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