From eb72a6f009c9994c03c4686325e171569cd669df Mon Sep 17 00:00:00 2001
From: Matt Brophy <matt@brophy.org>
Date: Tue, 23 Sep 2025 14:29:58 -0400
Subject: [PATCH 1/2] Add back-compat for manifest  parameter

---
 .changeset/rare-jobs-remember.md              |  5 ++++
 .../react-router/lib/server-runtime/server.ts | 26 +++++++++++--------
 2 files changed, 20 insertions(+), 11 deletions(-)
 create mode 100644 .changeset/rare-jobs-remember.md

diff --git a/.changeset/rare-jobs-remember.md b/.changeset/rare-jobs-remember.md
new file mode 100644
index 0000000000..6ab9615576
--- /dev/null
+++ b/.changeset/rare-jobs-remember.md
@@ -0,0 +1,5 @@
+---
+"react-router": patch
+---
+
+[REMOVE] Follow up to https://github.com/remix-run/react-router/pull/14321 to avoid issues with rolling deployments
diff --git a/packages/react-router/lib/server-runtime/server.ts b/packages/react-router/lib/server-runtime/server.ts
index d3b78ae510..ad5ac91734 100644
--- a/packages/react-router/lib/server-runtime/server.ts
+++ b/packages/react-router/lib/server-runtime/server.ts
@@ -354,19 +354,15 @@ async function handleManifestRequest(
 
   let patches: Record<string, EntryRoute> = {};
 
-  if (url.searchParams.has("paths")) {
+  // Support both the old (`p`) and new formats (`paths`) to avoid issues during
+  // rolling deployments where an old client hits a new server
+  if (url.searchParams.has("p") || url.searchParams.has("paths")) {
     let paths = new Set<string>();
 
-    // In addition to responding with the patches for the requested paths, we
-    // need to include patches for each partial path so that we pick up any
-    // pathless/index routes below ancestor segments.  So if we
-    // get a request for `/parent/child`, we need to look for a match on `/parent`
-    // so that if a `parent._index` route exists we return it so it's available
-    // for client side matching if the user routes back up to `/parent`.
-    // This is the same thing we do on initial load in <Scripts> via
-    // `getPartialManifest()`
-    let pathParam = url.searchParams.get("paths") || "";
-    let requestedPaths = pathParam.split(",").filter(Boolean);
+    let requestedPaths = url.searchParams.has("paths")
+      ? (url.searchParams.get("paths") || "").split(",").filter(Boolean)
+      : url.searchParams.getAll("p");
+
     requestedPaths.forEach((path) => {
       if (!path.startsWith("/")) {
         path = `/${path}`;
@@ -378,6 +374,14 @@ async function handleManifestRequest(
       });
     });
 
+    // In addition to responding with the patches for the requested paths, we
+    // need to include patches for each partial path so that we pick up any
+    // pathless/index routes below ancestor segments.  So if we
+    // get a request for `/parent/child`, we need to look for a match on `/parent`
+    // so that if a `parent._index` route exists we return it so it's available
+    // for client side matching if the user routes back up to `/parent`.
+    // This is the same thing we do on initial load in <Scripts> via
+    // `getPartialManifest()`
     for (let path of paths) {
       let matches = matchServerRoutes(routes, path, build.basename);
       if (matches) {

From 5cad5f8e66db8094d991f74510c74872af31832a Mon Sep 17 00:00:00 2001
From: Matt Brophy <matt@brophy.org>
Date: Tue, 23 Sep 2025 14:56:25 -0400
Subject: [PATCH 2/2] Handle new client/old server

---
 .../react-router/lib/dom/ssr/fog-of-war.ts    | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/packages/react-router/lib/dom/ssr/fog-of-war.ts b/packages/react-router/lib/dom/ssr/fog-of-war.ts
index 7541bd5383..c7c36eab7c 100644
--- a/packages/react-router/lib/dom/ssr/fog-of-war.ts
+++ b/packages/react-router/lib/dom/ssr/fog-of-war.ts
@@ -242,6 +242,25 @@ export async function fetchAndApplyManifestPatches(
   try {
     let res = await fetch(url, { signal });
 
+    // To avoid issues during rolling deployments if we get back a 400 when
+    // using `paths`, it's likely we hit an old server so retry the request
+    // with the old `p` parameters
+    if (res.status === 400) {
+      let body = await res.text();
+      if (body !== "Invalid Request") {
+        throw new Error(`${res.status} ${res.statusText}`);
+      }
+      const retrySearchParams = new URLSearchParams();
+      paths.sort().forEach((path) => retrySearchParams.append("p", path));
+      retrySearchParams.set("version", manifest.version);
+      let url = new URL(
+        getManifestPath(manifestPath, basename),
+        window.location.origin,
+      );
+      url.search = retrySearchParams.toString();
+      res = await fetch(url, { signal });
+    }
+
     if (!res.ok) {
       throw new Error(`${res.status} ${res.statusText}`);
     } else if (