fix: separate content across streaming tool turns

[arnabnandy7]

Summary

Preserves native reasoning across streaming tool-call turns and prevents content from adjacent inference turns being merged into a single line.

This completes the native-thinking follow-up identified during #1826.

Fixes #1860.

Problem

The streaming tool loop flattened content from consecutive inference turns into a single Flux<String>.

This caused two related problems:

1. If a tool-requesting turn ended without a newline, its final reasoning content was joined to the first chunk after tool execution:

reasoning before tool<think>reasoning after tool

2. Spring AI identifies Anthropic native-thinking chunks using metadata["thinking"] = true, but the adapter converted every chunk into an ordinary LlmInferenceStreamEvent.Content. The text remained visible, but its native-thinking identity was lost.

Changes

• Add provider-neutral LlmInferenceStreamEvent.Thinking.
• Map Spring AI native-thinking metadata to the new event type.
• Preserve native-thinking identity across tool execution and subsequent inference turns.
• Emit native reasoning through the public StreamingEvent.Thinking stream.
• Preserve incremental delivery without buffering complete reasoning blocks.
• Insert a newline between inference turns only when the preceding turn is unterminated.
• Keep the existing raw Flux<String> streaming contract compatible.
• Document native-thinking and inference-turn boundary behavior.

Testing

Added focused coverage for:

• Native-thinking metadata mapping in the Spring AI adapter.
• Original raw streaming compatibility.
• Native-thinking preservation before and after a tool call.
• Unterminated content separation across tool turns.
• Native thinking reaching the public structured-stream API.

Executed:

mvn -pl embabel-agent-api \
  -Dtest=StreamingToolLoopTest,SpringAiLlmMessageStreamerTest,StreamingLlmOperationsImplTest \
  test

Result:

Tests run: 14, Failures: 0, Errors: 0, Skipped: 0
BUILD SUCCESS

[igordayen]

@arnabnandy7 ... think was not triggered by native thinking. Perhaps put on hold for now.

for thinking streaming mode, works as expected:

abc....xyx bla bla bla NL ==> StreamEvent.Think ==xyx
abc... blabla .....NL ==> blabla .....

I may consider new interceptor in futurure to give developer both ==> getting stream with existing events AND aggregate, but this aggregation will be totally separately will not touch streaming logic.

Thanks.

[arnabnandy7]

@arnabnandy7 ... think was not triggered by native thinking. Perhaps put on hold for now.

for thinking streaming mode, works as expected:

abc....xyx bla bla bla NL ==> StreamEvent.Think ==xyx
abc... blabla .....NL ==> blabla .....

I may consider new interceptor in futurure to give developer both ==> getting stream with existing events AND aggregate, but this aggregation will be totally separately will not touch streaming logic.

Thanks.

Should I close the issue and PR/mark it as draft for now?

[igordayen]

Should I close the issue and PR/mark it as draft for now?

@arnabnandy7 please keep as a draft this week, and I appreciate patience and cooperation. will resume streaming track after release. thanks