fix(harness): mark _RecordingTracer.handle with @OverRide (reportImplicitOverride)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: declan-scale

tests/lib/core/harness/conformance/runner.py

@@ -49,7 +49,7 @@
 from __future__ import annotations
 
 import types as _types
-from typing import Any, NamedTuple
+from typing import Any, NamedTuple, override
 from dataclasses import dataclass
 
 from agentex.types.task_message import TaskMessage
@@ -267,6 +267,7 @@ def __init__(self, tracing: Any) -> None:
         )
         self.received_signals: list[SpanSignal] = []
 
+    @override
     async def handle(self, signal: SpanSignal) -> None:
         self.received_signals.append(signal)
         await super().handle(signal)