feat: add llm obs patch (#7449)

* add llm obs patch

* add staging vars

letta/server/rest_api/app.py

@@ -241,10 +241,6 @@ def create_application() -> "FastAPI":
             os.environ.setdefault("DD_PROFILING_MEMORY_ENABLED", str(telemetry_settings.datadog_profiling_memory_enabled).lower())
             os.environ.setdefault("DD_PROFILING_HEAP_ENABLED", str(telemetry_settings.datadog_profiling_heap_enabled).lower())
 
-            # Enable LLM Observability for tracking LLM calls, prompts, and completions
-            os.environ.setdefault("DD_LLMOBS_ENABLED", "1")
-            os.environ.setdefault("DD_LLMOBS_ML_APP", "memgpt-server")
-
             # Note: DD_LOGS_INJECTION, DD_APPSEC_ENABLED, DD_IAST_ENABLED, DD_APPSEC_SCA_ENABLED
             # are set via deployment configs and automatically picked up by ddtrace
 
@@ -252,6 +248,15 @@ def create_application() -> "FastAPI":
             import ddtrace
 
             ddtrace.patch_all()  # Auto-instrument FastAPI, HTTP, DB, etc.
+
+            llmobs_flag = os.getenv("DD_LLMOBS_ENABLED", "")
+            from ddtrace.llmobs import LLMObs
+
+            if llmobs_flag:
+                LLMObs.enable(
+                    ml_app=os.getenv("DD_LLMOBS_ML_APP") or telemetry_settings.datadog_service_name,
+                )
+
             logger.info(
                 f"Datadog tracer initialized: env={dd_env}, "
                 f"service={telemetry_settings.datadog_service_name}, "