fix(agui): emit frontend tool args from fragment deltas

[dragondyt]

Related issues

• Fixes [Bug]: AG-UI frontend tools miss TOOL_CALL_ARGS when streamed name is __fragment__ #2873

Summary

• Record the real tool name on ToolCallStart and match frontend tools by toolCallId.
• Emit TOOL_CALL_ARGS for frontend tools even when streamed deltas use __fragment__.
• Keep backend tool args hidden when emitToolCallArgs is false.
• Add unit coverage for frontend and backend fragment deltas.

Breaking Changes

None.

[codecov]

Codecov Report

❌ Patch coverage is 92.00000% with 2 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
.../core/agui/adapter/strategy/AguiStreamContext.java	88.23%	0 Missing and 2 partials ⚠️

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[dragondyt]

CI失败与本次提交无关

[Aias00]

Matches #2873 exactly: the real tool name is captured on ToolCallStart and the frontend-tool decision is made from toolCallId instead of the __fragment__ placeholder, so frontend tools keep receiving TOOL_CALL_ARGS while backend tools stay hidden under emitToolCallArgs=false.

Deliberate details I checked and like:

• The raw (pre-normalisation) name is stored, so matching is against what the client actually declared in RunAgentInput.tools.
• Collectors.toSet() rather than toUnmodifiableSet() — the latter would NPE on a null AguiTool.name.
• isFrontendToolCall degrades to false when the start event was never seen, so the previous opt-in behaviour is preserved.

Tests cover both directions (frontend emits, backend does not) with the exact placeholder-name stream from the issue.

Note on CI: the build (windows-latest) failure is unrelated — it is SessionEventLogCrossProcessTest.subscribeAfterCursorSkipsEarlierEvents in service-common failing with a Reactor OverflowException from interval backpressure, a known Windows timing flake.

One non-blocking nit inline about pruning the new map. Approving.