fix(chat): handle multiple returnDirect responses in DefaultChatClient (#4655)

[kuntal1461]

Summary

This PR fixes an issue where ChatClient.content() returned only the first generation when multiple tools used returnDirect = true.
The update ensures that all returnDirect generations are aggregated consistently across both call() and stream() flows, independent of the provider implementation.

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Changes

File updated:
spring-ai-client-chat/src/main/java/org/springframework/ai/chat/client/DefaultChatClient.java

• getContentFromChatResponse (around L525):

  • Single generation: Behavior unchanged.
  • Multiple generations with finishReason = "returnDirect":
    → Concatenate all generation texts using a newline (\n).
  • Otherwise: Fall back to the first generation (existing behavior).

• stream().content() aggregation logic:
  Updated to mirror the same multi-generation handling for consistency with synchronous responses.

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Tests

New test class:
spring-ai-client-chat/src/test/java/org/springframework/ai/chat/client/DefaultChatClientReturnDirectAggregationTests.java

• aggregatesMultipleReturnDirectGenerationsInContent:
  Verifies that multiple returnDirect generations are joined with newlines.
• returnsFirstWhenNotAllReturnDirect:
  Ensures fallback to the first generation when not all generations use returnDirect.

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Compatibility

✅ No breaking changes.

• Behavior remains identical when:

  • There is only one generation, or
  • Not all generations are marked returnDirect.

This enhancement improves content consistency and tool aggregation behavior without altering existing APIs.

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Notes

• Ensures unified aggregation logic across both call() and stream() methods.
• Keeps provider implementations untouched and fully backward-compatible.