Is your feature request related to a problem? Please describe.

Citations are essential for showing used sources when doing RAG, web search, or other external knowledge sources. Including citations is now quite common in agents, and some LLM providers even support them directly (like Claude and Cohere). It's clear that the concept of citations will be common for many agents, and thus would benefit from a centralized spec for better interoperability between A2A agents, and centralized support in A2A-compatible UIs.

Since the concept of citations is quite simple (just a text range and a source URL, in its most basic form), and the benefits of standardizing are possibly quite high, we propose adding the concept of citations to A2A.

Describe the solution you'd like

The exact form is up to discussion. It may be a direct implementation in the core A2A protocol, an official protocol extension, or endorsing a 3rd party extension.

The BeeAI project already includes a citation extension in the beeai-sdk (https://github.com/i-am-bee/beeai-platform/blob/main/apps/beeai-sdk/src/beeai_sdk/a2a/extensions/ui/citation.py), used by the bundled BeeAI agents as well as some internal IBM agents, end-to-end tested and UI-compatible. This extension could be possibly "graduated" to an official, or officially endorsed, A2A extension.

Describe alternatives you've considered

No response

Additional context

No response

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