feat: add langfuse metadata and tags

Author: stevenbdf

fern/providers/observability/langfuse.mdx

@@ -76,3 +76,39 @@ To make the most out of this integration, you can now use Langfuse's [evaluation
 
 </Step>
 </Steps>
+
+## Enrich Traces
+Vapi allows you to enrich Langfuse traces by integrating [Metadata](https://langfuse.com/docs/tracing-features/metadata) and [Tags](https://langfuse.com/docs/tracing-features/tags).
+
+By default, we will add the following values to the metadata of each trace:
+
+- `call.metadata`
+- `assistant.metadata`
+- `assistantOverrides.metadata`
+- `assistantOverrides.variableValues`
+
+### Usage
+You can enhance your observability in Langfuse by adding metadata and tags:
+
+**Metadata**
+
+Use the [`assistant.observabilityPlan.metadata`](https://docs.vapi.ai/api-reference/assistants/create#request.body.observabilityPlan.metadata) field to attach custom key-value pairs.
+
+Examples:
+- Track experiment versions ("experiment": "v2.1")
+- Store user segments ("user_type": "beta_tester")
+- Log environment details ("env": "production")
+
+**Tags**
+
+Use the [`assistant.observabilityPlan.tags`](https://docs.vapi.ai/api-reference/assistants/create#request.body.observabilityPlan.tags) field to add searchable labels.
+
+Examples:
+- Mark important runs ("priority")
+- Group related sessions ("onboarding", "A/B_test")
+- Filter by feature ("voice_assistant")
+
+Adding metadata and tags makes it easier to filter, analyze, and monitor your assistants activity in Langfuse.
+
+### Example
+![Langfuse Metadata Example](../../static/images/providers/langfuse-example.png)