From 36af558a4a91da70416dddc584c60f254d5ca9a3 Mon Sep 17 00:00:00 2001
From: Jack Carter <128555021+SunsetDrifter@users.noreply.github.com>
Date: Mon, 3 Aug 2026 13:32:38 +0200
Subject: [PATCH 1/3] fix: serve props JSON for /api data requests via
 middleware rewrite

The /api/:path* -> /ipa/:path* rewrite in next.config.mjs is applied by
Vercel's routing to client-side props fetches
(/_next/data/<buildId>/api/....json), but the data-request context is
lost and the prerendered page HTML is returned instead of JSON
(vercel/next.js#39669). The router then never receives pageProps, so the
API sidebar stays collapsed and the tab title shows undefined until a
full reload. This half of the bug only occurs on Vercel infrastructure;
the dev server and next start resolve rewrites for data requests
correctly, and #900 fixed only the /ipa redirect half.

Middleware rewrites preserve data-request semantics, so rewrite /api/*
to /ipa/* in middleware for data requests only (x-nextjs-data header).
Regular page requests fall through to the existing config rewrites, and
the /ipa -> /api canonical redirect is unchanged.
---
 src/middleware.js | 43 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 43 insertions(+)
 create mode 100644 src/middleware.js

diff --git a/src/middleware.js b/src/middleware.js
new file mode 100644
index 00000000..02d889d9
--- /dev/null
+++ b/src/middleware.js
@@ -0,0 +1,43 @@
+import { NextResponse } from 'next/server'
+
+// Client-side navigations fetch page props from /_next/data/<buildId>/api/....json.
+// Vercel's routing applies the /api/:path* -> /ipa/:path* rewrite from
+// next.config.mjs to those requests but loses the data-request context and
+// serves the page HTML instead of the props JSON, so the router never receives
+// pageProps (https://github.com/vercel/next.js/issues/39669). Middleware
+// rewrites keep data-request semantics, so map /api/* to /ipa/* here for data
+// requests only; regular page requests fall through to the config rewrites.
+export const config = {
+  matcher: [
+    '/api/:path*',
+    // Raw data-request paths, in case the runtime matches them un-normalized.
+    '/_next/data/:build/api.json',
+    '/_next/data/:build/api/:path*',
+  ],
+}
+
+export function middleware(request) {
+  const isDataRequest =
+    request.headers.get('x-nextjs-data') !== null ||
+    request.nextUrl.pathname.startsWith('/_next/data/')
+  if (!isDataRequest) {
+    return NextResponse.next()
+  }
+
+  const url = request.nextUrl.clone()
+  if (url.pathname.startsWith('/_next/data/')) {
+    url.pathname = url.pathname.replace(
+      /^(\/_next\/data\/[^/]+)\/api(\/|\.json$)/,
+      '$1/ipa$2'
+    )
+  } else if (url.pathname === '/api') {
+    url.pathname = '/ipa/introduction'
+  } else {
+    url.pathname = url.pathname.replace(/^\/api\//, '/ipa/')
+  }
+
+  if (url.pathname === request.nextUrl.pathname) {
+    return NextResponse.next()
+  }
+  return NextResponse.rewrite(url)
+}

From 72db67e55ac8646a2d33875905bdd3646decc9e6 Mon Sep 17 00:00:00 2001
From: Jack Carter <128555021+SunsetDrifter@users.noreply.github.com>
Date: Mon, 3 Aug 2026 13:37:56 +0200
Subject: [PATCH 2/3] fix: move /api data-request rewrite into existing
 proxy.js

Next 16 uses proxy.js and rejects builds where both middleware.js and
proxy.js exist; this repo already had src/proxy.js for the
/docs-static/_next asset rewrite. Fold the /api -> /ipa data-request
rewrite into it and drop middleware.js. Verified the proxy intercepts:
data responses now carry x-middleware-rewrite: /ipa/... and JSON bodies.
---
 src/middleware.js | 43 -------------------------------------------
 src/proxy.js      | 36 ++++++++++++++++++++++++++++++++++--
 2 files changed, 34 insertions(+), 45 deletions(-)
 delete mode 100644 src/middleware.js

diff --git a/src/middleware.js b/src/middleware.js
deleted file mode 100644
index 02d889d9..00000000
--- a/src/middleware.js
+++ /dev/null
@@ -1,43 +0,0 @@
-import { NextResponse } from 'next/server'
-
-// Client-side navigations fetch page props from /_next/data/<buildId>/api/....json.
-// Vercel's routing applies the /api/:path* -> /ipa/:path* rewrite from
-// next.config.mjs to those requests but loses the data-request context and
-// serves the page HTML instead of the props JSON, so the router never receives
-// pageProps (https://github.com/vercel/next.js/issues/39669). Middleware
-// rewrites keep data-request semantics, so map /api/* to /ipa/* here for data
-// requests only; regular page requests fall through to the config rewrites.
-export const config = {
-  matcher: [
-    '/api/:path*',
-    // Raw data-request paths, in case the runtime matches them un-normalized.
-    '/_next/data/:build/api.json',
-    '/_next/data/:build/api/:path*',
-  ],
-}
-
-export function middleware(request) {
-  const isDataRequest =
-    request.headers.get('x-nextjs-data') !== null ||
-    request.nextUrl.pathname.startsWith('/_next/data/')
-  if (!isDataRequest) {
-    return NextResponse.next()
-  }
-
-  const url = request.nextUrl.clone()
-  if (url.pathname.startsWith('/_next/data/')) {
-    url.pathname = url.pathname.replace(
-      /^(\/_next\/data\/[^/]+)\/api(\/|\.json$)/,
-      '$1/ipa$2'
-    )
-  } else if (url.pathname === '/api') {
-    url.pathname = '/ipa/introduction'
-  } else {
-    url.pathname = url.pathname.replace(/^\/api\//, '/ipa/')
-  }
-
-  if (url.pathname === request.nextUrl.pathname) {
-    return NextResponse.next()
-  }
-  return NextResponse.rewrite(url)
-}
diff --git a/src/proxy.js b/src/proxy.js
index e83805e3..57d1f305 100644
--- a/src/proxy.js
+++ b/src/proxy.js
@@ -1,10 +1,42 @@
 import { NextResponse } from 'next/server';
 
+// Client-side navigations fetch page props from /_next/data/<buildId>/api/....json.
+// Vercel's routing applies the /api/:path* -> /ipa/:path* rewrite from
+// next.config.mjs to those requests but loses the data-request context and
+// serves the page HTML instead of the props JSON
+// (https://github.com/vercel/next.js/issues/39669), so the router never
+// receives pageProps. Proxy rewrites keep data-request semantics, so map
+// /api/* to /ipa/* here for data requests only; regular page requests fall
+// through to the config rewrites, and the /ipa -> /api canonical redirect
+// is unchanged.
+function rewriteApiDataRequest(req) {
+    const isDataRequest =
+        req.headers.get('x-nextjs-data') !== null ||
+        req.nextUrl.pathname.startsWith('/_next/data/');
+    if (!isDataRequest) return null;
+
+    const url = req.nextUrl.clone();
+    if (url.pathname.startsWith('/_next/data/')) {
+        // Raw data-request path, in case the runtime matches it un-normalized.
+        url.pathname = url.pathname.replace(
+            /^(\/_next\/data\/[^/]+)\/api(\/|\.json$)/,
+            '$1/ipa$2',
+        );
+    } else if (url.pathname === '/api') {
+        url.pathname = '/ipa/introduction';
+    } else if (url.pathname.startsWith('/api/')) {
+        url.pathname = url.pathname.replace(/^\/api\//, '/ipa/');
+    }
+
+    if (url.pathname === req.nextUrl.pathname) return null;
+    return NextResponse.rewrite(url);
+}
+
 export function proxy(req) {
     if (req.nextUrl.href.includes('/docs-static/_next/'))
         return NextResponse.rewrite(
             req.nextUrl.href.replace('/docs-static/_next/', '/_next/'),
         );
 
-    return null;
-}
\ No newline at end of file
+    return rewriteApiDataRequest(req);
+}

From 037534b69a053153f778ba942f2101a058346b05 Mon Sep 17 00:00:00 2001
From: Jack Carter <128555021+SunsetDrifter@users.noreply.github.com>
Date: Mon, 3 Aug 2026 13:40:42 +0200
Subject: [PATCH 3/3] fix: map bare api.json data requests to
 ipa/introduction.json

The raw data-path fallback rewrote /_next/data/<build>/api.json to
/_next/data/<build>/ipa.json, but there is no /ipa index page; mirror
the /api -> /ipa/introduction rewrite instead.
---
 src/proxy.js | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/src/proxy.js b/src/proxy.js
index 57d1f305..eebb7926 100644
--- a/src/proxy.js
+++ b/src/proxy.js
@@ -18,10 +18,14 @@ function rewriteApiDataRequest(req) {
     const url = req.nextUrl.clone();
     if (url.pathname.startsWith('/_next/data/')) {
         // Raw data-request path, in case the runtime matches it un-normalized.
-        url.pathname = url.pathname.replace(
-            /^(\/_next\/data\/[^/]+)\/api(\/|\.json$)/,
-            '$1/ipa$2',
-        );
+        // Bare api.json maps to ipa/introduction.json to mirror the /api ->
+        // /ipa/introduction rewrite; there is no /ipa index page.
+        url.pathname = url.pathname
+            .replace(
+                /^(\/_next\/data\/[^/]+)\/api\.json$/,
+                '$1/ipa/introduction.json',
+            )
+            .replace(/^(\/_next\/data\/[^/]+)\/api\//, '$1/ipa/');
     } else if (url.pathname === '/api') {
         url.pathname = '/ipa/introduction';
     } else if (url.pathname.startsWith('/api/')) {