fix: forward Inertia headers through preview proxy

Preserves Inertia navigation inside preview panel
Forwards request and response Inertia headers
Adds preview proxy header passthrough tests

Author: btriapitsyn

packages/web/server/lib/preview/proxy-runtime.js

@@ -3,6 +3,8 @@ const TOKEN_COOKIE_NAME = 'oc_preview_token';
 const TOKEN_QUERY_PARAM = 'oc_preview_token';
 const CLIENT_TOKEN_QUERY_PARAM = 'oc_client_token';
 const URL_AUTH_TOKEN_QUERY_PARAM = 'oc_url_token';
+const PREVIEW_PASSTHROUGH_REQUEST_HEADERS = ['x-inertia', 'x-inertia-version'];
+const PREVIEW_PASSTHROUGH_RESPONSE_HEADERS = ['x-inertia', 'x-inertia-location'];
 
 const LOOPBACK_HOSTS = new Set([
   'localhost',
@@ -25,6 +27,34 @@ const parsePreviewResourcePath = (url) => {
   }
 };
 
+const readHeader = (headers, name) => {
+  if (!headers || typeof headers !== 'object') return undefined;
+  const direct = headers[name];
+  if (direct !== undefined) return direct;
+  const lowerName = name.toLowerCase();
+  const key = Object.keys(headers).find((entry) => entry.toLowerCase() === lowerName);
+  return key ? headers[key] : undefined;
+};
+
+export const applyPreviewPassthroughRequestHeaders = (req, proxyReq) => {
+  for (const headerName of PREVIEW_PASSTHROUGH_REQUEST_HEADERS) {
+    const value = readHeader(req?.headers, headerName);
+    if (value !== undefined) {
+      proxyReq.setHeader(headerName, value);
+    }
+  }
+};
+
+export const applyPreviewPassthroughResponseHeaders = (proxyRes, res) => {
+  if (!res || res.headersSent || typeof res.setHeader !== 'function') return;
+  for (const headerName of PREVIEW_PASSTHROUGH_RESPONSE_HEADERS) {
+    const value = readHeader(proxyRes?.headers, headerName);
+    if (value !== undefined) {
+      res.setHeader(headerName, value);
+    }
+  }
+};
+
 const previewResourceNoiseRuleSets = [
   {
     name: 'vite',
@@ -1412,14 +1442,16 @@ export const createPreviewProxyRuntime = ({
         return `${strippedPath}${withoutUrlAuthToken}`;
       },
       on: {
-        proxyReq: (proxyReq) => {
+        proxyReq: (proxyReq, req) => {
+          applyPreviewPassthroughRequestHeaders(req, proxyReq);
           // Keep local dev servers from receiving OpenChamber credentials.
           proxyReq.removeHeader('cookie');
           proxyReq.removeHeader('authorization');
           proxyReq.removeHeader('x-openchamber-ui-session');
           proxyReq.setHeader('accept-encoding', 'identity');
         },
-        proxyRes: responseInterceptor(async (responseBuffer, proxyRes, req) => {
+        proxyRes: responseInterceptor(async (responseBuffer, proxyRes, req, res) => {
+          applyPreviewPassthroughResponseHeaders(proxyRes, res);
           // Per-response nonce lets the injected bridge run under the dev
           // server's CSP without dropping its script restrictions wholesale.
           const bridgeNonce = crypto.randomBytes(16).toString('base64');

packages/web/server/lib/preview/proxy-runtime.test.js

@@ -1,6 +1,8 @@
 import { describe, expect, it } from 'vitest';
 
 import {
+  applyPreviewPassthroughRequestHeaders,
+  applyPreviewPassthroughResponseHeaders,
   classifyPreviewNavigation,
   classifyPreviewResourceError,
   normalizeProxyTargetUrl,
@@ -16,6 +18,47 @@ const rewrite = (bodyText, kind) => rewritePreviewBody({
   targetOrigin: 'http://127.0.0.1:3000',
 });
 
+describe('preview Inertia header passthrough', () => {
+  it('forwards Inertia request headers to the preview target', () => {
+    const forwarded = new Map();
+    const proxyReq = {
+      setHeader: (name, value) => forwarded.set(name, value),
+    };
+
+    applyPreviewPassthroughRequestHeaders({
+      headers: {
+        'x-inertia': 'true',
+        'x-inertia-version': 'asset-hash',
+        'x-unrelated': 'ignored',
+      },
+    }, proxyReq);
+
+    expect(forwarded.get('x-inertia')).toBe('true');
+    expect(forwarded.get('x-inertia-version')).toBe('asset-hash');
+    expect(forwarded.has('x-unrelated')).toBe(false);
+  });
+
+  it('forwards Inertia response headers back to the preview client', () => {
+    const forwarded = new Map();
+    const res = {
+      headersSent: false,
+      setHeader: (name, value) => forwarded.set(name, value),
+    };
+
+    applyPreviewPassthroughResponseHeaders({
+      headers: {
+        'x-inertia': 'true',
+        'x-inertia-location': 'http://127.0.0.1:8000/login',
+        'x-unrelated': 'ignored',
+      },
+    }, res);
+
+    expect(forwarded.get('x-inertia')).toBe('true');
+    expect(forwarded.get('x-inertia-location')).toBe('http://127.0.0.1:8000/login');
+    expect(forwarded.has('x-unrelated')).toBe(false);
+  });
+});
+
 describe('preview resource error classification', () => {
   it('suppresses Astro/Vite stylesheet modules reported as failed scripts', () => {
     expect(classifyPreviewResourceError({