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_wait_tool.py

@@ -17,7 +17,7 @@ import time
 from unittest.mock import AsyncMock, MagicMock
 
 from artemis.context import ArtemisContext
-from artemis.tools.base import ArtemisTool, ToolRegistry
+from artemis.tools.base import ArtemisTool
 from artemis.tools.wait_tool import (
     Wait,
     WaitArgs,
@@ -35,8 +35,8 @@ def mock_ctx():
     return ctx
 
 
-def test_wait_tool_subclass_and_registry():
-    """Verify WaitTool is a subclass of ArtemisTool and properly registered."""
+def test_wait_tool_subclass():
+    """Verify WaitTool is a subclass of ArtemisTool."""
     assert issubclass(WaitTool, ArtemisTool)
     assert issubclass(Wait, ArtemisTool)
     assert isinstance(wait, ArtemisTool)
@@ -46,11 +46,6 @@ def test_wait_tool_subclass_and_registry():
     assert wait.category == "system"
     assert wait.args_schema == WaitArgs
 
-    # Registry lookup
-    reg_tool = ToolRegistry.get("wait")
-    assert reg_tool is not None
-    assert isinstance(reg_tool, WaitTool)
-
     # GenAI FunctionDeclaration export
     declaration = wait.to_genai_declaration()
     assert declaration.name == "wait"