Fix config file allowing partial overrides for judge/synthetic_user

src/mcprobe/config/__init__.py

@@ -5,6 +5,7 @@
     CLIOverrides,
     ConfigLoader,
     FileConfig,
+    FileLLMConfigOverride,
     MCPServerConfig,
     ResultsConfig,
     load_config,
@@ -15,6 +16,7 @@
     "CLIOverrides",
     "ConfigLoader",
     "FileConfig",
+    "FileLLMConfigOverride",
     "MCPServerConfig",
     "ResultsConfig",
     "load_config",

src/mcprobe/config/loader.py

@@ -95,13 +95,32 @@ class CLIOverrides(BaseModel):
     max_tokens: int | None = None
 
 
+class FileLLMConfigOverride(BaseModel):
+    """Partial LLM config for component-specific overrides in config file.
+
+    All fields are optional - only set values will override the shared llm config.
+    This allows users to set just extra_instructions for judge/synthetic_user
+    while inheriting provider, model, etc. from the shared llm section.
+    """
+
+    provider: str | None = None
+    model: str | None = None
+    temperature: float | None = Field(default=None, ge=0.0, le=2.0)
+    max_tokens: int | None = Field(default=None, ge=1)
+    api_key: SecretStr | None = None
+    base_url: str | None = None
+    context_size: int | None = Field(default=None, ge=1024)
+    reasoning: Literal["low", "medium", "high"] | None = None
+    extra_instructions: str | None = None
+
+
 class FileConfig(BaseModel):
     """Schema for mcprobe.yaml configuration file."""
 
     agent: AgentConfig = Field(default_factory=AgentConfig)
     llm: LLMConfig | None = None
-    judge: LLMConfig | None = None
-    synthetic_user: LLMConfig | None = None
+    judge: FileLLMConfigOverride | None = None
+    synthetic_user: FileLLMConfigOverride | None = None
     orchestrator: OrchestratorConfig = Field(default_factory=OrchestratorConfig)
     results: ResultsConfig = Field(default_factory=ResultsConfig)
     mcp_server: MCPServerConfig | None = None
@@ -244,6 +263,31 @@ def _apply_llm_config(source: LLMConfig, values: _ResolvedValues) -> None:
         if source.extra_instructions:
             values.extra_instructions.append(source.extra_instructions)
 
+    @staticmethod
+    def _apply_file_override(source: FileLLMConfigOverride, values: _ResolvedValues) -> None:
+        """Apply values from a file config override (mutates values in place).
+
+        Only non-None values are applied, allowing partial overrides.
+        """
+        if source.provider is not None:
+            values.provider = source.provider
+        if source.model is not None:
+            values.model = source.model
+        if source.temperature is not None:
+            values.temperature = source.temperature
+        if source.max_tokens is not None:
+            values.max_tokens = source.max_tokens
+        if source.base_url is not None:
+            values.base_url = source.base_url
+        if source.api_key:
+            values.api_key = source.api_key.get_secret_value()
+        if source.context_size is not None:
+            values.context_size = source.context_size
+        if source.reasoning is not None:
+            values.reasoning = source.reasoning
+        if source.extra_instructions:
+            values.extra_instructions.append(source.extra_instructions)
+
     @staticmethod
     def _apply_cli_overrides(cli: CLIOverrides, values: _ResolvedValues) -> None:
         """Apply CLI overrides to configuration values (mutates values in place)."""
@@ -322,12 +366,12 @@ def resolve_llm_config(
         if file_config and file_config.llm:
             ConfigLoader._apply_llm_config(file_config.llm, values)
 
-        # Apply component-specific config
-        component_config: LLMConfig | None = None
+        # Apply component-specific config (partial overrides)
+        component_config: FileLLMConfigOverride | None = None
         if file_config:
             component_config = getattr(file_config, component, None)
         if component_config:
-            ConfigLoader._apply_llm_config(component_config, values)
+            ConfigLoader._apply_file_override(component_config, values)
 
         # Apply scenario-level overrides
         if scenario_override:

tests/unit/test_config_loader.py

@@ -7,7 +7,14 @@
 import pytest
 from pydantic import SecretStr
 
-from mcprobe.config import AgentConfig, CLIOverrides, ConfigLoader, FileConfig, ResultsConfig
+from mcprobe.config import (
+    AgentConfig,
+    CLIOverrides,
+    ConfigLoader,
+    FileConfig,
+    FileLLMConfigOverride,
+    ResultsConfig,
+)
 from mcprobe.exceptions import ConfigurationError
 from mcprobe.models.config import LLMConfig, OrchestratorConfig
 
@@ -275,12 +282,13 @@ def test_component_overrides_shared(self) -> None:
         """Component-specific config overrides shared llm config."""
         file_config = FileConfig(
             llm=LLMConfig(provider="openai", model="gpt-4"),
-            judge=LLMConfig(provider="openai", model="gpt-4o"),
+            judge=FileLLMConfigOverride(model="gpt-4o"),
         )
 
         result = ConfigLoader.resolve_llm_config(file_config, "judge")
 
         assert result.model == "gpt-4o"
+        assert result.provider == "openai"  # Inherited from shared llm
 
     def test_cli_overrides_file_config(self) -> None:
         """CLI arguments override file config."""
@@ -322,14 +330,14 @@ def test_different_components_can_have_different_configs(self) -> None:
         """Judge and synthetic_user can have different configurations."""
         file_config = FileConfig(
             llm=LLMConfig(provider="openai", model="gpt-4"),
-            judge=LLMConfig(provider="openai", model="gpt-4o"),
-            synthetic_user=LLMConfig(provider="ollama", model="llama3.2"),
+            judge=FileLLMConfigOverride(model="gpt-4o"),
+            synthetic_user=FileLLMConfigOverride(provider="ollama", model="llama3.2"),
         )
 
         judge_config = ConfigLoader.resolve_llm_config(file_config, "judge")
         user_config = ConfigLoader.resolve_llm_config(file_config, "synthetic_user")
 
-        assert judge_config.provider == "openai"
+        assert judge_config.provider == "openai"  # Inherited from shared llm
         assert judge_config.model == "gpt-4o"
         assert user_config.provider == "ollama"
         assert user_config.model == "llama3.2"