Metadata Loss in DefaultChatClient.DefaultStreamResponseSpec When Converting UserMessage to AdvisedRequest

[ck-jesse]

Bug description

Metadata from UserMessage is inadvertently discarded during the conversion chain in streaming responses. Key breakdown:

Data Loss Point:
DefaultStreamResponseSpec.doGetObservableFluxChatResponse loses metadata when calling toAdvisedRequest.
StreamAroundAdvisor’s internal AdvisedRequest.toPrompt() fails to propagate metadata.

Environment
Spring AI version: 1.0.0-M6
Affected module: spring-ai-core

Expected behavior
UserMessage metadata should persist through the entire processing chain for multimodal support.

[ThomasVitale]

@ck-jesse thanks for raising this issue. It should have been fixed in M8, where a complete Prompt object is propagated throughout the advisor chain instead of the approach used before that was leading to metadata loss for user and system messages. Can you confirm that's the case?