fix(core): apply transformed model-call text deltas

[zouyx]

AgentScope-Java Version

2.0.1-SNAPSHOT

Description

Fixes #2385.

MiddlewareBase.onModelCall can transform emitted TextBlockDeltaEvents, but those changes previously affected only the external event stream. The final Msg was still built from unmodified model chunks, causing native structured-output parsing to consume stale text.

This change rebuilds accumulated response text from the transformed model-call event stream before producing the final message. As a result, middleware can normalize text—such as removing Markdown JSON fences—before native structured-output parsing.

Added regression coverage for a model that streams fenced JSON across multiple chunks. The middleware removes the fence deltas, and the test verifies the final response contains valid JSON and deserializes into structured data.

Validation:

• mvn -pl agentscope-core -Dtest=ReActAgentStructuredOutputWithToolsTest,ReActAgentMiddlewareIntegrationTest test
• 12 tests passed.

Checklist

• Code has been formatted with mvn spotless:apply
• All tests are passing (mvn test)
• Javadoc comments are complete and follow project conventions
• Related documentation has been updated
• Code is ready for review

[gemini-code-assist]

Caution

The consumer version of Gemini Code Assist on GitHub has been sunset. All code review activity has officially ceased.

[oss-maintainer]

Review: fix(core): apply transformed model-call text deltas

Verdict: Approved ✅

Summary

Fixes #2385 — middleware onModelCall text delta transformations (e.g. removing Markdown JSON fences) were only reflected in the external event stream, not in the final Msg used for structured-output parsing. This PR rebuilds accumulated response text from the post-middleware event stream before producing the final message.

Code Quality

• Well-targeted fix — minimal change (+123/-1) touching exactly the right layers: ReActAgent, ReasoningContext, TextAccumulator, and MiddlewareBase Javadoc.
• Correct approach — doOnNext collects transformed text deltas, doOnComplete replaces accumulated text only when middleware actually produced deltas (sawTransformedTextDelta guard).
• Good test coverage — MarkdownFenceRemovingMiddleware test simulates a model streaming fenced JSON across 3 chunks, verifies the fence removal propagates to structured output parsing. 12 tests pass.
• Thread safety note — StringBuilder in doOnNext closure is safe here because model call streams are single-subscriber sequential SSE streams, consistent with existing TextAccumulator patterns.

Observations

• CLA not yet signed — contributor needs to sign before merge.
• CI builds still pending — will confirm once green.

[Copilot]

Pull request overview

This PR fixes a mismatch between middleware-transformed TextBlockDeltaEvent streams and the final accumulated response text used to construct the terminal Msg (notably impacting native structured-output parsing).

Changes:

• Rebuild accumulated response text from the (potentially middleware-transformed) TextBlockDeltaEvent stream before producing the final message.
• Document the middleware contract that TextBlockDeltaEvent transformations are reflected in the final response message.
• Add a regression test covering streamed fenced JSON where middleware removes Markdown fence deltas and structured output still deserializes correctly.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
agentscope-core/src/main/java/io/agentscope/core/ReActAgent.java	Accumulates transformed text deltas during onModelCall and replaces the reasoning context’s accumulated text at stream end.
agentscope-core/src/main/java/io/agentscope/core/middleware/MiddlewareBase.java	Updates onModelCall Javadoc to state that TextBlockDeltaEvent transformations are reflected in the final response.
agentscope-core/src/main/java/io/agentscope/core/agent/accumulator/TextAccumulator.java	Adds replace(String) to allow overwriting accumulated text from reconstructed transformed deltas.
agentscope-core/src/main/java/io/agentscope/core/agent/accumulator/ReasoningContext.java	Exposes replaceAccumulatedText(String) to swap accumulated text post-middleware transformation.
agentscope-core/src/test/java/io/agentscope/core/agent/ReActAgentStructuredOutputWithToolsTest.java	Adds a regression test ensuring middleware delta replacement updates native structured output parsing results.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!

[oss-maintainer]

LGTM. Clean, well-scoped fix for #2385.

Summary: Rebuilds accumulated response text from the post-middleware TextBlockDeltaEvent stream, so onModelCall transformations (e.g. stripping Markdown fences) are reflected in the final Msg used by native structured-output parsing.

Key observations:

• doOnNext/doOnComplete pattern is idiomatic Reactor — no shared mutable state, StringBuilder and AtomicBoolean are local per invocation.
• TextAccumulator.replace() has proper null safety.
• MiddlewareBase Javadoc update correctly documents the new contract.
• Regression test (fencedNativeResponder) is realistic: multi-chunk fenced JSON → middleware strips fences → final Msg contains valid JSON that deserializes.
• CI all green (build + codecov + CLA).

No concerns.