Document async/await and Promise handling in Code Interpreter

Adds documentation for automatic Promise resolution in JavaScript and
TypeScript contexts. The Code Interpreter now properly awaits Promise
results, allowing async/await patterns to work correctly.

Includes examples for:
- Async IIFE patterns
- Direct Promise.resolve usage
- Nested async operations
- Async error handling with Promise.reject

References cloudflare/sandbox-sdk#246

Author: github-actions[bot]

src/content/docs/sandbox/api/interpreter.mdx

@@ -90,6 +90,45 @@ console.log(result.results[0].text); // "15"
 </TypeScriptExample>
 :::
 
+**Async/await and Promise handling (JavaScript and TypeScript)**:
+
+The Code Interpreter automatically awaits Promise results in JavaScript and TypeScript contexts, allowing you to work with async code naturally.
+
+<TypeScriptExample>
+```
+const ctx = await sandbox.createCodeContext({ language: 'javascript' });
+
+// Async IIFE
+const result1 = await sandbox.runCode(`
+(async () => {
+  const value = await Promise.resolve(42);
+  return { result: value * 2 };
+})()
+`, { context: ctx });
+
+console.log(result1.results[0].json); // { result: 84 }
+
+// Direct Promise.resolve
+const result2 = await sandbox.runCode(
+  'Promise.resolve({ status: "success" })',
+  { context: ctx }
+);
+
+console.log(result2.results[0].json); // { status: "success" }
+
+// Nested async operations
+const result3 = await sandbox.runCode(`
+(async () => {
+  const a = await Promise.resolve(10);
+  const b = await Promise.resolve(20);
+  return { sum: a + b };
+})()
+`, { context: ctx });
+
+console.log(result3.results[0].json); // { sum: 30 }
+```
+</TypeScriptExample>
+
 **Error handling**:
 
 <TypeScriptExample>
@@ -104,6 +143,21 @@ if (result.error) {
 ```
 </TypeScriptExample>
 
+**Async error handling**:
+
+<TypeScriptExample>
+```
+const result = await sandbox.runCode(
+  'Promise.reject(new Error("Async error"))',
+  { language: 'javascript' }
+);
+
+if (result.error) {
+  console.error(result.error.message); // "Async error"
+}
+```
+</TypeScriptExample>
+
 ### `listCodeContexts()`
 
 List all active code execution contexts.