fix(sandbox): guard against None runtime.context in sandbox tool helpers (#1853)

sandbox_from_runtime() and ensure_sandbox_initialized() write
sandbox_id into runtime.context after acquiring a sandbox. When
lazy_init=True and no context is supplied to the graph run,
runtime.context is None (the LangGraph default), causing a TypeError
on the assignment.

Add `if runtime.context is not None` guards at all three write sites.
Reads already had equivalent guards (e.g. `runtime.context.get(...) if
runtime.context else None`); this brings writes into line.

backend/packages/harness/deerflow/sandbox/tools.py

@@ -801,6 +801,7 @@ def sandbox_from_runtime(runtime: ToolRuntime[ContextT, ThreadState] | None = No
     if sandbox is None:
         raise SandboxNotFoundError(f"Sandbox with ID '{sandbox_id}' not found", sandbox_id=sandbox_id)
 
+    if runtime.context is not None:
         runtime.context["sandbox_id"] = sandbox_id  # Ensure sandbox_id is in context for downstream use
     return sandbox
 
@@ -836,6 +837,7 @@ def ensure_sandbox_initialized(runtime: ToolRuntime[ContextT, ThreadState] | Non
         if sandbox_id is not None:
             sandbox = get_sandbox_provider().get(sandbox_id)
             if sandbox is not None:
+                if runtime.context is not None:
                     runtime.context["sandbox_id"] = sandbox_id  # Ensure sandbox_id is in context for releasing in after_agent
                 return sandbox
             # Sandbox was released, fall through to acquire new one
@@ -858,6 +860,7 @@ def ensure_sandbox_initialized(runtime: ToolRuntime[ContextT, ThreadState] | Non
     if sandbox is None:
         raise SandboxNotFoundError("Sandbox not found after acquisition", sandbox_id=sandbox_id)
 
+    if runtime.context is not None:
         runtime.context["sandbox_id"] = sandbox_id  # Ensure sandbox_id is in context for releasing in after_agent
     return sandbox