feat(llmobs): add source:otel tag to evaluations when DD_TRACE_OTEL_ENABLED is set (#7113)

* feat:

* Sam comments

Author: ZStriker19

packages/dd-trace/src/llmobs/sdk.js

@@ -410,6 +410,11 @@ class LLMObs extends NoopLLMObs {
         }
       }
 
+      // When OTel tracing is enabled, add source:otel tag to allow backend to wait for OTel span conversion
+      if (isTrue(getEnvironmentVariable('DD_TRACE_OTEL_ENABLED'))) {
+        evaluationTags.source = 'otel'
+      }
+
       const payload = {
         span_id: spanId,
         trace_id: traceId,

packages/dd-trace/test/llmobs/sdk/index.spec.js

@@ -1258,6 +1258,29 @@ describe('sdk', () => {
         value: 'it is super toxic!'
       }), { message: 'value must be a boolean for a boolean metric' })
     })
+
+    describe('with DD_TRACE_OTEL_ENABLED set', () => {
+      before(() => {
+        process.env.DD_TRACE_OTEL_ENABLED = 'true'
+      })
+
+      after(() => {
+        delete process.env.DD_TRACE_OTEL_ENABLED
+      })
+
+      it('adds source:otel tag', () => {
+        llmobs.submitEvaluation(spanCtx, {
+          mlApp: 'test',
+          timestampMs: 1234,
+          label: 'test',
+          metricType: 'score',
+          value: 0.6
+        })
+
+        const evalMetric = LLMObsEvalMetricsWriter.prototype.append.getCall(0).args[0]
+        assert.ok(evalMetric.tags.includes('source:otel'), 'Expected source:otel tag to be present')
+      })
+    })
   })
 
   describe('flush', () => {