fix(ag-ui):subagent event forward

[rudy2steiner]

Background

Fixes #1046 When a supervisor agent delegates to a sub-agent via SubAgentTool with SubAgentConfig.forwardEvents(true), the sub-agent's intermediate
reasoning/text was completely invisible to the AG-UI frontend — the UI saw TOOL_CALL_START, then a long pause, then TOOL_CALL_END + TOOL_CALL_RESULT arriving together. Effectively a "black box" during sub-agent execution,
especially painful for multi-step researchers/analysts.

Changes

• added a new branch for non-last TOOL_RESULT events for subagent events
• new unit test that constructs the same wire format SubAgentTool.forwardEvent produces, runs it through the adapter

[CLAassistant]

All committers have signed the CLA.

[codecov]

Codecov Report

❌ Patch coverage is 33.33333% with 10 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...io/agentscope/core/tool/subagent/SubAgentTool.java	0.00%	6 Missing ⚠️
...agentscope/core/agui/adapter/AguiAgentAdapter.java	55.55%	0 Missing and 4 partials ⚠️

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[AgentScopeJavaBot]

🤖 AI Review

This PR fixes the AG-UI adapter to correctly forward sub-agent intermediate events (reasoning/text) to the frontend when SubAgentTool has forwardEvents=true. The fix adds a new branch for non-last TOOL_RESULT events, extracting the inner Event from metadata and recursively converting it. Key concerns: (1) subagent_event magic string is a cross-module contract with no shared constant; (2) recursive convertEvent shares EventConversionState, risking currentTextMessageId state pollution; (3) no null-check on the inner Event extracted from metadata.

[AgentScopeJavaBot]

[major] subagent_event is a cross-module magic string shared between SubAgentTool (core) and this adapter (extensions). A typo here silently drops all sub-agent events. Extract to a shared constant, e.g. SubAgentTool.METADATA_KEY_SUBAGENT_EVENT, and add a debug log when the metadata value is not an Event instance.

[AgentScopeJavaBot]

[major] Recursive convertEvent(innerEvent, state) shares the same EventConversionState. If the sub-agent stream terminates without a final isLast=true REASONING event (e.g. cancellation, error), currentTextMessageId remains stuck on the sub-agent message ID, potentially corrupting subsequent supervisor text messages. Consider saving/restoring currentTextMessageId around the recursive call.

[rudy2steiner]

Won't fix. finishRun() already emits trailing TextMessageEnd for any unended message

[AgentScopeJavaBot]

[minor] No null/instance check on the value extracted from metadata. If the metadata contains a non-Event object, the recursive convertEvent call will fail with a ClassCastException. Add a defensive instanceof check before the recursive call.

[rudy2steiner]

Won't fix. inner instanceof Event innerEvent already does both null- and type-checking via pattern matching.won't fix

[itxaiohanglover]

Good refactor! Extracting metadata keys as public constants makes them usable by downstream consumers without string duplication. The AG-UI adapter integration looks clean — forwarding sub-agent events through the metadata channel is a pragmatic approach.