refactor: thread app_config through lead and subagent task path (#2666)

* refactor: thread app config through lead prompt

* fix: honor explicit app config across runtime paths

* style: format subagent executor tests

* fix: thread resolved app config and guard subagents-only fallback

Address two PR review findings:

1. _create_summarization_middleware passed the original (possibly None)
   app_config into create_chat_model, forcing the model factory back to
   ambient get_app_config() and risking config drift between the
   middleware's resolved view and the model's view. Pass the resolved
   AppConfig instance through end-to-end.

2. get_available_subagent_names accepted Any-typed config and forwarded
   it to is_host_bash_allowed, which reads ``.sandbox``. A
   SubagentsAppConfig (also accepted upstream as a sum-type input) has
   no ``.sandbox`` attribute and would be silently treated as "no
   sandbox configured", incorrectly disabling the bash subagent. Guard
   on hasattr and fall back to ambient lookup otherwise.

Adds regression tests for both paths.

* chore: simplify hasattr guard and tighten regression tests

- Collapse if/else into ternary in get_available_subagent_names; hasattr(None, ...) is False so the explicit None check was redundant.
- Drop comments that narrate the change rather than explain non-obvious WHY (test names already convey intent).
- Replace stringly-typed sentinel "no-arg" in regression test with direct args tuple comparison.

---------

Co-authored-by: greatmengqi <chenmengqi.0376@bytedance.com>

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

@@ -4,7 +4,7 @@ import asyncio
 import logging
 import uuid
 from dataclasses import replace
-from typing import Annotated
+from typing import TYPE_CHECKING, Annotated, Any, cast
 
 from langchain.tools import InjectedToolCallId, ToolRuntime, tool
 from langgraph.config import get_stream_writer
@@ -22,9 +22,21 @@ from deerflow.subagents.executor import (
     request_cancel_background_task,
 )
 
+if TYPE_CHECKING:
+    from deerflow.config.app_config import AppConfig
+
 logger = logging.getLogger(__name__)
 
 
+def _get_runtime_app_config(runtime: Any) -> "AppConfig | None":
+    context = getattr(runtime, "context", None)
+    if isinstance(context, dict):
+        app_config = context.get("app_config")
+        if app_config is not None:
+            return cast("AppConfig", app_config)
+    return None
+
+
 def _merge_skill_allowlists(parent: list[str] | None, child: list[str] | None) -> list[str] | None:
     """Return the effective subagent skill allowlist under the parent policy."""
     if parent is None:
@@ -81,15 +93,18 @@ async def task_tool(
         subagent_type: The type of subagent to use. ALWAYS PROVIDE THIS PARAMETER THIRD.
         max_turns: Optional maximum number of agent turns. Defaults to subagent's configured max.
     """
-    available_subagent_names = get_available_subagent_names()
+    runtime_app_config = _get_runtime_app_config(runtime)
+    available_subagent_names = get_available_subagent_names(app_config=runtime_app_config) if runtime_app_config is not None else get_available_subagent_names()
 
     # Get subagent configuration
-    config = get_subagent_config(subagent_type)
+    config = get_subagent_config(subagent_type, app_config=runtime_app_config) if runtime_app_config is not None else get_subagent_config(subagent_type)
     if config is None:
         available = ", ".join(available_subagent_names)
         return f"Error: Unknown subagent type '{subagent_type}'. Available: {available}"
-    if subagent_type == "bash" and not is_host_bash_allowed():
-        return f"Error: {LOCAL_BASH_SUBAGENT_DISABLED_MESSAGE}"
+    if subagent_type == "bash":
+        host_bash_allowed = is_host_bash_allowed(runtime_app_config) if runtime_app_config is not None else is_host_bash_allowed()
+        if not host_bash_allowed:
+            return f"Error: {LOCAL_BASH_SUBAGENT_DISABLED_MESSAGE}"
 
     # Build config overrides
     overrides: dict = {}
@@ -136,25 +151,34 @@ 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)
+    resolved_app_config = runtime_app_config
+    if config.model == "inherit" and parent_model is None and resolved_app_config is None:
+        resolved_app_config = get_app_config()
+    effective_model = resolve_subagent_model_name(config, parent_model, app_config=resolved_app_config)
 
     # Subagents should not have subagent tools enabled (prevent recursive nesting)
-    tools = get_available_tools(model_name=effective_model, groups=parent_tool_groups, subagent_enabled=False)
+    available_tools_kwargs = {
+        "model_name": effective_model,
+        "groups": parent_tool_groups,
+        "subagent_enabled": False,
+    }
+    if resolved_app_config is not None:
+        available_tools_kwargs["app_config"] = resolved_app_config
+    tools = get_available_tools(**available_tools_kwargs)
 
     # Create executor
-    executor = SubagentExecutor(
-        config=config,
-        tools=tools,
-        app_config=app_config,
-        parent_model=parent_model,
-        sandbox_state=sandbox_state,
-        thread_data=thread_data,
-        thread_id=thread_id,
-        trace_id=trace_id,
-    )
+    executor_kwargs = {
+        "config": config,
+        "tools": tools,
+        "parent_model": parent_model,
+        "sandbox_state": sandbox_state,
+        "thread_data": thread_data,
+        "thread_id": thread_id,
+        "trace_id": trace_id,
+    }
+    if resolved_app_config is not None:
+        executor_kwargs["app_config"] = resolved_app_config
+    executor = SubagentExecutor(**executor_kwargs)
 
     # Start background execution (always async to prevent blocking)
     # Use tool_call_id as task_id for better traceability
@@ -189,11 +213,12 @@ async def task_tool(
                 last_status = result.status
 
             # Check for new AI messages and send task_running events
-            current_message_count = len(result.ai_messages)
+            ai_messages = result.ai_messages or []
+            current_message_count = len(ai_messages)
             if current_message_count > last_message_count:
                 # Send task_running event for each new message
                 for i in range(last_message_count, current_message_count):
-                    message = result.ai_messages[i]
+                    message = ai_messages[i]
                     writer(
                         {
                             "type": "task_running",