diff --git a/playwright.samples.config.ts b/playwright.samples.config.ts
index 0582a44..ad21143 100644
--- a/playwright.samples.config.ts
+++ b/playwright.samples.config.ts
@@ -1,6 +1,6 @@
 import { defineConfig, devices } from "@playwright/test";
 
-const baseURL = process.env.GEO_SAMPLE_BASE_URL ?? "http://127.0.0.1:3000";
+const baseURL = process.env.GEO_SAMPLE_BASE_URL ?? "http://localhost:3000";
 const timeout = Number(process.env.GEO_SAMPLE_TIMEOUT_MS ?? "600000") + 60_000;
 
 export default defineConfig({
diff --git a/scripts/run-geo-sample-e2e.mjs b/scripts/run-geo-sample-e2e.mjs
index 27209e9..a36ae2b 100644
--- a/scripts/run-geo-sample-e2e.mjs
+++ b/scripts/run-geo-sample-e2e.mjs
@@ -46,7 +46,7 @@ export async function main(rawArgs = process.argv.slice(2)) {
   mkdirSync(reportDir, { recursive: true });
 
   const port = args.port ? Number(args.port) : await findAvailablePort(3000);
-  const baseURL = args.baseURL || `http://127.0.0.1:${port}`;
+  const baseURL = args.baseURL || baseURLForPort(port);
   const appDataDir = join(reportDir, "app-data");
   mkdirSync(appDataDir, { recursive: true });
 
@@ -70,7 +70,7 @@ export async function main(rawArgs = process.argv.slice(2)) {
         stdio: ["ignore", "pipe", "pipe"],
       });
       captureServerLogs(serverProcess, reportDir, runEnv);
-      await waitForServer(baseURL, 120000);
+      await waitForServer(baseURL, 120000, serverProcess);
     }
 
     status = await runPlaywright(runEnv, Boolean(args.headed));
@@ -108,6 +108,10 @@ export function parseArgs(rawArgs) {
   return parsed;
 }
 
+export function baseURLForPort(port) {
+  return `http://localhost:${port}`;
+}
+
 export function parseEnvFile(content) {
   const values = {};
   for (const line of content.split(/\r?\n/)) {
@@ -177,9 +181,14 @@ export function redact(text, secrets) {
   return next;
 }
 
-async function waitForServer(baseURL, timeoutMs) {
+export async function waitForServer(baseURL, timeoutMs, serverProcess = null) {
   const started = Date.now();
   while (Date.now() - started < timeoutMs) {
+    if (serverProcess?.exitCode !== null) {
+      throw new Error(
+        `dev server exited before ${baseURL} became ready; see server.log in the report directory`,
+      );
+    }
     try {
       const response = await fetch(baseURL, { method: "HEAD" });
       if (response.ok) return;
diff --git a/tests/sample-flow/runner.test.ts b/tests/sample-flow/runner.test.ts
index 4947943..1b7a0a1 100644
--- a/tests/sample-flow/runner.test.ts
+++ b/tests/sample-flow/runner.test.ts
@@ -1,9 +1,11 @@
 import { describe, expect, it } from "vitest";
 
 import {
+  baseURLForPort,
   parseEnvFile,
   preflight,
   redact,
+  waitForServer,
 } from "../../scripts/run-geo-sample-e2e.mjs";
 
 describe("run-geo-sample-e2e helpers", () => {
@@ -34,6 +36,10 @@ EMPTY=
     ).toThrow("DEEPSEEK_API_KEY is required for live sample E2E");
   });
 
+  it("uses localhost for Next dev URLs", () => {
+    expect(baseURLForPort(3000)).toBe("http://localhost:3000");
+  });
+
   it("redacts configured secrets from logs", () => {
     expect(
       redact("x-api-key: local-dev-key provider secret", [
@@ -42,4 +48,12 @@ EMPTY=
       ]),
     ).toBe("x-api-key: [REDACTED] [REDACTED]");
   });
+
+  it("fails fast when the dev server process exits before readiness", async () => {
+    await expect(
+      waitForServer("http://127.0.0.1:9", 1000, {
+        exitCode: 1,
+      }),
+    ).rejects.toThrow("dev server exited before http://127.0.0.1:9 became ready");
+  });
 });