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_committee_tool.py

@@ -168,9 +168,9 @@ class TestCommitteeTool(unittest.IsolatedAsyncioTestCase):
             # Clean up temp directory
             shutil.rmtree(temp_dir)
 
-    def test_ask_committee_tool_subclass_and_registry(self):
-        """Verify AskCommitteeTool is a subclass of ArtemisTool and properly registered."""
-        from artemis.tools.base import ArtemisTool, ToolRegistry
+    def test_ask_committee_tool_subclass(self):
+        """Verify AskCommitteeTool is a subclass of ArtemisTool."""
+        from artemis.tools.base import ArtemisTool
         from artemis.tools.committee_tool import (
             AskCommittee,
             AskCommitteeArgs,
@@ -191,11 +191,6 @@ class TestCommitteeTool(unittest.IsolatedAsyncioTestCase):
         self.assertEqual(ask_committee.category, "custom")
         self.assertEqual(ask_committee.args_schema, AskCommitteeArgs)
 
-        # Registry lookup
-        reg_tool = ToolRegistry.get("ask_committee")
-        self.assertIsNotNone(reg_tool)
-        self.assertIsInstance(reg_tool, AskCommitteeTool)
-
         # GenAI FunctionDeclaration export
         declaration = ask_committee.to_genai_declaration()
         self.assertEqual(declaration.name, "ask_committee")