Fix #4168: Support Claude V3 response format in DefaultLLMImpl

[sonianuj287]

This PR updates the DefaultLlmImpl class to properly parse responses from the Claude V3 family of Bedrock models. Previously, only the V2 response format (completion field) was supported. With this change, the parser now supports the V3 format (content -> text) while maintaining backward compatibility with V2.

Changes Made

• Updated buildChatCompletionOutput():
  Detects "content" field for Claude V3 responses.
  Extracts text from the first element of the content list.
  Adds extracted text to answers.
  Added a new unit test in DefaultLlmImplTests.java:
• testChatCompletionApiForBedrockClaudeV3()
  Mocks a V3-style Bedrock response and validates output parsing.
  Reformatted test files to satisfy Spotless formatting rules.

Why this change is needed
Claude V2 models are deprecated; V3 is the current standard.
Without this fix, requests to "bedrock/anthropic-claude" with V3 models fail to extract answers, causing RAG pipelines to break.
Ensures users don’t need to pass llmResponseField manually for default Bedrock Claude models.

How to test
Run all existing unit tests:
./gradlew clean build

resolves #4168 (comment)

[sonianuj287]

Hi @mingshl @rithin-pullela-aws , Could you please review my PR and suggest changes.

Thanks :)

[mingshl]

oh great, this is going to use the same interface string, and it will auto detect these two formats and parse accordingly. Can you also add in ITs? this is the best way we can monitor and keep track when the model interface failed.

I ran your CIs and also I added the resolved issues and link the issue in the PR descriptions.

[ylwu-amzn]

rebased with latest main branch

[ylwu-amzn]

Can you add some test REST API examples to the description? Like how to create model, how to create pipeline and how to run it. So other reviews can understand more clearly.

[mingshl]

can you try remove the response filter in this IT and see if this IT still pass?

ml-commons/plugin/src/test/java/org/opensearch/ml/rest/RestMLRAGSearchProcessorIT.java

Line 127 in da23d19

+ "\"response_filter\": \"$.content[0].text\""

this response filter was added to force the new interface is working. hopefully after this PR, we don't need changing the connectors.

[sonianuj287]

Hi @ylwu-amzn , I can see some test cases failed and your code changes. Let me know my further steps, what actions should I take.
I can take a look for test case fixing, if so anything to keep focus on..

[sonianuj287]

Can you add some test REST API examples to the description? Like how to create model, how to create pipeline and how to run it. So other reviews can understand more clearly.

Yes, will do that

[sonianuj287]

can you try remove the response filter in this IT and see if this IT still pass?

ml-commons/plugin/src/test/java/org/opensearch/ml/rest/RestMLRAGSearchProcessorIT.java

Line 127 in da23d19

+ "\"response_filter\": \"$.content[0].text\""

this response filter was added to force the new interface is working. hopefully after this PR, we don't need changing the connectors.

Thanks for pointing this. surely will do