${isDemo ? "" : "app"}?team=${teamID}`;
diff --git a/web/src/product/product-page.tsx b/web/src/product/product-page.tsx
index 808818e..74ffd2b 100644
--- a/web/src/product/product-page.tsx
+++ b/web/src/product/product-page.tsx
@@ -67,7 +67,7 @@ export function ProductPage() {
   return (
     <div className="min-h-screen bg-background text-foreground">
       <header className="mx-auto flex h-16 max-w-6xl items-center gap-6 px-4 sm:px-6">
-        <a href="/" aria-label="Raidy home">
+        <a href="./" aria-label="Raidy home">
           <Wordmark className="text-xl" />
         </a>
         <nav className="hidden gap-6 text-sm text-muted-foreground sm:flex" aria-label="Sections">
diff --git a/web/vite.config.ts b/web/vite.config.ts
index 3bb1d2e..57fd05e 100644
--- a/web/vite.config.ts
+++ b/web/vite.config.ts
@@ -3,8 +3,11 @@ import { defineConfig } from "vite";
 import react from "@vitejs/plugin-react";
 import tailwindcss from "@tailwindcss/vite";
 
-export default defineConfig({
+export default defineConfig(({ mode }) => ({
   plugins: [react(), tailwindcss()],
+  // Each mode keeps its own dependency cache, so the app and the demo can run
+  // side by side without re-optimizing each other's dependencies.
+  cacheDir: mode === "demo" ? "node_modules/.vite-demo" : "node_modules/.vite",
   resolve: {
     alias: {
       "@": path.resolve(__dirname, "./src")
@@ -17,4 +20,4 @@ export default defineConfig({
       "/readyz": "http://127.0.0.1:8080"
     }
   }
-});
+}));
diff --git a/web/vite.product.config.ts b/web/vite.product.config.ts
index b139d89..7cc7404 100644
--- a/web/vite.product.config.ts
+++ b/web/vite.product.config.ts
@@ -3,15 +3,25 @@ import { defineConfig } from "vite";
 import react from "@vitejs/plugin-react";
 import tailwindcss from "@tailwindcss/vite";
 
-// The product page at the site root; the demo build is added under /demo/.
+// The product page at the site root; the demo build is added under demo/.
+// Paths are relative so the site works on a custom domain or under
+// joshchen-dev.github.io/raidy/ alike.
 export default defineConfig({
   root: path.resolve(__dirname, "product"),
+  base: "./",
+  cacheDir: path.resolve(__dirname, "node_modules/.vite-product"),
+  // No single-page fallback: an unknown path is a 404, not the product page again.
+  appType: "mpa",
   plugins: [react(), tailwindcss()],
   resolve: {
     alias: {
       "@": path.resolve(__dirname, "./src")
     }
   },
+  server: {
+    // `npm run dev:product` also starts the demo; serve it at /demo/ here.
+    proxy: { "/demo": { target: "http://127.0.0.1:5174", ws: true } }
+  },
   build: {
     outDir: path.resolve(__dirname, "dist-pages"),
     emptyOutDir: false