From 1feb2ae7d541581cbc1173240cd5d4c32c9ea993 Mon Sep 17 00:00:00 2001
From: Paulo Victor Cordeiro <146781332+pvcordeiro@users.noreply.github.com>
Date: Wed, 3 Jun 2026 06:23:46 +0100
Subject: [PATCH] fix: close AsyncExitStack on MCP init/tool-discovery failure
 (#1493)
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

If session.initialize() or list_tools() raises after the stdio
subprocess or SSE connection is already open, the AsyncExitStack is
never closed — leaking the child process or HTTP connection. Wrap the
setup phase in try/except to aclose() the stack before re-raising.
---
 src/mcp_manager.py | 32 ++++++++++++++++++++------------
 1 file changed, 20 insertions(+), 12 deletions(-)

diff --git a/src/mcp_manager.py b/src/mcp_manager.py
index e588a10..811094f 100644
--- a/src/mcp_manager.py
+++ b/src/mcp_manager.py
@@ -89,14 +89,18 @@ class McpManager:
             )
 
             stack = AsyncExitStack()
-            transport = await stack.enter_async_context(stdio_client(server_params))
-            read_stream, write_stream = transport
-            session = await stack.enter_async_context(ClientSession(read_stream, write_stream))
+            try:
+                transport = await stack.enter_async_context(stdio_client(server_params))
+                read_stream, write_stream = transport
+                session = await stack.enter_async_context(ClientSession(read_stream, write_stream))
 
-            await session.initialize()
+                await session.initialize()
 
-            # Discover tools
-            tools_result = await session.list_tools()
+                # Discover tools
+                tools_result = await session.list_tools()
+            except Exception:
+                await stack.aclose()
+                raise
             tools = []
             for tool in tools_result.tools:
                 tools.append({
@@ -142,14 +146,18 @@ class McpManager:
             from contextlib import AsyncExitStack
 
             stack = AsyncExitStack()
-            transport = await stack.enter_async_context(sse_client(url))
-            read_stream, write_stream = transport
-            session = await stack.enter_async_context(ClientSession(read_stream, write_stream))
+            try:
+                transport = await stack.enter_async_context(sse_client(url))
+                read_stream, write_stream = transport
+                session = await stack.enter_async_context(ClientSession(read_stream, write_stream))
 
-            await session.initialize()
+                await session.initialize()
 
-            # Discover tools
-            tools_result = await session.list_tools()
+                # Discover tools
+                tools_result = await session.list_tools()
+            except Exception:
+                await stack.aclose()
+                raise
             tools = []
             for tool in tools_result.tools:
                 tools.append({