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feat(runner): support fallback candidates

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Resolve fallbackModels as preset references or explicit inline provider configs so failover uses complete model settings without exposing fallback logic to the agent loop.

Co-authored-by: Cursor <cursoragent@cursor.com>
This commit is contained in:
Xubin Ren
2026-05-13 15:34:03 +00:00
co-authored by Cursor
parent 43db848db0
commit 5efd67919b
5 changed files with 502 additions and 59 deletions
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tests/agent/test_runner_fallback.py
+285 -36
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@@ -3,10 +3,11 @@
from __future__ import annotations
from typing import Any
from unittest.mock import MagicMock
from unittest.mock import MagicMock, patch
import pytest
from nanobot.config.schema import ModelPresetConfig
from nanobot.providers.base import LLMProvider, LLMResponse
from nanobot.providers.fallback_provider import FallbackProvider
@@ -16,14 +17,45 @@ def _make_response(
finish_reason: str = "stop",
*,
error_kind: str | None = None,
error_status_code: int | None = None,
error_type: str | None = None,
error_code: str | None = None,
error_should_retry: bool | None = None,
) -> LLMResponse:
return LLMResponse(content=content, finish_reason=finish_reason, error_kind=error_kind)
return LLMResponse(
content=content,
finish_reason=finish_reason,
error_kind=error_kind,
error_status_code=error_status_code,
error_type=error_type,
error_code=error_code,
error_should_retry=error_should_retry,
)
def _error_response(content: str = "api error") -> LLMResponse:
return _make_response(content, finish_reason="error", error_kind="server_error")
def _fallback(
model: str,
provider: str = "custom",
*,
max_tokens: int = 8192,
context_window_tokens: int = 65_536,
temperature: float = 0.1,
reasoning_effort: str | None = None,
) -> ModelPresetConfig:
return ModelPresetConfig(
model=model,
provider=provider,
max_tokens=max_tokens,
context_window_tokens=context_window_tokens,
temperature=temperature,
reasoning_effort=reasoning_effort,
)
class _FakeProvider(LLMProvider):
"""Fake provider for testing."""
@@ -53,24 +85,163 @@ class _FakeProvider(LLMProvider):
def test_fallback_models_default_empty() -> None:
from nanobot.config.schema import ModelPresetConfig
p = ModelPresetConfig(model="test/model")
assert p.fallback_models == []
from nanobot.config.schema import AgentDefaults
defaults = AgentDefaults()
assert defaults.fallback_models == []
def test_fallback_models_accepts_list() -> None:
from nanobot.config.schema import ModelPresetConfig
p = ModelPresetConfig(model="test/primary", fallback_models=["test/a", "test/b"])
assert p.fallback_models == ["test/a", "test/b"]
def test_fallback_models_accept_preset_refs_and_inline_configs() -> None:
from nanobot.config.schema import Config, InlineFallbackConfig
def test_fallback_models_from_camel_case() -> None:
from nanobot.config.schema import ModelPresetConfig
p = ModelPresetConfig.model_validate({
"model": "test/primary",
"fallbackModels": ["test/a"],
config = Config.model_validate({
"agents": {
"defaults": {
"fallbackModels": [
"deep",
{
"provider": "openai",
"model": "gpt-4.1",
"maxTokens": 4096,
},
]
}
},
"modelPresets": {
"deep": {"provider": "anthropic", "model": "claude-opus-4-7"}
},
})
assert p.fallback_models == ["test/a"]
assert config.agents.defaults.fallback_models[0] == "deep"
assert config.agents.defaults.fallback_models[1] == InlineFallbackConfig(
provider="openai",
model="gpt-4.1",
max_tokens=4096,
)
def test_fallback_model_preset_ref_must_exist() -> None:
from nanobot.config.schema import Config
with pytest.raises(ValueError, match="fallback_models.*not found"):
Config.model_validate({
"agents": {"defaults": {"fallbackModels": ["missing"]}},
"modelPresets": {},
})
def test_provider_signature_tracks_fallback_presets_and_provider_config() -> None:
from nanobot.config.schema import Config
from nanobot.providers.factory import provider_signature
base = {
"agents": {
"defaults": {
"modelPreset": "fast",
"fallbackModels": ["deep"],
}
},
"modelPresets": {
"fast": {"model": "openai/gpt-4.1", "provider": "openai"},
"deep": {"model": "anthropic/claude-sonnet-4-6", "provider": "anthropic"},
},
"providers": {
"openai": {"apiKey": "primary-key"},
"anthropic": {"apiKey": "fallback-key"},
},
}
changed_fallback = {
**base,
"agents": {"defaults": {"modelPreset": "fast", "fallbackModels": ["backup"]}},
"modelPresets": {
**base["modelPresets"],
"backup": {"model": "deepseek/deepseek-chat", "provider": "deepseek"},
},
"providers": {
**base["providers"],
"deepseek": {"apiKey": "deepseek-key"},
},
}
changed_key = {
**base,
"providers": {
"openai": {"apiKey": "primary-key"},
"anthropic": {"apiKey": "new-fallback-key"},
},
}
signature = provider_signature(Config.model_validate(base))
assert signature != provider_signature(Config.model_validate(changed_fallback))
assert signature != provider_signature(Config.model_validate(changed_key))
def test_provider_snapshot_uses_smallest_fallback_context_window() -> None:
from nanobot.config.schema import Config
from nanobot.providers.factory import build_provider_snapshot
config = Config.model_validate({
"agents": {
"defaults": {
"modelPreset": "fast",
"fallbackModels": ["deep"],
}
},
"modelPresets": {
"fast": {
"model": "openai/gpt-4.1",
"provider": "openai",
"contextWindowTokens": 128000,
},
"deep": {
"model": "deepseek/deepseek-chat",
"provider": "deepseek",
"contextWindowTokens": 64000,
},
},
"providers": {
"openai": {"apiKey": "primary-key"},
"deepseek": {"apiKey": "fallback-key"},
},
})
with patch("nanobot.providers.openai_compat_provider.AsyncOpenAI"):
snapshot = build_provider_snapshot(config)
assert snapshot.context_window_tokens == 64000
def test_inline_fallback_reasoning_effort_does_not_inherit_primary() -> None:
from nanobot.config.schema import Config
from nanobot.providers.factory import provider_signature
config = Config.model_validate({
"agents": {
"defaults": {
"modelPreset": "fast",
"fallbackModels": [
{"provider": "openai", "model": "gpt-4.1"}
],
}
},
"modelPresets": {
"fast": {
"model": "anthropic/claude-opus-4-5",
"provider": "anthropic",
"reasoningEffort": "high",
}
},
"providers": {
"anthropic": {"apiKey": "primary-key"},
"openai": {"apiKey": "fallback-key"},
},
})
signature = provider_signature(config)
fallback_signatures = signature[-1]
assert fallback_signatures[0][11] is None
# -- FallbackProvider tests --
@@ -83,7 +254,7 @@ class TestNoFallbackWhenPrimarySucceeds:
factory = MagicMock()
fb = FallbackProvider(
primary=primary,
fallback_models=["fallback-a"],
fallback_presets=[_fallback("fallback-a")],
provider_factory=factory,
)
@@ -102,14 +273,14 @@ class TestFallbackOnPrimaryError:
fb = FallbackProvider(
primary=primary,
fallback_models=["fallback-a"],
fallback_presets=[_fallback("fallback-a")],
provider_factory=factory,
)
result = await fb.chat(messages=[{"role": "user", "content": "hi"}], model="primary-model")
assert result.content == "fallback ok"
assert result.finish_reason == "stop"
factory.assert_called_once_with("fallback-a")
factory.assert_called_once_with(_fallback("fallback-a"))
assert primary.chat_calls[0]["model"] == "primary-model"
assert fallback.chat_calls[0]["model"] == "fallback-a"
@@ -121,7 +292,7 @@ class TestNoFallbackWhenContentStreamed:
factory = MagicMock()
fb = FallbackProvider(
primary=primary,
fallback_models=["fallback-a"],
fallback_presets=[_fallback("fallback-a")],
provider_factory=factory,
)
@@ -146,14 +317,62 @@ class TestFailoverOnTransientError:
factory = MagicMock(return_value=fallback)
fb = FallbackProvider(
primary=primary,
fallback_models=["fallback-a"],
fallback_presets=[_fallback("fallback-a")],
provider_factory=factory,
)
result = await fb.chat(messages=[{"role": "user", "content": "hi"}])
assert result.content == "fallback ok"
assert result.finish_reason == "stop"
factory.assert_called_once_with("fallback-a")
factory.assert_called_once_with(_fallback("fallback-a"))
class TestNoFallbackOnNonRetryableError:
@pytest.mark.asyncio
async def test_bad_request(self) -> None:
primary = _FakeProvider(
"primary",
_make_response(
"invalid request",
finish_reason="error",
error_status_code=400,
error_kind="invalid_request",
),
)
factory = MagicMock()
fb = FallbackProvider(
primary=primary,
fallback_presets=[_fallback("fallback-a")],
provider_factory=factory,
)
result = await fb.chat(messages=[{"role": "user", "content": "hi"}])
assert result.finish_reason == "error"
factory.assert_not_called()
@pytest.mark.asyncio
async def test_auth_error(self) -> None:
primary = _FakeProvider(
"primary",
_make_response(
"unauthorized",
finish_reason="error",
error_status_code=401,
error_kind="authentication",
),
)
factory = MagicMock()
fb = FallbackProvider(
primary=primary,
fallback_presets=[_fallback("fallback-a")],
provider_factory=factory,
)
result = await fb.chat(messages=[{"role": "user", "content": "hi"}])
assert result.finish_reason == "error"
factory.assert_not_called()
@pytest.mark.asyncio
async def test_timeout(self) -> None:
@@ -165,14 +384,14 @@ class TestFailoverOnTransientError:
factory = MagicMock(return_value=fallback)
fb = FallbackProvider(
primary=primary,
fallback_models=["fallback-a"],
fallback_presets=[_fallback("fallback-a")],
provider_factory=factory,
)
result = await fb.chat(messages=[{"role": "user", "content": "hi"}])
assert result.content == "fallback ok"
assert result.finish_reason == "stop"
factory.assert_called_once_with("fallback-a")
factory.assert_called_once_with(_fallback("fallback-a"))
class TestFallbackTriesModelsInOrder:
@@ -185,15 +404,15 @@ class TestFallbackTriesModelsInOrder:
fb = FallbackProvider(
primary=primary,
fallback_models=["fallback-a", "fallback-b"],
fallback_presets=[_fallback("fallback-a"), _fallback("fallback-b")],
provider_factory=factory,
)
result = await fb.chat(messages=[{"role": "user", "content": "hi"}])
assert result.content == "b ok"
assert factory.call_count == 2
factory.assert_any_call("fallback-a")
factory.assert_any_call("fallback-b")
factory.assert_any_call(_fallback("fallback-a"))
factory.assert_any_call(_fallback("fallback-b"))
class TestAllFallbacksFail:
@@ -205,7 +424,7 @@ class TestAllFallbacksFail:
fb = FallbackProvider(
primary=primary,
fallback_models=["fallback-a"],
fallback_presets=[_fallback("fallback-a")],
provider_factory=factory,
)
@@ -223,7 +442,7 @@ class TestFactoryExceptionSkipsModel:
fb = FallbackProvider(
primary=primary,
fallback_models=["fallback-a", "fallback-b"],
fallback_presets=[_fallback("fallback-a"), _fallback("fallback-b")],
provider_factory=factory,
)
@@ -242,13 +461,43 @@ class TestFallbackModelParameter:
fb = FallbackProvider(
primary=primary,
fallback_models=["fallback-model"],
fallback_presets=[_fallback("fallback-model")],
provider_factory=factory,
)
await fb.chat(messages=[{"role": "user", "content": "hi"}], model="primary-model")
assert fallback.chat_calls[0]["model"] == "fallback-model"
@pytest.mark.asyncio
async def test_uses_fallback_generation_fields(self) -> None:
primary = _FakeProvider("primary", _error_response())
fallback = _FakeProvider("fallback", _make_response("ok"))
fb = FallbackProvider(
primary=primary,
fallback_presets=[
_fallback(
"fallback-model",
max_tokens=1234,
temperature=0.4,
reasoning_effort=None,
)
],
provider_factory=MagicMock(return_value=fallback),
)
await fb.chat(
messages=[{"role": "user", "content": "hi"}],
model="primary-model",
max_tokens=8192,
temperature=0.1,
reasoning_effort="high",
)
assert fallback.chat_calls[0]["model"] == "fallback-model"
assert fallback.chat_calls[0]["max_tokens"] == 1234
assert fallback.chat_calls[0]["temperature"] == 0.4
assert "reasoning_effort" not in fallback.chat_calls[0]
class TestNoFallbackWhenEmptyList:
@pytest.mark.asyncio
@@ -258,7 +507,7 @@ class TestNoFallbackWhenEmptyList:
fb = FallbackProvider(
primary=primary,
fallback_models=[],
fallback_presets=[],
provider_factory=factory,
)
@@ -277,7 +526,7 @@ class TestChatStreamFailover:
fb = FallbackProvider(
primary=primary,
fallback_models=["fallback-a"],
fallback_presets=[_fallback("fallback-a")],
provider_factory=factory,
)
@@ -291,7 +540,7 @@ class TestGetDefaultModel:
primary = _FakeProvider("primary")
fb = FallbackProvider(
primary=primary,
fallback_models=["a"],
fallback_presets=[_fallback("a")],
provider_factory=MagicMock(),
)
assert fb.get_default_model() == "primary/model"
@@ -305,7 +554,7 @@ class TestCircuitBreaker:
factory = MagicMock(return_value=fallback)
fb = FallbackProvider(
primary=primary,
fallback_models=["fallback-a"],
fallback_presets=[_fallback("fallback-a")],
provider_factory=factory,
)
@@ -329,7 +578,7 @@ class TestCircuitBreaker:
factory = MagicMock(return_value=fallback)
fb = FallbackProvider(
primary=primary,
fallback_models=["fallback-a"],
fallback_presets=[_fallback("fallback-a")],
provider_factory=factory,
)
@@ -357,7 +606,7 @@ class TestGenerationForwarded:
primary.generation = GenerationSettings(temperature=0.5, max_tokens=1024)
fb = FallbackProvider(
primary=primary,
fallback_models=["a"],
fallback_presets=[_fallback("a")],
provider_factory=MagicMock(),
)
assert fb.generation.temperature == 0.5