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/mcp/test_action_specs.py

@@ -208,20 +208,14 @@ def test_operator_verbs_lower_onto_manifest_actions():
     )
 
 
-def test_registry_wait_for_delay_seconds_drift_stays_dead():
-    """Guards against re-growing a shadow device-action registration.
+def test_manifest_wait_for_delay_uses_milliseconds():
+    """The manifest's ``wait_for_delay`` takes ``time_in_ms``, never *seconds*.
 
     ``artemis/tools/actions/device_actions.py`` used to shadow-register a second
-    ``wait_for_delay`` taking *seconds* while every prompt teaches milliseconds
-    (the last such surface, ``artemis/tools/mobile/exec_tools.py``, is deleted).
-    The ToolRegistry must never again carry a ``wait_for_delay`` whose unit
-    disagrees with the manifest's ``time_in_ms``.
+    ``wait_for_delay`` taking *seconds* while every prompt teaches milliseconds.
+    The shadow ToolRegistry channel is deleted; the manifest is the only surface
+    left, and its unit must stay milliseconds.
     """
-    from artemis.tools.base import ToolRegistry
-
-    tool = ToolRegistry.get("wait_for_delay")
-    if tool is None:
-        return  # Not registered at all: nothing to drift.
-    fields = set(tool.args_schema.model_json_schema().get("properties", {}))
+    fields = set(tool_declaration("wait_for_delay").parameters["properties"])
     assert "seconds" not in fields
     assert "time_in_ms" in fields