docs(vercel): nested executions within parent trace

pages/docs/integrations/vercel-ai-sdk.mdx

@@ -174,21 +174,62 @@ We created a sample repository ([langfuse/langfuse-vercel-ai-nextjs-example](htt
 
 ## Customization
 
+### Group multiple executions in one trace
+
+You can open a Langfuse trace and pass the trace ID to AI SDK calls to group multiple execution spans under one trace. The passed name in functionId will be the root span name of the respective execution.
+
+```typescript
+import { randomUUID } from "crypto";
+import { Langfuse } from "langfuse";
+
+const langfuse = new Langfuse();
+const parentTraceId = randomUUID();
+
+langfuse.trace({
+  id: parentTraceId,
+  name: "holiday-traditions",
+});
+
+for (let i = 0; i < 3; i++) {
+  const result = await generateText({
+    model: openai("gpt-3.5-turbo"),
+    maxTokens: 50,
+    prompt: "Invent a new holiday and describe its traditions.",
+    experimental_telemetry: {
+      isEnabled: true,
+      functionId: `holiday-tradition-${i}`,
+      metadata: {
+        langfuseTraceId: parentTraceId,
+      },
+    },
+  });
+
+  console.log(result.text);
+}
+
+await langfuse.flushAsync();
+await sdk.shutdown();
+```
+
+The resulting trace hierarchy will be:
+
+![Vercel nested trace in Langfuse UI](/images/docs/vercel-nested-trace.png)
+
 ### Disable Tracking of Input/Output
 
 By default, the exporter captures the input and output of each request. You can disable this behavior by setting the `recordInputs` and `recordOutputs` options to `false`.
 
 ### Link Langfuse prompts to traces
 
-You can link Langfuse prompts to Vercel AI SDK generations by setting the `langfusePrompt` property in the `metadata` field: 
+You can link Langfuse prompts to Vercel AI SDK generations by setting the `langfusePrompt` property in the `metadata` field:
 
 ```typescript
-import { generateText } from "ai"
-import { Langfuse } from "langfuse"
+import { generateText } from "ai";
+import { Langfuse } from "langfuse";
 
-const langfuse = new Langfuse()
+const langfuse = new Langfuse();
 
-const fetchedPrompt = await langfuse.getPrompt('my-prompt')
+const fetchedPrompt = await langfuse.getPrompt("my-prompt");
 
 const result = await generateText({
   model: openai("gpt-4o"),
@@ -243,6 +284,10 @@ new LangfuseExporter({ debug: true });
   - set `skipOpenTelemetrySetup: true` in Sentry.init
   - follow Sentry's docs on how to manually set up Sentry with OTEL
 
+### Short-lived environments
+
+In short-lived environments such as Vercel Cloud Functions, AWS Lambdas etc. you may force an export and flushing of spans after function execution and prior to environment freeze or shutdown by awaiting a call to the `forceFlush` method on the LangfuseExporter instance.
+
 ## Learn more
 
 See the [telemetry documentation](https://sdk.vercel.ai/docs/ai-sdk-core/telemetry) of the Vercel AI SDK for more information.