fix(config): make model preset switching atomic

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

tests/command/test_model_command.py

@@ -0,0 +1,137 @@
+from types import SimpleNamespace
+from unittest.mock import MagicMock
+
+import pytest
+
+from nanobot.agent.loop import AgentLoop
+from nanobot.bus.events import InboundMessage
+from nanobot.bus.queue import MessageBus
+from nanobot.command.builtin import (
+    build_help_text,
+    builtin_command_palette,
+    cmd_model,
+    register_builtin_commands,
+)
+from nanobot.command.router import CommandContext, CommandRouter
+from nanobot.config.schema import ModelPresetConfig
+
+
+def _provider(default_model: str, max_tokens: int = 123) -> MagicMock:
+    provider = MagicMock()
+    provider.get_default_model.return_value = default_model
+    provider.generation = SimpleNamespace(
+        max_tokens=max_tokens,
+        temperature=0.1,
+        reasoning_effort=None,
+    )
+    return provider
+
+
+def _make_loop(tmp_path) -> AgentLoop:
+    return AgentLoop(
+        bus=MessageBus(),
+        provider=_provider("base-model", max_tokens=123),
+        workspace=tmp_path,
+        model="base-model",
+        context_window_tokens=1000,
+        model_presets={
+            "default": ModelPresetConfig(
+                model="base-model",
+                max_tokens=123,
+                context_window_tokens=1000,
+            ),
+            "fast": ModelPresetConfig(
+                model="openai/gpt-4.1",
+                max_tokens=4096,
+                context_window_tokens=32_768,
+            ),
+        },
+    )
+
+
+def _ctx(loop: AgentLoop, raw: str, args: str = "") -> CommandContext:
+    msg = InboundMessage(channel="cli", sender_id="user", chat_id="direct", content=raw)
+    return CommandContext(msg=msg, session=None, key=msg.session_key, raw=raw, args=args, loop=loop)
+
+
+@pytest.mark.asyncio
+async def test_model_command_lists_current_and_available_presets(tmp_path) -> None:
+    loop = _make_loop(tmp_path)
+
+    out = await cmd_model(_ctx(loop, "/model"))
+
+    assert "Current model: `base-model`" in out.content
+    assert "Active preset: `(none)`" in out.content
+    assert "`default`" in out.content
+    assert "`fast`" in out.content
+    assert out.metadata == {"render_as": "text"}
+
+
+@pytest.mark.asyncio
+async def test_model_command_switches_preset(tmp_path) -> None:
+    loop = _make_loop(tmp_path)
+
+    out = await cmd_model(_ctx(loop, "/model fast", args="fast"))
+
+    assert "Switched model preset to `fast`." in out.content
+    assert "Model: `openai/gpt-4.1`" in out.content
+    assert loop.model_preset == "fast"
+    assert loop.model == "openai/gpt-4.1"
+    assert loop.subagents.model == "openai/gpt-4.1"
+    assert loop.consolidator.model == "openai/gpt-4.1"
+    assert loop.dream.model == "openai/gpt-4.1"
+
+
+@pytest.mark.asyncio
+async def test_model_command_switches_back_to_default(tmp_path) -> None:
+    loop = _make_loop(tmp_path)
+    loop.set_model_preset("fast")
+
+    out = await cmd_model(_ctx(loop, "/model default", args="default"))
+
+    assert "Switched model preset to `default`." in out.content
+    assert loop.model_preset == "default"
+    assert loop.model == "base-model"
+    assert loop.context_window_tokens == 1000
+
+
+@pytest.mark.asyncio
+async def test_model_command_unknown_preset_keeps_old_state(tmp_path) -> None:
+    loop = _make_loop(tmp_path)
+
+    out = await cmd_model(_ctx(loop, "/model missing", args="missing"))
+
+    assert "Could not switch model preset" in out.content
+    assert "Available presets: `default`, `fast`" in out.content
+    assert loop.model_preset is None
+    assert loop.model == "base-model"
+
+
+@pytest.mark.asyncio
+async def test_model_command_does_not_depend_on_my_allow_set(tmp_path) -> None:
+    loop = _make_loop(tmp_path)
+    assert loop.tools_config.my.allow_set is False
+
+    await cmd_model(_ctx(loop, "/model fast", args="fast"))
+
+    assert loop.model_preset == "fast"
+
+
+@pytest.mark.asyncio
+async def test_model_command_registered_as_exact_and_prefix(tmp_path) -> None:
+    router = CommandRouter()
+    register_builtin_commands(router)
+    loop = _make_loop(tmp_path)
+
+    out = await router.dispatch(_ctx(loop, "/model fast"))
+
+    assert out is not None
+    assert "Switched model preset" in out.content
+    assert loop.model_preset == "fast"
+
+
+def test_model_command_in_help_and_palette() -> None:
+    palette = builtin_command_palette()
+
+    assert any(item["command"] == "/model" and item["arg_hint"] == "[preset]" for item in palette)
+    assert "/model [preset]" in build_help_text()

tests/command/test_router_dispatchable.py

@@ -22,6 +22,7 @@ class TestIsDispatchableCommand:
     def test_exact_commands_match(self, router: CommandRouter) -> None:
         assert router.is_dispatchable_command("/new")
         assert router.is_dispatchable_command("/help")
+        assert router.is_dispatchable_command("/model")
         assert router.is_dispatchable_command("/dream")
         assert router.is_dispatchable_command("/dream-log")
         assert router.is_dispatchable_command("/dream-restore")
@@ -29,6 +30,7 @@ class TestIsDispatchableCommand:
     def test_prefix_commands_match(self, router: CommandRouter) -> None:
         assert router.is_dispatchable_command("/dream-log abc123")
         assert router.is_dispatchable_command("/dream-restore def456")
+        assert router.is_dispatchable_command("/model fast")
 
     def test_priority_commands_not_matched(self, router: CommandRouter) -> None:
         # Priority commands are NOT in the dispatchable tiers — they are