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/explorer/universal_runner.py

@@ -15,10 +15,7 @@
 """Universal (LangChain ChatModel) execution loop for the Explorer agent.
 
 Split out of ``artemis.agents.explorer.explorer``: the ``_run_universal``
-reasoning loop, packaged as a mixin consumed by ``Explorer``.  Patched
-collaborators (``get_llm``, ``logger``, ``UNIVERSAL_EXPLORER_TOOLS``) are
-resolved through the facade module at call time; see
-``artemis.agents.explorer._facade``.
+reasoning loop, packaged as a mixin consumed by ``Explorer``.
 """
 
 import asyncio
@@ -33,10 +30,14 @@ from langchain_core.messages import (
     ToolMessage,
 )
 
-from artemis.agents.explorer._facade import facade
 from artemis.agents.explorer.geometry import is_valid_norm_point
 from artemis.agents.explorer.tiers import SUBMIT_TOOL
+from artemis.agents.explorer.tool_declarations import UNIVERSAL_EXPLORER_TOOLS
 from artemis.graph.state import State
+from artemis.services.llm import get_llm
+from artemis.utils.logger import get_logger
+
+logger = get_logger(__name__)
 
 
 class UniversalRunnerMixin:
@@ -72,9 +73,8 @@ class UniversalRunnerMixin:
 
     def _universal_exposed_tools(self) -> list[dict[str, Any]]:
         """OpenAI-style tool schemas the model may see (tier-hidden ones excluded)."""
-        _ex = facade()
         hidden = self._hidden_tool_names()
-        return [t for t in _ex.UNIVERSAL_EXPLORER_TOOLS if t["function"]["name"] not in hidden]
+        return [t for t in UNIVERSAL_EXPLORER_TOOLS if t["function"]["name"] not in hidden]
 
     async def _run_universal(
         self,
@@ -88,8 +88,7 @@ class UniversalRunnerMixin:
         max_turns: int,
     ) -> str:
         """Executes the Explorer reasoning loop via a universal LangChain ChatModel."""
-        _ex = facade()
-        llm = _ex.get_llm(self.ctx, name="explorer")
+        llm = get_llm(self.ctx, name="explorer")
 
         exposed_tools = self._universal_exposed_tools()
         bound_llm = llm.bind_tools(exposed_tools)
@@ -124,7 +123,7 @@ class UniversalRunnerMixin:
 
             tool_calls = getattr(response, "tool_calls", None) or []
             if not tool_calls:
-                _ex.logger.warning(f"Universal Explorer turn {turn}: No tool calls generated.")
+                logger.warning(f"Universal Explorer turn {turn}: No tool calls generated.")
                 if is_final_turn:
                     return json.dumps(
                         {
@@ -256,7 +255,6 @@ class UniversalRunnerMixin:
         the images ride on a follow-up human turn instead; unreadable files
         are skipped so a missing annotation never aborts the loop.
         """
-        _ex = facade()
         blocks: list[dict[str, Any]] = []
         tool_names: list[str] = []
         for tool_name, path in images:
@@ -264,7 +262,7 @@ class UniversalRunnerMixin:
                 with open(path, "rb") as f:
                     img_b64 = base64.b64encode(f.read()).decode("utf-8")
             except OSError as read_err:
-                _ex.logger.warning(f"Skipping unreadable tool image {path}: {read_err}")
+                logger.warning(f"Skipping unreadable tool image {path}: {read_err}")
                 continue
             if tool_name not in tool_names:
                 tool_names.append(tool_name)
@@ -283,7 +281,6 @@ class UniversalRunnerMixin:
         self, tool_calls: list, messages: list[BaseMessage], turn: int
     ) -> None:
         """Executes non-submit tool calls, appending ToolMessages and their images."""
-        _ex = facade()
         images: list[tuple[str, str]] = []
         for tc in tool_calls:
             name = tc.get("name")
@@ -306,7 +303,7 @@ class UniversalRunnerMixin:
                 messages.append(ToolMessage(tool_call_id=call_id, name=name, content=res_text))
                 images.extend((name, path) for path in self._tool_image_paths(res))
             except Exception as tool_err:
-                _ex.logger.error(f"Error executing tool '{name}': {tool_err}")
+                logger.error(f"Error executing tool '{name}': {tool_err}")
                 messages.append(
                     ToolMessage(
                         tool_call_id=call_id,