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_log_tool.py

@@ -16,7 +16,7 @@ from unittest.mock import AsyncMock, MagicMock, patch
 
 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.log_tool import (
     AnalyzeLogs,
     AnalyzeLogsArgs,
@@ -88,8 +88,8 @@ async def test_analyze_logs_tool_no_context():
     assert result == "Error: ArtemisContext is required for LogAnalyzer."
 
 
-def test_analyze_logs_tool_subclass_and_registry():
-    """Verify AnalyzeLogsTool is an ArtemisTool subclass and registered in ToolRegistry."""
+def test_analyze_logs_tool_subclass():
+    """Verify AnalyzeLogsTool is an ArtemisTool subclass."""
     assert issubclass(AnalyzeLogsTool, ArtemisTool)
     assert issubclass(AnalyzeLogs, ArtemisTool)
     assert issubclass(LogTool, ArtemisTool)
@@ -100,11 +100,6 @@ def test_analyze_logs_tool_subclass_and_registry():
     assert analyze_logs.category == "custom"
     assert analyze_logs.args_schema == AnalyzeLogsArgs
 
-    # Registry lookup
-    reg_tool = ToolRegistry.get("analyze_logs")
-    assert reg_tool is not None
-    assert isinstance(reg_tool, AnalyzeLogsTool)
-
     # GenAI FunctionDeclaration export
     declaration = analyze_logs.to_genai_declaration()
     assert declaration.name == "analyze_logs"