refactor(providers): move provider snapshot creation into factory

nanobot/providers/factory.py

@@ -0,0 +1,112 @@
+"""Create LLM providers from config."""
+
+from __future__ import annotations
+
+from dataclasses import dataclass
+from pathlib import Path
+
+from nanobot.config.schema import Config
+from nanobot.providers.base import GenerationSettings, LLMProvider
+from nanobot.providers.registry import find_by_name
+
+
+@dataclass(frozen=True)
+class ProviderSnapshot:
+    provider: LLMProvider
+    model: str
+    context_window_tokens: int
+    signature: tuple[object, ...]
+
+
+def make_provider(config: Config) -> LLMProvider:
+    """Create the LLM provider implied by config."""
+    model = config.agents.defaults.model
+    provider_name = config.get_provider_name(model)
+    p = config.get_provider(model)
+    spec = find_by_name(provider_name) if provider_name else None
+    backend = spec.backend if spec else "openai_compat"
+
+    if backend == "azure_openai":
+        if not p or not p.api_key or not p.api_base:
+            raise ValueError("Azure OpenAI requires api_key and api_base in config.")
+    elif backend == "openai_compat" and not model.startswith("bedrock/"):
+        needs_key = not (p and p.api_key)
+        exempt = spec and (spec.is_oauth or spec.is_local or spec.is_direct)
+        if needs_key and not exempt:
+            raise ValueError(f"No API key configured for provider '{provider_name}'.")
+
+    if backend == "openai_codex":
+        from nanobot.providers.openai_codex_provider import OpenAICodexProvider
+
+        provider = OpenAICodexProvider(default_model=model)
+    elif backend == "azure_openai":
+        from nanobot.providers.azure_openai_provider import AzureOpenAIProvider
+
+        provider = AzureOpenAIProvider(
+            api_key=p.api_key,
+            api_base=p.api_base,
+            default_model=model,
+        )
+    elif backend == "github_copilot":
+        from nanobot.providers.github_copilot_provider import GitHubCopilotProvider
+
+        provider = GitHubCopilotProvider(default_model=model)
+    elif backend == "anthropic":
+        from nanobot.providers.anthropic_provider import AnthropicProvider
+
+        provider = AnthropicProvider(
+            api_key=p.api_key if p else None,
+            api_base=config.get_api_base(model),
+            default_model=model,
+            extra_headers=p.extra_headers if p else None,
+        )
+    else:
+        from nanobot.providers.openai_compat_provider import OpenAICompatProvider
+
+        provider = OpenAICompatProvider(
+            api_key=p.api_key if p else None,
+            api_base=config.get_api_base(model),
+            default_model=model,
+            extra_headers=p.extra_headers if p else None,
+            spec=spec,
+        )
+
+    defaults = config.agents.defaults
+    provider.generation = GenerationSettings(
+        temperature=defaults.temperature,
+        max_tokens=defaults.max_tokens,
+        reasoning_effort=defaults.reasoning_effort,
+    )
+    return provider
+
+
+def provider_signature(config: Config) -> tuple[object, ...]:
+    """Return the config fields that affect the primary LLM provider."""
+    model = config.agents.defaults.model
+    defaults = config.agents.defaults
+    return (
+        model,
+        defaults.provider,
+        config.get_provider_name(model),
+        config.get_api_key(model),
+        config.get_api_base(model),
+        defaults.max_tokens,
+        defaults.temperature,
+        defaults.reasoning_effort,
+        defaults.context_window_tokens,
+    )
+
+
+def build_provider_snapshot(config: Config) -> ProviderSnapshot:
+    return ProviderSnapshot(
+        provider=make_provider(config),
+        model=config.agents.defaults.model,
+        context_window_tokens=config.agents.defaults.context_window_tokens,
+        signature=provider_signature(config),
+    )
+
+
+def load_provider_snapshot(config_path: Path | 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)))