[MLOB-2096] feat(llmobs): metadata and metrics annotations update instead of override (#5243)

* update don't override

* remove unecessary changes

Author: sabrenner

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

@@ -100,7 +100,12 @@ class LLMObsTagger {
   }
 
   tagMetadata (span, metadata) {
-    this._setTag(span, METADATA, metadata)
+    const existingMetadata = registry.get(span)?.[METADATA]
+    if (existingMetadata) {
+      Object.assign(existingMetadata, metadata)
+    } else {
+      this._setTag(span, METADATA, metadata)
+    }
   }
 
   tagMetrics (span, metrics) {
@@ -128,7 +133,12 @@ class LLMObsTagger {
       }
     }
 
-    this._setTag(span, METRICS, filterdMetrics)
+    const existingMetrics = registry.get(span)?.[METRICS]
+    if (existingMetrics) {
+      Object.assign(existingMetrics, filterdMetrics)
+    } else {
+      this._setTag(span, METRICS, filterdMetrics)
+    }
   }
 
   tagSpanTags (span, tags) {

packages/dd-trace/test/llmobs/tagger.spec.js

@@ -168,6 +168,14 @@ describe('tagger', () => {
           '_ml_obs.meta.metadata': { a: 'foo', b: 'bar' }
         })
       })
+
+      it('updates instead of overriding', () => {
+        Tagger.tagMap.set(span, { '_ml_obs.meta.metadata': { a: 'foo' } })
+        tagger.tagMetadata(span, { b: 'bar' })
+        expect(Tagger.tagMap.get(span)).to.deep.equal({
+          '_ml_obs.meta.metadata': { a: 'foo', b: 'bar' }
+        })
+      })
     })
 
     describe('tagMetrics', () => {
@@ -202,6 +210,14 @@ describe('tagger', () => {
         tagger._register(span)
         expect(() => tagger.tagMetrics(span, metrics)).to.throw()
       })
+
+      it('updates instead of overriding', () => {
+        Tagger.tagMap.set(span, { '_ml_obs.metrics': { a: 1 } })
+        tagger.tagMetrics(span, { b: 2 })
+        expect(Tagger.tagMap.get(span)).to.deep.equal({
+          '_ml_obs.metrics': { a: 1, b: 2 }
+        })
+      })
     })
 
     describe('tagSpanTags', () => {