refactor(router-plugin): upgrade unplugin to v3

.changeset/fuzzy-carpets-enter.md

@@ -0,0 +1,5 @@
+---
+'@tanstack/start-client-core': patch
+---
+
+refactor(start-client-core): use a more explicit typing to `CustomFetch` type

.changeset/loud-tigers-crash.md

@@ -0,0 +1,5 @@
+---
+'@tanstack/router-plugin': patch
+---
+
+refactor(router-plugin): upgrade unplugin to `v3`

examples/solid/start-convex-better-auth/src/library/convex-client.ts

@@ -3,7 +3,7 @@ import { fetchAuth } from '~/library/server'
 
 const CONVEX_URL = import.meta.env.VITE_CONVEX_URL
 if (!CONVEX_URL) {
-  console.error('missing envar CONVEX_URL')
+  throw new Error('missing envar CONVEX_URL')
 }
 
 // Set up Convex client with auth

packages/router-plugin/package.json

@@ -118,7 +118,7 @@
     "@tanstack/router-utils": "workspace:*",
     "@tanstack/virtual-file-routes": "workspace:*",
     "chokidar": "^3.6.0",
-    "unplugin": "^2.1.2",
+    "unplugin": "^3.0.0",
     "zod": "^3.24.2"
   },
   "devDependencies": {

packages/start-client-core/src/createServerFn.ts

@@ -380,7 +380,13 @@ export interface RequiredFetcher<
   ): Promise<Awaited<TResponse>>
 }
 
-export type CustomFetch = typeof globalThis.fetch
+// Ideally, this type should just be `export type CustomFetch = typeof globalThis.fetch`, but that conflicts with the type overrides the `bun-types` package - a dependency of unplugin.
+// Relevant bun issues:
+// - https://github.com/oven-sh/bun/issues/23500
+// - https://github.com/oven-sh/bun/issues/23741
+export type CustomFetch = typeof fetch extends (...args: infer A) => infer R
+  ? (...args: A) => R
+  : never
 
 export type FetcherBaseOptions = {
   headers?: HeadersInit