fix(llmobs): handle Bedrock stream failures without chunks

## Summary

ConverseStream requests that fail before yielding data retain an empty assistant response instead of throwing from LLMObs.

## Why

An `iterator.next()` rejection publishes request completion without a streamed-chunk event, so `ctx.chunks` is undefined. Direct iteration then throws while handling the SDK failure.

## Test plan

`./node_modules/.bin/mocha packages/datadog-plugin-aws-sdk/test/bedrockruntime.util.spec.js` and `npm run lint`

Author: BridgeAR

packages/datadog-plugin-aws-sdk/src/services/bedrockruntime/utils.js

@@ -641,7 +641,7 @@ function extractTextAndResponseReasonConverse (response) {
  * response, spread across start/delta chunks. We reassemble those chunks
  * into a normalized content-block array and reuse the non-stream extractor.
  *
- * @param {Array<object>} chunks - Ordered ConverseStreamOutput events.
+ * @param {Array<object> | undefined} chunks - Ordered ConverseStreamOutput events.
  * @returns {Generation}
  */
 function extractTextAndResponseReasonConverseFromStream (chunks) {
@@ -650,29 +650,31 @@ function extractTextAndResponseReasonConverseFromStream (chunks) {
   let usage = {}
   const blocksByIdx = new Map()
 
-  for (const chunk of chunks) {
-    if (chunk.messageStart?.role) {
-      role = chunk.messageStart.role
-    } else if (chunk.messageStop?.stopReason) {
-      stopReason = chunk.messageStop.stopReason
-    } else if (chunk.metadata?.usage) {
-      usage = chunk.metadata.usage
-    } else if (chunk.contentBlockStart?.start?.toolUse) {
-      const { contentBlockIndex, start: { toolUse } } = chunk.contentBlockStart
-      blocksByIdx.set(contentBlockIndex, {
-        toolUse: { toolUseId: toolUse.toolUseId, name: toolUse.name, inputStr: '' },
-      })
-    } else if (chunk.contentBlockDelta) {
-      const { contentBlockIndex, delta } = chunk.contentBlockDelta
-      if (typeof delta?.text === 'string') {
-        const block = blocksByIdx.get(contentBlockIndex) ?? {}
-        block.text = (block.text ?? '') + delta.text
-        blocksByIdx.set(contentBlockIndex, block)
-      } else if (typeof delta?.toolUse?.input === 'string') {
-        const block = blocksByIdx.get(contentBlockIndex) ?? { toolUse: { inputStr: '' } }
-        block.toolUse ??= { inputStr: '' }
-        block.toolUse.inputStr += delta.toolUse.input
-        blocksByIdx.set(contentBlockIndex, block)
+  if (chunks) {
+    for (const chunk of chunks) {
+      if (chunk.messageStart?.role) {
+        role = chunk.messageStart.role
+      } else if (chunk.messageStop?.stopReason) {
+        stopReason = chunk.messageStop.stopReason
+      } else if (chunk.metadata?.usage) {
+        usage = chunk.metadata.usage
+      } else if (chunk.contentBlockStart?.start?.toolUse) {
+        const { contentBlockIndex, start: { toolUse } } = chunk.contentBlockStart
+        blocksByIdx.set(contentBlockIndex, {
+          toolUse: { toolUseId: toolUse.toolUseId, name: toolUse.name, inputStr: '' },
+        })
+      } else if (chunk.contentBlockDelta) {
+        const { contentBlockIndex, delta } = chunk.contentBlockDelta
+        if (typeof delta?.text === 'string') {
+          const block = blocksByIdx.get(contentBlockIndex) ?? {}
+          block.text = (block.text ?? '') + delta.text
+          blocksByIdx.set(contentBlockIndex, block)
+        } else if (typeof delta?.toolUse?.input === 'string') {
+          const block = blocksByIdx.get(contentBlockIndex) ?? { toolUse: { inputStr: '' } }
+          block.toolUse ??= { inputStr: '' }
+          block.toolUse.inputStr += delta.toolUse.input
+          blocksByIdx.set(contentBlockIndex, block)
+        }
       }
     }
   }

packages/datadog-plugin-aws-sdk/test/bedrockruntime.util.spec.js

@@ -9,6 +9,36 @@ const {
 } = require('../src/services/bedrockruntime/utils')
 
 describe('bedrockruntime converse stream extractor', () => {
+  it('returns an empty message when the stream fails before yielding a chunk', () => {
+    const generation = extractTextAndResponseReasonConverseFromStream()
+
+    assert.deepStrictEqual(generation.messages, [{ role: 'assistant', content: '' }])
+  })
+
+  it('aggregates streamed text, tool input, metadata, and the stop reason', () => {
+    const generation = extractTextAndResponseReasonConverseFromStream([
+      { messageStart: { role: 'assistant' } },
+      { contentBlockDelta: { contentBlockIndex: 0, delta: { text: 'hel' } } },
+      { contentBlockDelta: { contentBlockIndex: 0, delta: { text: 'lo' } } },
+      { contentBlockDelta: { contentBlockIndex: 1, delta: { toolUse: { input: '{"city":"Berlin"}' } } } },
+      { metadata: { usage: { inputTokens: 2, outputTokens: 3 } } },
+      { messageStop: { stopReason: 'tool_use' } },
+    ])
+
+    assert.deepStrictEqual(generation.messages, [{
+      role: 'assistant',
+      content: 'hello',
+      toolCalls: [{ name: '', arguments: { city: 'Berlin' }, toolId: '', type: 'toolUse' }],
+    }])
+    assert.deepStrictEqual(generation.usage, {
+      inputTokens: 2,
+      outputTokens: 3,
+      cacheReadTokens: undefined,
+      cacheWriteTokens: undefined,
+    })
+    assert.strictEqual(generation.finishReason, 'tool_use')
+  })
+
   it('emits empty tool-call arguments when the streamed tool-use input is malformed JSON', () => {
     const generation = extractTextAndResponseReasonConverseFromStream([
       { messageStart: { role: 'assistant' } },