diff --git a/.changeset/tame-islands-play.md b/.changeset/tame-islands-play.md
new file mode 100644
index 00000000000..40588c17eee
--- /dev/null
+++ b/.changeset/tame-islands-play.md
@@ -0,0 +1,6 @@
+---
+'@tanstack/start-client-core': patch
+'@tanstack/start-server-core': patch
+---
+
+Ensure request middleware context wins over colliding client-provided context in server function execution paths, including SSR, GET, and FormData requests.
diff --git a/e2e/react-start/server-functions-global-middleware/src/routeTree.gen.ts b/e2e/react-start/server-functions-global-middleware/src/routeTree.gen.ts
index 425fc58a24c..6fb74e28a27 100644
--- a/e2e/react-start/server-functions-global-middleware/src/routeTree.gen.ts
+++ b/e2e/react-start/server-functions-global-middleware/src/routeTree.gen.ts
@@ -12,6 +12,7 @@ import { Route as rootRouteImport } from './routes/__root'
 import { Route as SimpleRouteImport } from './routes/simple'
 import { Route as PathnameMiddlewareRouteImport } from './routes/pathname-middleware'
 import { Route as MultipleServerFunctionsRouteImport } from './routes/multiple-server-functions'
+import { Route as ContextCollisionRouteImport } from './routes/context-collision'
 import { Route as IndexRouteImport } from './routes/index'
 
 const SimpleRoute = SimpleRouteImport.update({
@@ -29,6 +30,11 @@ const MultipleServerFunctionsRoute = MultipleServerFunctionsRouteImport.update({
   path: '/multiple-server-functions',
   getParentRoute: () => rootRouteImport,
 } as any)
+const ContextCollisionRoute = ContextCollisionRouteImport.update({
+  id: '/context-collision',
+  path: '/context-collision',
+  getParentRoute: () => rootRouteImport,
+} as any)
 const IndexRoute = IndexRouteImport.update({
   id: '/',
   path: '/',
@@ -37,12 +43,14 @@ const IndexRoute = IndexRouteImport.update({
 
 export interface FileRoutesByFullPath {
   '/': typeof IndexRoute
+  '/context-collision': typeof ContextCollisionRoute
   '/multiple-server-functions': typeof MultipleServerFunctionsRoute
   '/pathname-middleware': typeof PathnameMiddlewareRoute
   '/simple': typeof SimpleRoute
 }
 export interface FileRoutesByTo {
   '/': typeof IndexRoute
+  '/context-collision': typeof ContextCollisionRoute
   '/multiple-server-functions': typeof MultipleServerFunctionsRoute
   '/pathname-middleware': typeof PathnameMiddlewareRoute
   '/simple': typeof SimpleRoute
@@ -50,6 +58,7 @@ export interface FileRoutesByTo {
 export interface FileRoutesById {
   __root__: typeof rootRouteImport
   '/': typeof IndexRoute
+  '/context-collision': typeof ContextCollisionRoute
   '/multiple-server-functions': typeof MultipleServerFunctionsRoute
   '/pathname-middleware': typeof PathnameMiddlewareRoute
   '/simple': typeof SimpleRoute
@@ -58,14 +67,21 @@ export interface FileRouteTypes {
   fileRoutesByFullPath: FileRoutesByFullPath
   fullPaths:
     | '/'
+    | '/context-collision'
     | '/multiple-server-functions'
     | '/pathname-middleware'
     | '/simple'
   fileRoutesByTo: FileRoutesByTo
-  to: '/' | '/multiple-server-functions' | '/pathname-middleware' | '/simple'
+  to:
+    | '/'
+    | '/context-collision'
+    | '/multiple-server-functions'
+    | '/pathname-middleware'
+    | '/simple'
   id:
     | '__root__'
     | '/'
+    | '/context-collision'
     | '/multiple-server-functions'
     | '/pathname-middleware'
     | '/simple'
@@ -73,6 +89,7 @@ export interface FileRouteTypes {
 }
 export interface RootRouteChildren {
   IndexRoute: typeof IndexRoute
+  ContextCollisionRoute: typeof ContextCollisionRoute
   MultipleServerFunctionsRoute: typeof MultipleServerFunctionsRoute
   PathnameMiddlewareRoute: typeof PathnameMiddlewareRoute
   SimpleRoute: typeof SimpleRoute
@@ -101,6 +118,13 @@ declare module '@tanstack/react-router' {
       preLoaderRoute: typeof MultipleServerFunctionsRouteImport
       parentRoute: typeof rootRouteImport
     }
+    '/context-collision': {
+      id: '/context-collision'
+      path: '/context-collision'
+      fullPath: '/context-collision'
+      preLoaderRoute: typeof ContextCollisionRouteImport
+      parentRoute: typeof rootRouteImport
+    }
     '/': {
       id: '/'
       path: '/'
@@ -113,6 +137,7 @@ declare module '@tanstack/react-router' {
 
 const rootRouteChildren: RootRouteChildren = {
   IndexRoute: IndexRoute,
+  ContextCollisionRoute: ContextCollisionRoute,
   MultipleServerFunctionsRoute: MultipleServerFunctionsRoute,
   PathnameMiddlewareRoute: PathnameMiddlewareRoute,
   SimpleRoute: SimpleRoute,
diff --git a/e2e/react-start/server-functions-global-middleware/src/routes/context-collision.tsx b/e2e/react-start/server-functions-global-middleware/src/routes/context-collision.tsx
new file mode 100644
index 00000000000..e744e15d8a0
--- /dev/null
+++ b/e2e/react-start/server-functions-global-middleware/src/routes/context-collision.tsx
@@ -0,0 +1,155 @@
+import { createFileRoute } from '@tanstack/react-router'
+import { createMiddleware, createServerFn } from '@tanstack/react-start'
+import { useState } from 'react'
+
+const collisionMiddleware = createMiddleware({ type: 'function' }).client(
+  async ({ next }) => {
+    return next({
+      sendContext: {
+        trustedUser: 'client-user',
+        clientNonce: 'client-nonce',
+      },
+    })
+  },
+)
+
+const getCollisionContext = createServerFn()
+  .middleware([collisionMiddleware])
+  .handler(({ context }) => {
+    return {
+      trustedUser: context.trustedUser,
+      clientNonce: context.clientNonce,
+    }
+  })
+
+const postCollisionContext = createServerFn({ method: 'POST' })
+  .middleware([collisionMiddleware])
+  .inputValidator((data: unknown) => {
+    if (!(data instanceof FormData)) {
+      throw new Error('Expected FormData')
+    }
+
+    return {
+      attempt: String(data.get('attempt') ?? ''),
+    }
+  })
+  .handler(({ context, data }) => {
+    return {
+      trustedUser: context.trustedUser,
+      clientNonce: context.clientNonce,
+      attempt: data.attempt,
+    }
+  })
+
+type CollisionResult = {
+  trustedUser: string | undefined
+  clientNonce: string | undefined
+}
+
+export const Route = createFileRoute('/context-collision')({
+  loader: async () => {
+    return {
+      loaderResult: await getCollisionContext(),
+    }
+  },
+  component: ContextCollisionComponent,
+})
+
+function ContextCollisionResult({
+  label,
+  result,
+  testIdPrefix,
+}: {
+  label: string
+  result: CollisionResult | null
+  testIdPrefix: string
+}) {
+  const status =
+    result &&
+    result.trustedUser === 'server-user' &&
+    result.clientNonce === 'client-nonce'
+      ? 'PASS'
+      : 'FAIL'
+
+  return (
+    <div className="mb-4">
+      <h2 className="font-semibold">{label}</h2>
+      <div>
+        trustedUser:{' '}
+        <span data-testid={`${testIdPrefix}-trusted-user`}>
+          {result?.trustedUser ?? 'pending'}
+        </span>
+      </div>
+      <div>
+        clientNonce:{' '}
+        <span data-testid={`${testIdPrefix}-client-nonce`}>
+          {result?.clientNonce ?? 'pending'}
+        </span>
+      </div>
+      <div data-testid={`${testIdPrefix}-status`}>{status}</div>
+    </div>
+  )
+}
+
+function ContextCollisionComponent() {
+  const { loaderResult } = Route.useLoaderData()
+  const [getResult, setGetResult] = useState<CollisionResult | null>(null)
+  const [postResult, setPostResult] = useState<CollisionResult | null>(null)
+
+  return (
+    <div className="p-8">
+      <h1 className="font-bold text-lg mb-4">
+        Client Context Collision Regression
+      </h1>
+
+      <p className="mb-4 text-gray-600">
+        Trusted request middleware context should win over colliding client
+        sendContext keys while preserving non-colliding client context.
+      </p>
+
+      <ContextCollisionResult
+        label="SSR loader result"
+        result={loaderResult}
+        testIdPrefix="loader"
+      />
+
+      <div className="mb-4 flex gap-4">
+        <button
+          data-testid="invoke-get-collision"
+          type="button"
+          className="rounded-md bg-white px-2.5 py-1.5 text-sm font-semibold text-gray-900 shadow-xs ring-1 ring-inset ring-gray-300 hover:bg-gray-50"
+          onClick={async () => {
+            setGetResult(await getCollisionContext())
+          }}
+        >
+          Call GET server function
+        </button>
+
+        <button
+          data-testid="invoke-post-collision"
+          type="button"
+          className="rounded-md bg-white px-2.5 py-1.5 text-sm font-semibold text-gray-900 shadow-xs ring-1 ring-inset ring-gray-300 hover:bg-gray-50"
+          onClick={async () => {
+            const formData = new FormData()
+            formData.set('attempt', 'formdata')
+            setPostResult(await postCollisionContext({ data: formData }))
+          }}
+        >
+          Call POST server function
+        </button>
+      </div>
+
+      <ContextCollisionResult
+        label="Client GET result"
+        result={getResult}
+        testIdPrefix="get"
+      />
+
+      <ContextCollisionResult
+        label="Client FormData POST result"
+        result={postResult}
+        testIdPrefix="post"
+      />
+    </div>
+  )
+}
diff --git a/e2e/react-start/server-functions-global-middleware/src/start.ts b/e2e/react-start/server-functions-global-middleware/src/start.ts
index 7d22827605a..a6b89d7f7d1 100644
--- a/e2e/react-start/server-functions-global-middleware/src/start.ts
+++ b/e2e/react-start/server-functions-global-middleware/src/start.ts
@@ -61,6 +61,16 @@ export const pathnameMiddleware = createMiddleware().server(
   },
 )
 
+export const trustedUserMiddleware = createMiddleware().server(
+  async ({ next }) => {
+    return next({
+      context: {
+        trustedUser: 'server-user',
+      },
+    })
+  },
+)
+
 // Global function middleware that should be deduped across server functions
 export const globalFunctionMiddleware = createMiddleware({
   type: 'function',
@@ -91,5 +101,9 @@ export const startInstance = createStart(() => ({
   functionMiddleware: [globalFunctionMiddleware, globalFunctionMiddleware2],
   // Request middleware - includes loggingMiddleware (issue #5239 scenario)
   // AND the same loggingMiddleware is also attached to server functions
-  requestMiddleware: [loggingMiddleware, pathnameMiddleware],
+  requestMiddleware: [
+    trustedUserMiddleware,
+    loggingMiddleware,
+    pathnameMiddleware,
+  ],
 }))
diff --git a/e2e/react-start/server-functions-global-middleware/tests/global-middleware.spec.ts b/e2e/react-start/server-functions-global-middleware/tests/global-middleware.spec.ts
index 211d7f59c79..3b1eac10813 100644
--- a/e2e/react-start/server-functions-global-middleware/tests/global-middleware.spec.ts
+++ b/e2e/react-start/server-functions-global-middleware/tests/global-middleware.spec.ts
@@ -153,3 +153,36 @@ test.describe('Request middleware pathname (issue #6647)', () => {
     expect(pathnameText!.startsWith('/_serverFn/')).toBe(true)
   })
 })
+
+test.describe('Client sendContext collisions (TSR-003)', () => {
+  test('trusted server middleware context wins for SSR, GET, and FormData calls', async ({
+    page,
+  }) => {
+    await page.goto('/context-collision')
+    await page.waitForLoadState('networkidle')
+
+    await expect(page.getByTestId('loader-status')).toHaveText('PASS')
+    await expect(page.getByTestId('loader-trusted-user')).toHaveText(
+      'server-user',
+    )
+    await expect(page.getByTestId('loader-client-nonce')).toHaveText(
+      'client-nonce',
+    )
+
+    await page.getByTestId('invoke-get-collision').click()
+    await expect(page.getByTestId('get-status')).toHaveText('PASS')
+    await expect(page.getByTestId('get-trusted-user')).toHaveText('server-user')
+    await expect(page.getByTestId('get-client-nonce')).toHaveText(
+      'client-nonce',
+    )
+
+    await page.getByTestId('invoke-post-collision').click()
+    await expect(page.getByTestId('post-status')).toHaveText('PASS')
+    await expect(page.getByTestId('post-trusted-user')).toHaveText(
+      'server-user',
+    )
+    await expect(page.getByTestId('post-client-nonce')).toHaveText(
+      'client-nonce',
+    )
+  })
+})
diff --git a/packages/start-client-core/src/createServerFn.ts b/packages/start-client-core/src/createServerFn.ts
index 42eef35aec2..a4d0c71b829 100644
--- a/packages/start-client-core/src/createServerFn.ts
+++ b/packages/start-client-core/src/createServerFn.ts
@@ -152,7 +152,6 @@ export const createServerFn: CreateServerFn<Register> = (options, __opts) => {
             const startContext = getStartContextServerOnly()
             const serverContextAfterGlobalMiddlewares =
               startContext.contextAfterGlobalMiddlewares
-            // Use safeObjectMerge for opts.context which comes from client
             const ctx = {
               ...extractedFn,
               ...opts,
@@ -160,10 +159,10 @@ export const createServerFn: CreateServerFn<Register> = (options, __opts) => {
               // (which has id, name, filename) rather than the partial one from SSR/client
               // callers (which only has id)
               serverFnMeta: extractedFn.serverFnMeta,
-              // Use safeObjectMerge for opts.context which comes from client
+              // Merge client context first so trusted server middleware context wins.
               context: safeObjectMerge(
-                serverContextAfterGlobalMiddlewares,
                 opts.context,
+                serverContextAfterGlobalMiddlewares,
               ),
               request: startContext.request,
             }
diff --git a/packages/start-server-core/src/server-functions-handler.ts b/packages/start-server-core/src/server-functions-handler.ts
index 7b3b34585be..ff047ec0397 100644
--- a/packages/start-server-core/src/server-functions-handler.ts
+++ b/packages/start-server-core/src/server-functions-handler.ts
@@ -117,8 +117,8 @@ export const handleServerAction = async ({
                 deserializedContext
               ) {
                 params.context = safeObjectMerge(
-                  context,
                   deserializedContext as Record<string, unknown>,
+                  context,
                 )
               }
             } catch (e) {
@@ -144,7 +144,7 @@ export const handleServerAction = async ({
           const payload: any = payloadParam
             ? parsePayload(JSON.parse(payloadParam))
             : {}
-          payload.context = safeObjectMerge(context, payload.context)
+          payload.context = safeObjectMerge(payload.context, context)
           payload.method = methodUpper
           // Send it through!
           return await action(payload)