A2A inbound message conversion ignores Message.role, always maps to "model"

[YizukiAme]

Bug Description

convert_a2a_message_to_event() in to_adk_event.py hard-codes role="model" for all resulting ADK events, regardless of the original A2A Message.role. User messages (Role.user) are incorrectly restored as model events.

The task history fallback (a2a_task.history[-1]) also does not check Message.role, so a trailing user message can be treated as agent output.

Steps to Reproduce

from a2a.types import Message, Part, TextPart, Role

user_msg = Message(
    role=Role.user,
    parts=[Part(root=TextPart(text="Hello"))],
    metadata={}
)
event = convert_a2a_message_to_event(user_msg, author="user")
# event author is always "model" — should reflect "user"

Expected Behavior

• A2A Role.user should map to an ADK event with role="user"
• History fallback should only use agent-role messages to avoid misattribution

Affected Files

• src/google/adk/a2a/converters/to_adk_event.py

[enjoykumawat]

I'd like to work on this. The fix should map Message.role to the correct ADK event author/role instead of hard-coding "model" in convert_a2a_message_to_event(). Will submit a PR shortly.

[anowardear062-svg]

Thanks

[surajksharma07]

@YizukiAme _create_event() in to_adk_event.py hardcodes role="model" and never reads a2a_message.role, which is what's causing the misattribution.

As a quick workaround, try wrapping convert_a2a_message_to_event() and fixing the role post-call via event.model_copy(update={"content": event.content.model_copy(update={"role": "user" if msg.role == Role.user else "model"})}).

It's also worth filtering history[-1] to agent-role only to avoid the second misattribution while you're in there.

Could you give that a try and let us know if it clears both issues on your end?
PR #5224 is already heading in this direction, so your confirmation there before it moves forward would be really helpful!

[YizukiAme]

Thanks @surajksharma07! I reviewed the diff in PR #5224 and the fix looks correct for both issues:

1. Role hardcoding: a2a_role_to_genai_role() correctly maps Role.user → "user" in both event_converter.py and to_adk_event.py.
2. History fallback: history[-1] is now filtered to Role.agent only, preventing trailing user messages from being misattributed.

(I originally found this via code audit rather than a live A2A setup, so my verification is code-level. But the root cause was a hardcoded string, and the fix + regression tests clearly address it.)

LGTM from the reporter side~ 👍

[surajksharma07]

Thanks for the thorough review @YizukiAme — a code-level LGTM is completely valid here given the root cause was a straightforward hardcode with no ambiguity.

We currently have two PRs open targeting the same fix (#5198 by @enjoykumawat and #5224 by @giulio-leone), so the team will review both and consolidate before merging.

We'll get this closed out once one lands — really appreciate you circling back so quickly!