Python: [BREAKING] Fix #3613 chat/agent message typing alignment (#3920)

* Fix #3613 message typing across chat and agents

* Address #3613 review feedback and sample input style

* refactor: use shared AgentRunMessages aliases (#3613)

* refactor: rename agent run input aliases for #3613

* samples: inline image content in run calls

* core: export AgentRunInputs from package init

* core: use explicit init re-exports without __all__

* updated logging and inits

* Fix core mypy export and samples XML note

* Remove AgentRunInputsOrNone and dedupe loggers

* Remove prepare_messages helper

* fix integration tests

python/packages/a2a/agent_framework_a2a/_agent.py

@@ -40,6 +40,7 @@ from agent_framework import (
     normalize_messages,
     prepend_agent_framework_to_user_agent,
 )
+from agent_framework._types import AgentRunInputs
 from agent_framework.observability import AgentTelemetryLayer
 
 __all__ = ["A2AAgent", "A2AContinuationToken"]
@@ -208,7 +209,7 @@ class A2AAgent(AgentTelemetryLayer, BaseAgent):
     @overload
     def run(
         self,
-        messages: str | Message | Sequence[str | Message] | None = None,
+        messages: AgentRunInputs | None = None,
         *,
         stream: Literal[False] = ...,
         session: AgentSession | None = None,
@@ -220,7 +221,7 @@ class A2AAgent(AgentTelemetryLayer, BaseAgent):
     @overload
     def run(
         self,
-        messages: str | Message | Sequence[str | Message] | None = None,
+        messages: AgentRunInputs | None = None,
         *,
         stream: Literal[True],
         session: AgentSession | None = None,
@@ -231,7 +232,7 @@ class A2AAgent(AgentTelemetryLayer, BaseAgent):
 
     def run(
         self,
-        messages: str | Message | Sequence[str | Message] | None = None,
+        messages: AgentRunInputs | None = None,
         *,
         stream: bool = False,
         session: AgentSession | None = None,