feat: add optional prompt-toolkit support to debug.py (#2461)

* feat: add optional prompt-toolkit support to debug.py

Use PromptSession.prompt_async() for arrow-key navigation and input
history when prompt-toolkit is available, falling back to plain input()
with a helpful install tip otherwise.

Made-with: Cursor

* fix: handle EOFError gracefully in debug.py

Catch EOFError alongside KeyboardInterrupt so that Ctrl-D exits
cleanly instead of printing a traceback.

Made-with: Cursor

backend/debug.py

@@ -24,6 +24,14 @@ from langgraph.runtime import Runtime
 
 from deerflow.agents import make_lead_agent
 
+try:
+    from prompt_toolkit import PromptSession
+    from prompt_toolkit.history import InMemoryHistory
+
+    _HAS_PROMPT_TOOLKIT = True
+except ImportError:
+    _HAS_PROMPT_TOOLKIT = False
+
 load_dotenv()
 
 logging.basicConfig(
@@ -58,14 +66,21 @@ async def main():
 
     agent = make_lead_agent(config)
 
+    session = PromptSession(history=InMemoryHistory()) if _HAS_PROMPT_TOOLKIT else None
+
     print("=" * 50)
     print("Lead Agent Debug Mode")
     print("Type 'quit' or 'exit' to stop")
+    if not _HAS_PROMPT_TOOLKIT:
+        print("Tip: `uv sync --group dev` to enable arrow-key & history support")
     print("=" * 50)
 
     while True:
         try:
-            user_input = input("\nYou: ").strip()
+            if session:
+                user_input = (await session.prompt_async("\nYou: ")).strip()
+            else:
+                user_input = input("\nYou: ").strip()
             if not user_input:
                 continue
             if user_input.lower() in ("quit", "exit"):
@@ -81,8 +96,8 @@ async def main():
                 last_message = result["messages"][-1]
                 print(f"\nAgent: {last_message.content}")
 
-        except KeyboardInterrupt:
+        except (KeyboardInterrupt, EOFError):
-            print("\nInterrupted. Goodbye!")
+            print("\nGoodbye!")
             break
         except Exception as e:
             print(f"\nError: {e}")

backend/pyproject.toml

@@ -20,7 +20,7 @@ dependencies = [
 ]
 
 [dependency-groups]
-dev = ["pytest>=9.0.3", "ruff>=0.14.11"]
+dev = ["prompt-toolkit>=3.0.0", "pytest>=9.0.3", "ruff>=0.14.11"]
 
 [tool.uv.workspace]
 members = ["packages/harness"]