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.

tests/unit/tools/test_object_detection_tool.py

@@ -21,7 +21,7 @@ from langchain_core.messages import ToolMessage
 
 from artemis.context import ArtemisContext
 from artemis.graph.state import State
-from artemis.tools.base import ArtemisTool, ToolRegistry
+from artemis.tools.base import ArtemisTool
 from artemis.tools.object_detection_tool import (
     ObjectDetection,
     ObjectDetectionArgs,
@@ -41,7 +41,7 @@ from artemis.tools.object_detection_tool import (
 import pytest
 
 
-def test_object_detection_tool_subclass_and_registry():
+def test_object_detection_tool_subclass():
     """Verify ObjectDetectionTool and OperatorObjectDetectionTool subclass ArtemisTool and register."""
     assert issubclass(ObjectDetectionTool, ArtemisTool)
     assert issubclass(ObjectDetection, ArtemisTool)
@@ -65,11 +65,6 @@ def test_object_detection_tool_subclass_and_registry():
     assert operator_object_detection.category == "perception"
     assert operator_object_detection.args_schema == OperatorObjectDetectionArgs
 
-    # Registry lookup
-    reg_tool = ToolRegistry.get("object_detection")
-    assert reg_tool is not None
-    assert isinstance(reg_tool, ObjectDetectionTool)
-
     # GenAI FunctionDeclaration export
     declaration = object_detection.to_genai_declaration()
     assert declaration.name == "object_detection"