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/agents/operator/operator.py

@@ -82,7 +82,7 @@ from artemis.agents.operator.prompts import (
     InjectedInstructionPromptComponent,
     render_transcript_static_system,
 )
-from artemis.agents.operator.prompt_builder import load_operator_prompts
+from artemis.agents.operator.prompts import load_operator_prompts
 
 
 class OperatorNode:
@@ -101,8 +101,7 @@ class OperatorNode:
         try:
             self.prompts = load_operator_prompts()
         except (OSError, ValueError, json.JSONDecodeError) as e:
-            logger.error(f"Failed to load operator prompts: {e}")
-            self.prompts = {}
+            raise RuntimeError(f"Failed to load operator prompts: {e}") from e
 
         # M2 transcript flag (agent.memory.transcript.enabled). Off keeps the
         # legacy 2-message prompt path byte-for-byte; an explicit
@@ -488,8 +487,7 @@ class OperatorNode:
             additional_kwargs = getattr(response, "additional_kwargs", None)
             if (
                 not response.tool_calls
-                and isinstance(additional_kwargs, dict)
-                and not hasattr(additional_kwargs, "assert_called_with")  # Filter out mocks
+                and type(additional_kwargs) is dict
                 and additional_kwargs.get("function_call")
             ):
                 fc = additional_kwargs["function_call"]