fix(config): reconcile presets with settings reload

Co-authored-by: Cursor <cursoragent@cursor.com>

nanobot/agent/loop.py

@@ -293,7 +293,7 @@ class AgentLoop:
         provider_signature: tuple[object, ...] | None = None,
         model_presets: dict[str, ModelPresetConfig] | None = None,
         model_preset: str | None = None,
-        model_preset_snapshot_builder: Callable[[ModelPresetConfig], ProviderSnapshot] | None = None,
+        model_preset_snapshot_builder: Callable[[str], ProviderSnapshot] | None = None,
     ):
         from nanobot.config.schema import ToolsConfig
 
@@ -304,6 +304,10 @@ class AgentLoop:
         self.provider = provider
         self._provider_snapshot_loader = provider_snapshot_loader
         self._provider_signature = provider_signature
+        self._config_provider_signature = provider_signature
+        self._config_default_selection_signature = (
+            provider_signature[:2] if provider_signature is not None else None
+        )
         self.workspace = workspace
         self.model = model or provider.get_default_model()
         self.max_iterations = (
@@ -431,6 +435,7 @@ class AgentLoop:
         resolved = config.resolve_preset()
         model = extra.pop("model", None) or resolved.model
         context_window_tokens = extra.pop("context_window_tokens", None) or resolved.context_window_tokens
+        model_preset_snapshot_builder = extra.pop("model_preset_snapshot_builder", None)
         model_presets = dict(config.model_presets)
         if "default" not in model_presets:
             model_presets["default"] = resolved
@@ -457,7 +462,10 @@ class AgentLoop:
             tools_config=config.tools,
             model_presets=model_presets,
             model_preset=defaults.model_preset,
-            model_preset_snapshot_builder=lambda preset: build_provider_snapshot(config, preset=preset),
+            model_preset_snapshot_builder=(
+                model_preset_snapshot_builder
+                or (lambda name: build_provider_snapshot(config, preset_name=name))
+            ),
             **extra,
         )
 
@@ -489,8 +497,32 @@ class AgentLoop:
         except Exception:
             logger.exception("Failed to refresh provider config")
             return
+        if self._active_preset:
+            default_selection = snapshot.signature[:2]
+            if (
+                self._config_default_selection_signature is not None
+                and default_selection != self._config_default_selection_signature
+            ):
+                self._active_preset = None
+                self._config_provider_signature = snapshot.signature
+                self._config_default_selection_signature = default_selection
+                self._apply_provider_snapshot(snapshot)
+                return
+            self._config_provider_signature = snapshot.signature
+            self._config_default_selection_signature = default_selection
+            try:
+                snapshot = self._build_model_preset_snapshot(self._active_preset)
+            except Exception:
+                logger.exception("Failed to refresh active model preset")
+                return
+            if snapshot.signature == self._provider_signature:
+                return
+            self._apply_provider_snapshot(snapshot)
+            return
         if snapshot.signature == self._provider_signature:
             return
+        self._config_provider_signature = snapshot.signature
+        self._config_default_selection_signature = snapshot.signature[:2]
         self._apply_provider_snapshot(snapshot)
 
     # -- model_preset property --
@@ -506,7 +538,7 @@ class AgentLoop:
     def _build_model_preset_snapshot(self, name: str) -> ProviderSnapshot:
         preset = self.model_presets[name]
         if self._model_preset_snapshot_builder is not None:
-            return self._model_preset_snapshot_builder(preset)
+            return self._model_preset_snapshot_builder(name)
         self.provider.generation = preset.to_generation_settings()
         return ProviderSnapshot(
             provider=self.provider,

nanobot/cli/commands.py

@@ -672,6 +672,7 @@ def _run_gateway(
             "aihubmix": config.providers.aihubmix,
         },
         provider_snapshot_loader=load_provider_snapshot,
+        model_preset_snapshot_builder=lambda name: load_provider_snapshot(preset_name=name),
         provider_signature=provider_snapshot.signature,
     )
 

nanobot/providers/factory.py

@@ -143,7 +143,14 @@ def build_provider_snapshot(
     )
 
 
-def load_provider_snapshot(config_path: Path | None = None) -> ProviderSnapshot:
+def load_provider_snapshot(
+    config_path: Path | None = None,
+    *,
+    preset_name: str | None = None,
+) -> ProviderSnapshot:
     from nanobot.config.loader import load_config, resolve_config_env_vars
 
-    return build_provider_snapshot(resolve_config_env_vars(load_config(config_path)))
+    return build_provider_snapshot(
+        resolve_config_env_vars(load_config(config_path)),
+        preset_name=preset_name,
+    )

tests/agent/test_self_model_preset.py

@@ -80,11 +80,11 @@ def test_model_preset_setter_replaces_provider_from_snapshot(tmp_path) -> None:
         model="base-model",
         context_window_tokens=1000,
         model_presets={"deep": preset},
-        model_preset_snapshot_builder=lambda _preset: ProviderSnapshot(
+        model_preset_snapshot_builder=lambda _name: ProviderSnapshot(
             provider=new_provider,
-            model=_preset.model,
+            model=preset.model,
-            context_window_tokens=_preset.context_window_tokens,
+            context_window_tokens=preset.context_window_tokens,
-            signature=("deep", _preset.model),
+            signature=("deep", preset.model),
         ),
     )
 
@@ -111,7 +111,7 @@ def test_model_preset_setter_failure_leaves_old_state(tmp_path) -> None:
         model="base-model",
         context_window_tokens=1000,
         model_presets={"fast": preset},
-        model_preset_snapshot_builder=lambda _preset: (_ for _ in ()).throw(
+        model_preset_snapshot_builder=lambda _name: (_ for _ in ()).throw(
             RuntimeError("provider unavailable")
         ),
     )
@@ -128,6 +128,78 @@ def test_model_preset_setter_failure_leaves_old_state(tmp_path) -> None:
     assert loop.consolidator.max_completion_tokens == 123
 
 
+def test_active_model_preset_survives_unchanged_config_refresh(tmp_path) -> None:
+    base_provider = _provider("base-model", max_tokens=123)
+    fast_provider = _provider("openai/gpt-4.1", max_tokens=4096)
+    default_snapshot = ProviderSnapshot(
+        provider=base_provider,
+        model="base-model",
+        context_window_tokens=1000,
+        signature=("base-model", "auto", "openai", "sk-old"),
+    )
+    fast_snapshot = ProviderSnapshot(
+        provider=fast_provider,
+        model="openai/gpt-4.1",
+        context_window_tokens=32_768,
+        signature=("openai/gpt-4.1", "auto", "openai", "sk-old"),
+    )
+    loop = AgentLoop(
+        bus=MessageBus(),
+        provider=base_provider,
+        workspace=tmp_path,
+        model="base-model",
+        context_window_tokens=1000,
+        provider_snapshot_loader=lambda: default_snapshot,
+        provider_signature=default_snapshot.signature,
+        model_presets={"fast": ModelPresetConfig(model="openai/gpt-4.1")},
+        model_preset_snapshot_builder=lambda _name: fast_snapshot,
+    )
+
+    loop.set_model_preset("fast")
+    loop._refresh_provider_snapshot()
+
+    assert loop.model_preset == "fast"
+    assert loop.provider is fast_provider
+    assert loop.model == "openai/gpt-4.1"
+
+
+def test_config_model_refresh_clears_active_model_preset(tmp_path) -> None:
+    base_provider = _provider("base-model", max_tokens=123)
+    fast_provider = _provider("openai/gpt-4.1", max_tokens=4096)
+    webui_provider = _provider("anthropic/claude-opus-4-5", max_tokens=2048)
+    webui_snapshot = ProviderSnapshot(
+        provider=webui_provider,
+        model="anthropic/claude-opus-4-5",
+        context_window_tokens=200_000,
+        signature=("anthropic/claude-opus-4-5", "anthropic", "anthropic", "sk-old"),
+    )
+    fast_snapshot = ProviderSnapshot(
+        provider=fast_provider,
+        model="openai/gpt-4.1",
+        context_window_tokens=32_768,
+        signature=("openai/gpt-4.1", "auto", "openai", "sk-old"),
+    )
+    loop = AgentLoop(
+        bus=MessageBus(),
+        provider=base_provider,
+        workspace=tmp_path,
+        model="base-model",
+        context_window_tokens=1000,
+        provider_snapshot_loader=lambda: webui_snapshot,
+        provider_signature=("base-model", "auto", "openai", "sk-old"),
+        model_presets={"fast": ModelPresetConfig(model="openai/gpt-4.1")},
+        model_preset_snapshot_builder=lambda _name: fast_snapshot,
+    )
+
+    loop.set_model_preset("fast")
+    loop._refresh_provider_snapshot()
+
+    assert loop.model_preset is None
+    assert loop.provider is webui_provider
+    assert loop.model == "anthropic/claude-opus-4-5"
+    assert loop.context_window_tokens == 200_000
+
+
 def test_model_preset_setter_raises_on_unknown(tmp_path) -> None:
     loop = _make_loop(tmp_path)
     with pytest.raises(KeyError, match="model_preset 'missing' not found"):