fix(subagents): use model override for tools and middleware (#2641)

* fix(subagents): use model override for tools and middleware

* fix(config): resolve effective subagent model

* fix(subagents): defer app config loading

* fix(subagents): fully defer config.yaml load in executor __init__

The previous attempt only relocated the explicit get_app_config() call,
but left resolve_subagent_model_name(...) running eagerly in __init__.
That helper has its own internal get_app_config() fallback, which still
fired when both app_config and parent_model were None and
config.model == "inherit" — exactly the path unit tests hit, breaking
21 tests in CI with FileNotFoundError: config.yaml.

Skip the eager resolve in __init__ when it would require loading the
config file, and defer to _create_agent (which already has the
app_config or get_app_config() fallback).

backend/packages/harness/deerflow/agents/middlewares/tool_error_handling_middleware.py

@@ -136,11 +136,32 @@ def build_lead_runtime_middlewares(*, app_config: AppConfig, lazy_init: bool = T
     )
 
 
-def build_subagent_runtime_middlewares(*, app_config: AppConfig, lazy_init: bool = True) -> list[AgentMiddleware]:
+def build_subagent_runtime_middlewares(
+    *,
+    app_config: AppConfig | None = None,
+    model_name: str | None = None,
+    lazy_init: bool = True,
+) -> list[AgentMiddleware]:
     """Middlewares shared by subagent runtime before subagent-only middlewares."""
-    return _build_runtime_middlewares(
+    if app_config is None:
+        from deerflow.config import get_app_config
+
+        app_config = get_app_config()
+
+    middlewares = _build_runtime_middlewares(
         app_config=app_config,
         include_uploads=False,
         include_dangling_tool_call_patch=True,
         lazy_init=lazy_init,
     )
+
+    if model_name is None and app_config.models:
+        model_name = app_config.models[0].name
+
+    model_config = app_config.get_model_config(model_name) if model_name else None
+    if model_config is not None and model_config.supports_vision:
+        from deerflow.agents.middlewares.view_image_middleware import ViewImageMiddleware
+
+        middlewares.append(ViewImageMiddleware())
+
+    return middlewares

backend/packages/harness/deerflow/subagents/config.py

@@ -1,6 +1,10 @@
 """Subagent configuration definitions."""
 
 from dataclasses import dataclass, field
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    from deerflow.config.app_config import AppConfig
 
 
 @dataclass
@@ -29,3 +33,24 @@ class SubagentConfig:
     model: str = "inherit"
     max_turns: int = 50
     timeout_seconds: int = 900
+
+
+def _default_model_name(app_config: "AppConfig") -> str:
+    if not app_config.models:
+        raise ValueError("No chat models are configured. Please configure at least one model in config.yaml.")
+    return app_config.models[0].name
+
+
+def resolve_subagent_model_name(config: SubagentConfig, parent_model: str | None, *, app_config: "AppConfig | None" = None) -> str:
+    """Resolve the effective model name a subagent should use."""
+    if config.model != "inherit":
+        return config.model
+
+    if parent_model is not None:
+        return parent_model
+
+    if app_config is None:
+        from deerflow.config import get_app_config
+
+        app_config = get_app_config()
+    return _default_model_name(app_config)

backend/packages/harness/deerflow/subagents/executor.py

@@ -20,9 +20,10 @@ from langchain_core.messages import AIMessage, HumanMessage, SystemMessage
 from langchain_core.runnables import RunnableConfig
 
 from deerflow.agents.thread_state import SandboxState, ThreadDataState, ThreadState
+from deerflow.config import get_app_config
 from deerflow.config.app_config import AppConfig
 from deerflow.models import create_chat_model
-from deerflow.subagents.config import SubagentConfig
+from deerflow.subagents.config import SubagentConfig, resolve_subagent_model_name
 
 logger = logging.getLogger(__name__)
 
@@ -213,21 +214,6 @@ def _filter_tools(
     return filtered
 
 
-def _get_model_name(config: SubagentConfig, parent_model: str | None) -> str | None:
-    """Resolve the model name for a subagent.
-
-    Args:
-        config: Subagent configuration.
-        parent_model: The parent agent's model name.
-
-    Returns:
-        Model name to use, or None to use default.
-    """
-    if config.model == "inherit":
-        return parent_model
-    return config.model
-
-
 class SubagentExecutor:
     """Executor for running subagents."""
 
@@ -247,9 +233,9 @@ class SubagentExecutor:
         Args:
             config: Subagent configuration.
             tools: List of all available tools (will be filtered).
-            app_config: Resolved AppConfig; threaded into middleware factories
-                at agent-build time. When None, ``_create_agent`` falls back to
-                ``get_app_config()`` (matches the lead-agent factory's pattern).
+            app_config: Resolved AppConfig. When None, ``_create_agent`` falls
+                back to ``get_app_config()`` (matches the lead-agent factory's
+                pattern).
             parent_model: The parent agent's model name for inheritance.
             sandbox_state: Sandbox state from parent agent.
             thread_data: Thread data from parent agent.
@@ -259,6 +245,13 @@ class SubagentExecutor:
         self.config = config
         self.app_config = app_config
         self.parent_model = parent_model
+        # Resolve eagerly only when it does not require loading config.yaml; otherwise defer
+        # to _create_agent (which already loads app_config) so unit tests can construct
+        # executors without a config file present.
+        if config.model != "inherit" or parent_model is not None or app_config is not None:
+            self.model_name: str | None = resolve_subagent_model_name(config, parent_model, app_config=app_config)
+        else:
+            self.model_name = None
         self.sandbox_state = sandbox_state
         self.thread_data = thread_data
         self.thread_id = thread_id
@@ -276,17 +269,15 @@ class SubagentExecutor:
 
     def _create_agent(self):
         """Create the agent instance."""
-        # Mirror lead-agent factory pattern: prefer explicit app_config,
-        # fall back to ambient lookup at agent-build time.
-        from deerflow.config import get_app_config
-
-        resolved_app_config = self.app_config or get_app_config()
-        model_name = _get_model_name(self.config, self.parent_model)
-        model = create_chat_model(name=model_name, thinking_enabled=False, app_config=resolved_app_config)
+        app_config = self.app_config or get_app_config()
+        if self.model_name is None:
+            self.model_name = resolve_subagent_model_name(self.config, self.parent_model, app_config=app_config)
+        model = create_chat_model(name=self.model_name, thinking_enabled=False, app_config=app_config)
 
         from deerflow.agents.middlewares.tool_error_handling_middleware import build_subagent_runtime_middlewares
 
-        middlewares = build_subagent_runtime_middlewares(app_config=resolved_app_config, lazy_init=True)
+        # Reuse shared middleware composition with lead agent.
+        middlewares = build_subagent_runtime_middlewares(app_config=app_config, model_name=self.model_name, lazy_init=True)
 
         return create_agent(
             model=model,

backend/packages/harness/deerflow/tools/builtins/task_tool.py

@@ -11,9 +11,16 @@ from langgraph.config import get_stream_writer
 from langgraph.typing import ContextT
 
 from deerflow.agents.thread_state import ThreadState
+from deerflow.config import get_app_config
 from deerflow.sandbox.security import LOCAL_BASH_SUBAGENT_DISABLED_MESSAGE, is_host_bash_allowed
 from deerflow.subagents import SubagentExecutor, get_available_subagent_names, get_subagent_config
-from deerflow.subagents.executor import SubagentStatus, cleanup_background_task, get_background_task_result, request_cancel_background_task
+from deerflow.subagents.config import resolve_subagent_model_name
+from deerflow.subagents.executor import (
+    SubagentStatus,
+    cleanup_background_task,
+    get_background_task_result,
+    request_cancel_background_task,
+)
 
 logger = logging.getLogger(__name__)
 
@@ -129,14 +136,19 @@ async def task_tool(
 
     # Inherit parent agent's tool_groups so subagents respect the same restrictions
     parent_tool_groups = metadata.get("tool_groups")
+    app_config = None
+    if config.model == "inherit" and parent_model is None:
+        app_config = get_app_config()
+    effective_model = resolve_subagent_model_name(config, parent_model, app_config=app_config)
 
     # Subagents should not have subagent tools enabled (prevent recursive nesting)
-    tools = get_available_tools(model_name=parent_model, groups=parent_tool_groups, subagent_enabled=False)
+    tools = get_available_tools(model_name=effective_model, groups=parent_tool_groups, subagent_enabled=False)
 
     # Create executor
     executor = SubagentExecutor(
         config=config,
         tools=tools,
+        app_config=app_config,
         parent_model=parent_model,
         sandbox_state=sandbox_state,
         thread_data=thread_data,