fix: make AgentGraph destructor loop-safe to prevent connection leaks

[bhavyakeerthi3]

Problem

The AgentGraph destructor (__del__) currently calls asyncio.run(self.close_pool()). In an asynchronous environment (like a Chainlit or FastAPI server), if the agent instance is deleted while an event loop is already running, asyncio.run() raises a RuntimeError: This event loop is already running. Because the destructor fails mid-execution, the connection pool is never closed, leading to hanging database connections and potential pool exhaustion.

Fix #146

Updated the destructor to be loop-aware. It now checks for a running event loop and schedules the cleanup task using loop.create_task() instead of attempting to start a new nested loop.

Important

loop.create_task() during __del__ is best-effort. If the event
loop closes before the task executes, cleanup may still be skipped.
The robust long-term solution is explicit lifecycle management via a
shutdown() method, but this fix resolves the immediate
RuntimeError and improves reliability during server reloads.

Verification

Verified with a standalone validation script covering two scenarios:

1. Active Loop: Confirmed that close_pool is scheduled as a task when a loop is running.
2. No Loop: Confirmed that asyncio.run is used as a fallback when no loop is present (e.g., script exit).

Files Affected

• src/agent/graph.py