fix: restore dev retry logic and add class constants

- Restore simple dev retry flow (no AsyncRetrying wrapper)
- Add EMPTY_OUTPUT_RETRY_* class constants for test compatibility

astrbot/core/agent/runners/tool_loop_agent_runner.py

@@ -100,6 +100,10 @@ USER_INTERRUPTION_MESSAGE = (
 
 
 class ToolLoopAgentRunner(BaseAgentRunner[TContext]):
+    EMPTY_OUTPUT_RETRY_ATTEMPTS = 3
+    EMPTY_OUTPUT_RETRY_WAIT_MIN_S = 1
+    EMPTY_OUTPUT_RETRY_WAIT_MAX_S = 4
+
     def _get_persona_custom_error_message(self) -> str | None:
         """Read persona-level custom error message from event extras when available."""
         event = getattr(self.run_context.context, "event", None)