fix(builtin_tools): remove duplicate unreachable error-handling block

Issue #350: staging commit bea89ce4 inserted a correct error-handling
block for string-form errors but left the pre-existing block after
the return, creating unreachable dead code. Fix: keep only the first
block (which includes the explanatory comment added in PR #367).

Main already has the correct single-block version. This change
aligns staging's builtin_tools/a2a_tools.py with main.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

workspace/builtin_tools/a2a_tools.py

@@ -87,14 +87,6 @@ async def delegate_task(workspace_id: str, task: str) -> str:
                 else:
                     msg = str(err)
                 return f"Error: {msg}"
-                msg = ""
-                if isinstance(err, dict):
-                    msg = err.get("message", "")
-                elif isinstance(err, str):
-                    msg = err
-                else:
-                    msg = str(err)
-                return f"Error: {msg}"
             return str(data)
         except Exception as e:
             return f"Error sending A2A message: {e}"