diff --git a/src/validation/layer2.ts b/src/validation/layer2.ts
index c9f83f6..b95fb19 100644
--- a/src/validation/layer2.ts
+++ b/src/validation/layer2.ts
@@ -1,17 +1,111 @@
+import { spawn } from "node:child_process";
+import { access } from "node:fs/promises";
+import { resolve } from "node:path";
+
 export type Layer2Input = {
   railsDir: string;
-  healthPath?: string;
-  bootTimeoutMs?: number;
+  timeoutMs?: number;
 };
 
 export type Layer2Result = {
   pass: boolean;
-  port: number;
-  healthStatus: number | null;
+  command: string;
+  exitCode: number | null;
+  durationMs: number;
   stderrTail?: string;
 };
 
+const DEFAULT_TIMEOUT_MS = 300_000;
+
 export async function runLayer2(input: Layer2Input): Promise<Layer2Result> {
-  void input;
-  throw new Error("runLayer2 not implemented: pick random port, spawn bin/rails server -p <port> -b 127.0.0.1, poll healthPath (default /up) until 200 or bootTimeoutMs, then SIGTERM");
+  const timeoutMs = input.timeoutMs ?? DEFAULT_TIMEOUT_MS;
+  const start = Date.now();
+
+  if (!(await exists(input.railsDir))) {
+    return {
+      pass: false,
+      command: "stat",
+      exitCode: null,
+      durationMs: Date.now() - start,
+      stderrTail: `railsDir does not exist: ${input.railsDir}`,
+    };
+  }
+
+  const useMise = await commandAvailable("mise");
+
+  const bundleCheck = await runRails(input.railsDir, ["bundle", "check"], timeoutMs, useMise);
+  if (bundleCheck.exitCode !== 0) {
+    const bundleInstall = await runRails(input.railsDir, ["bundle", "install"], timeoutMs, useMise);
+    if (bundleInstall.exitCode !== 0) {
+      return failed("bundle install", bundleInstall, start, useMise);
+    }
+  }
+
+  const routes = await runRails(input.railsDir, ["bin/rails", "routes"], timeoutMs, useMise);
+  if (routes.exitCode !== 0) {
+    return failed("bin/rails routes", routes, start, useMise);
+  }
+
+  return {
+    pass: true,
+    command: withPrefix("bin/rails routes", useMise),
+    exitCode: 0,
+    durationMs: Date.now() - start,
+  };
+}
+
+function failed(action: string, result: RunResult, start: number, useMise: boolean): Layer2Result {
+  return {
+    pass: false,
+    command: withPrefix(action, useMise),
+    exitCode: result.exitCode,
+    durationMs: Date.now() - start,
+    stderrTail: tail(result.stderr, 30),
+  };
+}
+
+function withPrefix(action: string, useMise: boolean): string {
+  return useMise ? `mise exec -- ${action}` : action;
+}
+
+type RunResult = { exitCode: number | null; stderr: string };
+
+function runRails(cwd: string, argv: readonly string[], timeoutMs: number, useMise: boolean): Promise<RunResult> {
+  const [command, ...rest] = useMise ? ["mise", "exec", "--", ...argv] : argv;
+  return new Promise((resolvePromise) => {
+    const child = spawn(command!, rest, { cwd });
+    const stderrChunks: Buffer[] = [];
+    const timer = setTimeout(() => { child.kill("SIGTERM"); }, timeoutMs);
+
+    child.stderr.on("data", (c: Buffer) => stderrChunks.push(c));
+    child.on("close", (code) => {
+      clearTimeout(timer);
+      resolvePromise({ exitCode: code, stderr: Buffer.concat(stderrChunks).toString("utf8") });
+    });
+    child.on("error", () => {
+      clearTimeout(timer);
+      resolvePromise({ exitCode: null, stderr: Buffer.concat(stderrChunks).toString("utf8") });
+    });
+  });
+}
+
+async function commandAvailable(bin: string): Promise<boolean> {
+  return new Promise((resolvePromise) => {
+    const c = spawn("which", [bin]);
+    c.on("close", (code) => resolvePromise(code === 0));
+    c.on("error", () => resolvePromise(false));
+  });
+}
+
+async function exists(path: string): Promise<boolean> {
+  try {
+    await access(path);
+    return true;
+  } catch {
+    return false;
+  }
+}
+
+function tail(s: string, lines: number): string {
+  return s.split("\n").slice(-lines).join("\n");
 }
diff --git a/tests/smoke.test.ts b/tests/smoke.test.ts
index 653375b..7ebe9e4 100644
--- a/tests/smoke.test.ts
+++ b/tests/smoke.test.ts
@@ -16,11 +16,11 @@ test("runLayer1 rejects until implemented", async () => {
   );
 });
 
-test("runLayer2 rejects until implemented", async () => {
-  await assert.rejects(
-    runLayer2({ railsDir: "/tmp" }),
-    /not implemented/i,
-  );
+test("runLayer2 returns a failed result for a non-Rails directory", async () => {
+  const result = await runLayer2({ railsDir: "/tmp", timeoutMs: 10_000 });
+  assert.equal(result.pass, false);
+  assert.equal(typeof result.command, "string");
+  assert.equal(typeof result.durationMs, "number");
 });
 
 test("runLayer3 rejects until implemented", async () => {