refactor(backend): consolidate thread_id resolution into shared get_thread_id() utility (#2522)

Extract duplicated thread_id fallback logic from 11 files into a single
  deerflow.utils.runtime.get_thread_id() function with a documented 3-level
  cascade (runtime.context → runtime.config → get_config()).

  The module docstring also clarifies the __pregel_runtime injection pattern used in
  gateway mode.

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

@@ -3,33 +3,16 @@ from typing import Annotated
 
 from langchain.tools import InjectedToolCallId, ToolRuntime, tool
 from langchain_core.messages import ToolMessage
-from langgraph.config import get_config
 from langgraph.types import Command
 from langgraph.typing import ContextT
 
 from deerflow.agents.thread_state import ThreadState
 from deerflow.config.paths import VIRTUAL_PATH_PREFIX, get_paths
+from deerflow.utils.runtime import get_thread_id
 
 OUTPUTS_VIRTUAL_PREFIX = f"{VIRTUAL_PATH_PREFIX}/outputs"
 
 
-def _get_thread_id(runtime: ToolRuntime[ContextT, ThreadState]) -> str | None:
-    """Resolve the current thread id from runtime context or RunnableConfig."""
-    thread_id = runtime.context.get("thread_id") if runtime.context else None
-    if thread_id:
-        return thread_id
-
-    runtime_config = getattr(runtime, "config", None) or {}
-    thread_id = runtime_config.get("configurable", {}).get("thread_id")
-    if thread_id:
-        return thread_id
-
-    try:
-        return get_config().get("configurable", {}).get("thread_id")
-    except RuntimeError:
-        return None
-
-
 def _normalize_presented_filepath(
     runtime: ToolRuntime[ContextT, ThreadState],
     filepath: str,
@@ -51,7 +34,7 @@ def _normalize_presented_filepath(
     if runtime.state is None:
         raise ValueError("Thread runtime state is not available")
 
-    thread_id = _get_thread_id(runtime)
+    thread_id = get_thread_id(runtime)
     if not thread_id:
         raise ValueError("Thread ID is not available in runtime context or runtime config")