[BUG] A2AClientToolProvider errors not surfaced as tool errors through @tool decorator #606

Checks

• I have updated to the lastest minor and patch version of Strands
• I have checked the documentation and this is not expected behavior
• I have searched ./issues and there are no duplicates of my issue

Strands Version

1.55.0

Tools Package Version

0.8.7

Tools used

a2a_send_message

Python Version

3.11

Operating System

AL2_x86_64

Installation Method

other

Steps to Reproduce

1. Create an A2AClientToolProvider with an unreachable agent URL
2. Register an AfterToolCallEvent hook that checks for status="error"
3. Call a2a_send_message through a Strands agent
4. The hook never fires - the ToolResult has status="success" with the error buried in text content

Expected Behavior

Expected behavior: a2a_send_message errors should produce status="error" tool results so downstream hooks and middleware can detect and respond to failures.

Actual Behavior

The result gets wrapped as status="success" with the error dict JSON-serialized as text content.

Additional Context

No response

Possible Solution

Add "content": [{"text": "..."}] to error return shapes while preserving existing keys for backward compatibility.

Related Issues

No response