refactor(agent): make resolver sole runtime owner

tests/agent/test_self_model_preset.py

@@ -54,9 +54,10 @@ def test_model_preset_setter_updates_state(tmp_path) -> None:
     assert loop.model_preset == "fast"
     assert loop.model == "openai/gpt-4.1"
     assert loop.context_window_tokens == 32_768
-    assert loop.provider.generation.temperature == 0.5
-    assert loop.provider.generation.max_tokens == 4096
-    assert loop.provider.generation.reasoning_effort == "low"
+    runtime = loop.llm_runtime()
+    assert runtime.generation.temperature == 0.5
+    assert runtime.generation.max_tokens == 4096
+    assert runtime.generation.reasoning_effort == "low"
     assert not hasattr(loop.subagents, "model")
     assert not hasattr(loop.consolidator, "model")
     assert not hasattr(loop.consolidator, "context_window_tokens")
@@ -174,7 +175,7 @@ def test_active_model_preset_survives_unchanged_config_refresh(tmp_path) -> None
     )
 
     loop.set_model_preset("fast")
-    loop._refresh_provider_snapshot()
+    loop.llm_runtime()
 
     assert loop.model_preset == "fast"
     assert loop.provider is fast_provider
@@ -210,7 +211,7 @@ def test_config_model_refresh_clears_active_model_preset(tmp_path) -> None:
     )
 
     loop.set_model_preset("fast")
-    loop._refresh_provider_snapshot()
+    loop.llm_runtime()
 
     assert loop.model_preset is None
     assert loop.provider is webui_provider
@@ -292,7 +293,7 @@ def test_self_tool_set_model_clears_active_preset(tmp_path) -> None:
     tool = MyTool(runtime_state=loop, modify_allowed=True)
     result = tool._modify("model", "anthropic/claude-opus-4-5")
     assert "Error" not in result
-    assert loop._active_preset is None
+    assert loop.model_preset is None
     assert loop.model == "anthropic/claude-opus-4-5"
 
 
@@ -323,5 +324,7 @@ def test_from_config_static_preset_loader_does_not_enable_hot_reload(tmp_path) -
     fake_provider = _provider("openai/gpt-4.1")
     with patch("nanobot.providers.factory.make_provider", return_value=fake_provider):
         loop = AgentLoop.from_config(config)
-    assert loop._provider_snapshot_loader is None
-    assert loop._preset_snapshot_loader is not None
+        default_runtime = loop.runtime_resolver.runtime
+        resolved = loop.runtime_resolver.resolve_preset("fast")
+    assert resolved.model == "openai/gpt-4.1-mini"
+    assert loop.runtime_resolver.runtime is default_runtime