fix(node): Preserve synchronous return behavior for streamText and other methods for AI (#17580)

Vercel AI integration was incorrectly wrapping all patched methods in an
async function, causing synchronous methods like streamText to return
Promises when they should return synchronous objects.

```
// Before
const result = streamText({model: "gpt-5"});
console.log(result); 
```

```
// After
const result = streamText({model: "gpt-5"});
console.log(result); // DefaultStreamTextResult { ... } ✅
```

Resolves: #17553

Author: RulaKhaled

packages/node/src/integrations/tracing/vercelai/instrumentation.ts

@@ -9,6 +9,7 @@ import {
   getActiveSpan,
   getCurrentScope,
   handleCallbackErrors,
+  isThenable,
   SDK_VERSION,
   withScope,
 } from '@sentry/core';
@@ -71,7 +72,7 @@ function isToolError(obj: unknown): obj is ToolError {
  * Check for tool errors in the result and capture them
  * Tool errors are not rejected in Vercel V5, it is added as metadata to the result content
  */
-function checkResultForToolErrors(result: unknown | Promise<unknown>): void {
+function checkResultForToolErrors(result: unknown): void {
   if (typeof result !== 'object' || result === null || !('content' in result)) {
     return;
   }
@@ -236,13 +237,18 @@ export class SentryVercelAiInstrumentation extends InstrumentationBase {
         };
 
         return handleCallbackErrors(
-          async () => {
+          () => {
             // @ts-expect-error we know that the method exists
-            const result = await originalMethod.apply(this, args);
+            const result = originalMethod.apply(this, args);
 
-            // Tool errors are not rejected in Vercel V5, it is added as metadata to the result content
-            checkResultForToolErrors(result);
+            if (isThenable(result)) {
+              // check for tool errors when the promise resolves, keep the original promise identity
+              result.then(checkResultForToolErrors, () => {});
+              return result;
+            }
 
+            // check for tool errors when the result is synchronous
+            checkResultForToolErrors(result);
             return result;
           },
           error => {