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/runtime/runs/worker.py

@@ -21,7 +21,7 @@ import inspect
 import logging
 from dataclasses import dataclass, field
 from functools import lru_cache
-from typing import TYPE_CHECKING, Any, Literal
+from typing import TYPE_CHECKING, Any, Literal, cast
 
 if TYPE_CHECKING:
     from langchain_core.messages import HumanMessage
@@ -39,12 +39,19 @@ logger = logging.getLogger(__name__)
 _VALID_LG_MODES = {"values", "updates", "checkpoints", "tasks", "debug", "messages", "custom"}
 
 
-def _build_runtime_context(thread_id: str, run_id: str, caller_context: Any | None) -> dict[str, Any]:
+def _build_runtime_context(
+    thread_id: str,
+    run_id: str,
+    caller_context: Any | None,
+    app_config: AppConfig | None = None,
+) -> dict[str, Any]:
     """Build the dict that becomes ``ToolRuntime.context`` for the run.
 
     Always includes ``thread_id`` and ``run_id``. Additional keys from the caller's
     ``config['context']`` (e.g. ``agent_name`` for the bootstrap flow — issue #2677)
-    are merged in but never override ``thread_id``/``run_id``.
+    are merged in but never override ``thread_id``/``run_id``. The resolved
+    ``AppConfig`` is added by the worker so tools can consume it without ambient
+    global lookups.
 
     langgraph 1.1+ surfaces this as ``runtime.context`` via the parent runtime stored
     under ``config['configurable']['__pregel_runtime']`` — see
@@ -54,6 +61,8 @@ def _build_runtime_context(thread_id: str, run_id: str, caller_context: Any | No
     if isinstance(caller_context, dict):
         for key, value in caller_context.items():
             runtime_ctx.setdefault(key, value)
+    if app_config is not None:
+        runtime_ctx["app_config"] = app_config
     return runtime_ctx
 
 
@@ -74,6 +83,18 @@ class RunContext:
     app_config: AppConfig | None = field(default=None)
 
 
+def _install_runtime_context(config: dict, runtime_context: dict[str, Any]) -> None:
+    existing_context = config.get("context")
+    if isinstance(existing_context, dict):
+        existing_context.setdefault("thread_id", runtime_context["thread_id"])
+        existing_context.setdefault("run_id", runtime_context["run_id"])
+        if "app_config" in runtime_context:
+            existing_context["app_config"] = runtime_context["app_config"]
+        return
+
+    config["context"] = dict(runtime_context)
+
+
 def _compute_agent_factory_supports_app_config(agent_factory: Any) -> bool:
     try:
         return "app_config" in inspect.signature(agent_factory).parameters
@@ -191,11 +212,9 @@ async def run_agent(
         # access thread-level data. langgraph-cli does this automatically; we must do it
         # manually here because we drive the graph through ``agent.astream(config=...)``
         # without passing the official ``context=`` parameter.
-        runtime_ctx = _build_runtime_context(thread_id, run_id, config.get("context"))
-        if "context" in config and isinstance(config["context"], dict):
-            config["context"].setdefault("thread_id", thread_id)
-            config["context"].setdefault("run_id", run_id)
-        runtime = Runtime(context=runtime_ctx, store=store)
+        runtime_ctx = _build_runtime_context(thread_id, run_id, config.get("context"), ctx.app_config)
+        _install_runtime_context(config, runtime_ctx)
+        runtime = Runtime(context=cast(Any, runtime_ctx), store=store)
         config.setdefault("configurable", {})["__pregel_runtime"] = runtime
 
         # Inject RunJournal as a LangChain callback handler.