feat: add reasoning_effort configuration support for Doubao/GPT-5 models (#947)

* feat: Add reasoning effort configuration support

* Add `reasoning_effort` parameter to model config and agent initialization
* Support reasoning effort levels (minimal/low/medium/high) for Doubao/GPT-5 models
* Add UI controls in input box for reasoning effort selection
* Update doubao-seed-1.8 example config with reasoning effort support

Fixes & Cleanup:
* Ensure UTF-8 encoding for file operations
* Remove unused imports

* fix: set reasoning_effort to None for unsupported models

* fix: unit test error

* Update frontend/src/components/workspace/input-box.tsx

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
Co-authored-by: Willem Jiang <willem.jiang@gmail.com>

backend/src/config/app_config.py

@@ -72,7 +72,7 @@ class AppConfig(BaseModel):
             AppConfig: The loaded config.
         """
         resolved_path = cls.resolve_config_path(config_path)
-        with open(resolved_path) as f:
+        with open(resolved_path, encoding="utf-8") as f:
             config_data = yaml.safe_load(f)
         config_data = cls.resolve_env_variables(config_data)
 

backend/src/config/extensions_config.py

@@ -133,7 +133,7 @@ class ExtensionsConfig(BaseModel):
             # Return empty config if extensions config file is not found
             return cls(mcp_servers={}, skills={})
 
-        with open(resolved_path) as f:
+        with open(resolved_path, encoding="utf-8") as f:
             config_data = json.load(f)
 
         cls.resolve_env_variables(config_data)

backend/src/config/model_config.py

@@ -14,6 +14,7 @@ class ModelConfig(BaseModel):
     model: str = Field(..., description="Model name")
     model_config = ConfigDict(extra="allow")
     supports_thinking: bool = Field(default_factory=lambda: False, description="Whether the model supports thinking")
+    supports_reasoning_effort: bool = Field(default_factory=lambda: False, description="Whether the model supports reasoning effort")
     when_thinking_enabled: dict | None = Field(
         default_factory=lambda: None,
         description="Extra settings to be passed to the model when thinking is enabled",