diff --git a/README.md b/README.md
index a591f32..f911603 100644
--- a/README.md
+++ b/README.md
@@ -77,23 +77,63 @@ tracks the migration from in-process execution to a durable, isolated worker.
 Requires Docker, Node.js 22, and npm. Go is required only when running the
 simulator tests directly on the host.
 
+For the newer public challenges, clone the independently maintained challenge
+repository beside this one. The current local runner reads those challenge
+packages from disk; a registry file alone cannot execute them. This is an
+explicit development setup, not yet a downloadable challenge-bundle release.
+
+```text
+roughstack/
+  challenges/
+  web-platform/
+```
+
+From a new `roughstack` directory:
+
 ```bash
+git clone https://github.com/roughstack/challenges.git
+git clone https://github.com/roughstack/web-platform.git
+cd web-platform
 npm ci
 cp .env.example .env.local
+BYTEARENA_ARENA_ROOTS=../challenges/challenges npm run arena:validate -- --all
 docker build -t roughstack-execution-runtime:latest ./sprite
 npm run docker:up
 npm run db:push
 npm run db:seed
 ```
 
-The app is served at `http://localhost:3100`.
+Open `http://localhost:3100/challenges/cache-pressure-easy`. The editor must
+show an incomplete scaffold, not the passing public baseline. Complete it and
+submit to see a real local run. `EXECUTION_MODE=local` in `.env.local` is required;
+`stub` emits synthetic UI-development results and must not be used to verify a
+challenge. The Docker Compose file mounts `../challenges` read-only into the web
+container, so a differently placed checkout needs an adjusted mount and
+`BYTEARENA_ARENA_ROOTS` path.
+
+To run the automated baseline-versus-scaffold check against the running stack:
+
+```bash
+ROUGHSTACK_REAL_ARENA_E2E=1 npx playwright test tests/e2e/contributor-loop.spec.ts
+```
+
+This check runs submitted code in Docker and asserts that the public baseline
+passes while the learner scaffold fails with a useful diagnostic. It is opt-in
+because it requires the separate challenge checkout, Docker access, and a live
+database. Use it only on a trusted local machine; the current Docker-backed
+development server is not a public untrusted-code service. The extracted
+`execution-runtime` repository owns SDK and protocol development. This local
+setup still builds its compatibility image from `web-platform/sprite`; moving
+that image to a versioned runtime release is separate work.
 
 ```bash
 npm run docker:logs            # tail the web container
-npm run docker:reset           # wipe volumes and rebuild from scratch
-npm run docker:down            # stop everything
+npm run docker:down            # stop everything without deleting data
 ```
 
+`npm run docker:reset` deletes the local Compose database volume; do not use it
+to troubleshoot an existing checkout without backing up data first.
+
 ---
 
 ## Verification
diff --git a/tests/e2e/contributor-loop.spec.ts b/tests/e2e/contributor-loop.spec.ts
new file mode 100644
index 0000000..fae0337
--- /dev/null
+++ b/tests/e2e/contributor-loop.spec.ts
@@ -0,0 +1,74 @@
+import { readFile } from "node:fs/promises";
+import path from "node:path";
+
+import { expect, test, type APIRequestContext } from "@playwright/test";
+
+const enabled = process.env.ROUGHSTACK_REAL_ARENA_E2E === "1";
+const challengeRoot = path.resolve(
+  process.env.ROUGHSTACK_CHALLENGES_ROOT ?? "../challenges",
+);
+const arenaRoot = path.join(challengeRoot, "challenges/cache-pressure-easy");
+
+interface SubmissionResponse {
+  id: string;
+}
+
+interface ResultResponse {
+  status: string;
+  error?: string;
+  result?: {
+    status: string;
+    metrics: Record<string, number>;
+    detail?: { run?: { workload_id?: string; duration_ns?: number } };
+    message?: string;
+  };
+}
+
+async function submitAndWait(
+  request: APIRequestContext,
+  code: string,
+): Promise<ResultResponse> {
+  const submission = await request.post("/api/submissions", {
+    data: { slug: "cache-pressure-easy", language: "GO", code },
+  });
+  expect(submission.ok(), await submission.text()).toBe(true);
+  const { id } = (await submission.json()) as SubmissionResponse;
+  expect(id).toBeTruthy();
+
+  const deadline = Date.now() + 180_000;
+  while (Date.now() < deadline) {
+    const response = await request.get(`/api/submissions/${id}`);
+    expect(response.ok(), await response.text()).toBe(true);
+    const body = (await response.json()) as ResultResponse;
+    if (body.status === "done" || body.status === "error") return body;
+    await new Promise((resolve) => setTimeout(resolve, 1000));
+  }
+  throw new Error(`Submission ${id} did not finish within 180 seconds`);
+}
+
+test("a contributor can run a public baseline and reject the learner scaffold", async ({
+  request,
+}) => {
+  test.skip(!enabled, "Set ROUGHSTACK_REAL_ARENA_E2E=1 for the local Docker acceptance check");
+  test.setTimeout(420_000);
+
+  const page = await request.get("/challenges/cache-pressure-easy");
+  expect(page.ok(), await page.text()).toBe(true);
+
+  const baseline = await readFile(path.join(arenaRoot, "starter/cache.go"), "utf8");
+  const scaffold = await readFile(path.join(arenaRoot, "learner/starter.go"), "utf8");
+  expect(scaffold).not.toBe(baseline);
+
+  const passing = await submitAndWait(request, baseline);
+  expect(passing, JSON.stringify(passing)).toMatchObject({
+    status: "done",
+    result: { status: "passed" },
+  });
+  expect(passing.result?.detail?.run?.workload_id).toBeTruthy();
+  expect(Object.keys(passing.result?.metrics ?? {}).length).toBeGreaterThan(0);
+
+  const failing = await submitAndWait(request, scaffold);
+  expect(failing.status, JSON.stringify(failing)).toBe("done");
+  expect(failing.result?.status).toBe("failed");
+  expect(failing.result?.message).toMatch(/TODO|build|test|failed/i);
+});