From 9608c2c030d2fe60dff882b774d762a0c3ca7a7f Mon Sep 17 00:00:00 2001
From: Manuel Schiller <manuel.schiller@caligano.de>
Date: Wed, 29 Apr 2026 21:48:35 +0200
Subject: [PATCH 1/2] fix: disabled topLevelVar

this will cause isServer not to be transpiled to `var` and thus rspack can properly DCE
---
 .changeset/slow-seahorses-grab.md   | 5 +++++
 packages/router-core/vite.config.ts | 7 +++++++
 2 files changed, 12 insertions(+)
 create mode 100644 .changeset/slow-seahorses-grab.md

diff --git a/.changeset/slow-seahorses-grab.md b/.changeset/slow-seahorses-grab.md
new file mode 100644
index 00000000000..aa269d75978
--- /dev/null
+++ b/.changeset/slow-seahorses-grab.md
@@ -0,0 +1,5 @@
+---
+'@tanstack/router-core': patch
+---
+
+prevent isServer exports from being transformed to top-level vars so rspack can dead-code eliminate them
diff --git a/packages/router-core/vite.config.ts b/packages/router-core/vite.config.ts
index 816b0602b87..9fa5d5d736c 100644
--- a/packages/router-core/vite.config.ts
+++ b/packages/router-core/vite.config.ts
@@ -7,6 +7,13 @@ import type { ViteUserConfig } from 'vitest/config'
 
 const config = defineConfig({
   plugins: [minifyScriptPlugin()] as ViteUserConfig['plugins'],
+  build: {
+    rolldownOptions: {
+      output: {
+        topLevelVar: false
+      }
+    }
+  },
   test: {
     name: packageJson.name,
     dir: './tests',

From 5b47836c61bd6731aadc8660faae6a139884b2e5 Mon Sep 17 00:00:00 2001
From: "autofix-ci[bot]" <114827586+autofix-ci[bot]@users.noreply.github.com>
Date: Wed, 29 Apr 2026 19:52:31 +0000
Subject: [PATCH 2/2] ci: apply automated fixes

---
 packages/router-core/vite.config.ts | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/packages/router-core/vite.config.ts b/packages/router-core/vite.config.ts
index 9fa5d5d736c..413c56c4045 100644
--- a/packages/router-core/vite.config.ts
+++ b/packages/router-core/vite.config.ts
@@ -10,9 +10,9 @@ const config = defineConfig({
   build: {
     rolldownOptions: {
       output: {
-        topLevelVar: false
-      }
-    }
+        topLevelVar: false,
+      },
+    },
   },
   test: {
     name: packageJson.name,