fix: correct task scheduling and simplify agent internals

Fix queue cancellation, concurrency limits and worker status updates.

Use direct Explorer imports, split the Diagnoser loop into helpers and remove unused tool registration and prompt-builder code.

Correct model caching, endpoint selection and retry handling.

artemis/tools/diagnoser_submit_answer_tool.py

@@ -22,7 +22,7 @@ from pydantic import BaseModel, Field
 from artemis.context import ArtemisContext
 from artemis.data_engine.trace import trace_langchain_tool
 from artemis.drivers.base import BaseDeviceDriver
-from artemis.tools.base import ArtemisTool, ToolRegistry
+from artemis.tools.base import ArtemisTool
 from artemis.utils.logger import get_logger
 
 logger = get_logger(__name__)
@@ -80,7 +80,6 @@ class SubmitAnswerTool(ArtemisTool):
 submit_answer = SubmitAnswerTool()
 SubmitAnswer = SubmitAnswerTool
 DiagnoserSubmitAnswerTool = SubmitAnswerTool
-ToolRegistry.register(submit_answer)
 
 
 def get_submit_answer_tool(ctx: ArtemisContext) -> BaseTool: