feat(agui): Add multimodal input support (image/video/audio) to AguiM…

[NoiAI]

…essage and AguiMessageConverter

Adds support for multimodal input (image, video, audio, document) in the AG-UI extension, aligning with the AG-UI Protocol InputContent specification.

• AguiMessage.content: String -> Object (backward compatible)
• AguiMessageConverter: InputContent[] -> ContentBlock conversion
• Supports both url and data (base64) source types

AgentScope-Java Version

[The version of AgentScope-Java you are working on, e.g. 1.0.12, check your pom.xml dependency version or run mvn dependency:tree | grep agentscope-parent:pom(only mac/linux)]

Description

[Please describe the background, purpose, changes made, and how to test this PR]

Checklist

Please check the following items before code is ready to be reviewed.

• 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 (e.g. links, examples, etc.)
• Code is ready for review

[CLAassistant]

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[codecov]

Codecov Report

❌ Patch coverage is 84.61538% with 8 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...cope/core/agui/converter/AguiMessageConverter.java	83.67%	3 Missing and 5 partials ⚠️

📢 Thoughts on this report? Let us know!

[zhengxudong]

这个功能对我们项目非常重要，我们已经测试过可以正常使用，希望能尽快合并，非常感谢！

[LearningGp]

PTAL @chickenlj

[junnan2014]

We have a real-world need for this feature (Spring Boot + HarnessAgent + DashScope + AG-UI web client, where users send images/audio recordings from the browser). Currently we have to work around the protocol layer by smuggling attachments through forwardedProps and rebuilding Msg content blocks in an Agent decorator — this PR would remove that workaround entirely.

To help move this forward, I independently verified this PR today (2026-07-28):

• ✅ On the PR branch as-is: mvn test on the agui module passes — 231 tests, 0 failures (including the 81 new multimodal test cases).
• • ✅ Cherry-picked 5d6cb4b onto latest main (ed81704): applies with zero conflicts — git rename detection handles the module move to agentscope-extensions-protocol/ transparently.
• • ✅ Latest main + this patch: agui module passes 258 tests, 0 failures.
    The approach also aligns well with the AG-UI protocol InputContent spec (https://docs.ag-ui.com/drafts/multimodal-messages), and the downstream conversion path is already in place (ImageBlock/AudioBlock/VideoBlock in core, DashScopeMediaConverter etc. in model extensions) — this protocol-layer gap is the only missing piece for end-to-end multimodal via AG-UI.

@chickenlj @LearningGp Could this get a review? If the original author is no longer available, I'd be happy to help rebase, fill in the PR description checklist, and cover the remaining uncovered lines flagged by codecov.

[oss-maintainer]

3. @SuppressWarnings("unchecked") — Multiple unchecked casts from Map<String, Object>. This is acceptable given JSON deserialization constraints, but consider adding a typed DTO (e.g., InputContent) for type safety in a follow-up.

4. CLA not signed — The CLA assistant flag is still pending. Please sign the CLA at https://cla-assistant.io/agentscope-ai/agentscope-java?pullRequest=1380 before this can be merged.

5. May need rebase — This PR has been open since May. Please rebase onto current main to ensure no merge conflicts with recent AG-UI changes (e.g., PR #2452 metadata field, PR #2463 toolkit refactoring).

Verdict

Solid implementation of a much-requested feature. The core conversion logic is correct and well-tested. Addressing the document data loss (#1) and rebasing would make this merge-ready.