feat: bind to 0.0.0.0 in CI

Author: V3RON

packages/bundler-metro/src/factory.ts

@@ -66,9 +66,16 @@ export const getMetroInstance = async (
     .use('/status', getStatusMiddleware(projectRoot));
 
   const ready = waitForBundler(reporter, abortSignal);
-  const metroBindHost = harnessConfig.host?.trim();
+  const metroBindHost =
+    harnessConfig.host?.trim() ??
+    (process.env.CI ? '0.0.0.0' : undefined);
+
+  // In CI, bind to all interfaces to avoid connectivity issues on macOS runners
+  // where Metro is intermittently unreachable from the iOS simulator when bound
+  // to localhost only.
   if (metroBindHost) {
-    logger.debug(`Binding Metro server to host ${metroBindHost}`);
+    const source = harnessConfig.host?.trim() ? 'config' : 'CI default';
+    logger.debug(`Binding Metro server to host ${metroBindHost} (${source})`);
   }
 
   const maybeServer = await Metro.runServer(config, {

website/src/docs/getting-started/configuration.mdx

@@ -84,7 +84,7 @@ For Expo projects, the `entryPoint` should be set to the path specified in the `
 | `appRegistryComponentName`         | **Required.** Name of the component registered with AppRegistry.              |
 | `runners`                          | **Required.** Array of test runners (at least one required).                  |
 | `defaultRunner`                    | Default runner to use when none specified.                                    |
-| `host`                             | Hostname or IP address to bind the Metro server to (default: Metro default).  |
+| `host`                             | Hostname or IP address to bind the Metro server to. Defaults to `0.0.0.0` in CI (`process.env.CI` is set) to avoid connectivity issues on macOS runners where Metro may be unreachable from the iOS simulator when bound to `localhost`. |
 | `bridgeTimeout`                    | Bridge timeout in milliseconds (default: `60000`).                            |
 | `bundleStartTimeout`               | Bundle start timeout in milliseconds (default: `15000`).                      |
 | `maxAppRestarts`                   | Maximum number of app restarts when app fails to report ready (default: `2`). |

website/src/docs/guides/ci-cd.md

@@ -225,6 +225,18 @@ If you're using frameworks like **Expo** or **Rock**, you'll benefit from sophis
 
 This makes caching much more reliable and reduces the need for manual cache management.
 
+## Metro Networking in CI
+
+When running in CI (i.e. the `CI` environment variable is set), React Native Harness automatically binds the Metro server to `0.0.0.0` (all network interfaces) instead of the default `localhost`. This works around intermittent connectivity issues on macOS runners where the iOS Simulator cannot reach Metro when it is bound to `localhost` only.
+
+If you need Metro to bind to a specific interface, set the `host` option in your config — it always takes precedence over the CI default:
+
+```js
+const config = {
+  host: '192.168.1.100',
+};
+```
+
 ## Adapting for Your Project
 
 ### React Native Community CLI Projects