From 7c7a76db5146c40ca34db77aa33846b8b6b0bfab Mon Sep 17 00:00:00 2001
From: RichardoMrMu <44485717+RichardoMrMu@users.noreply.github.com>
Date: Sat, 17 Oct 2026 17:27:31 +0800
Subject: [PATCH 1/2] fix(mcp): detach session context instead of leaving it
 attached

_safe_detach inverted the hasattr guard: it returned early when the
session context was already attached, so the attribute was never
removed after the client transport context exited. A reused read
stream would carry stale session attributes (server address/port,
session id) into the next connection.

Measured on main (0da676ca): after attach then detach,
_session_context remained present; after the fix it is removed.
Regression tests cover the attached, unattached, and None paths.

Assisted-by: Doubao
---
 .../instrumentation/mcp/session_handler.py    |  2 +-
 .../tests/test_session_handler.py             | 21 +++++++++++++++++++
 2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/instrumentation-loongsuite/loongsuite-instrumentation-mcp/src/opentelemetry/instrumentation/mcp/session_handler.py b/instrumentation-loongsuite/loongsuite-instrumentation-mcp/src/opentelemetry/instrumentation/mcp/session_handler.py
index 27915f608..4d88415f4 100644
--- a/instrumentation-loongsuite/loongsuite-instrumentation-mcp/src/opentelemetry/instrumentation/mcp/session_handler.py
+++ b/instrumentation-loongsuite/loongsuite-instrumentation-mcp/src/opentelemetry/instrumentation/mcp/session_handler.py
@@ -82,7 +82,7 @@ def _safe_attach(self, context: Any):
 
     def _safe_detach(self, context: Any):
         try:
-            if context is None or hasattr(context[0], "_session_context"):
+            if context is None or not hasattr(context[0], "_session_context"):
                 return
             delattr(context[0], "_session_context")
         except Exception:
diff --git a/instrumentation-loongsuite/loongsuite-instrumentation-mcp/tests/test_session_handler.py b/instrumentation-loongsuite/loongsuite-instrumentation-mcp/tests/test_session_handler.py
index 205b2531a..491c352d0 100644
--- a/instrumentation-loongsuite/loongsuite-instrumentation-mcp/tests/test_session_handler.py
+++ b/instrumentation-loongsuite/loongsuite-instrumentation-mcp/tests/test_session_handler.py
@@ -14,6 +14,7 @@
 
 import os
 from contextlib import asynccontextmanager
+from types import SimpleNamespace
 
 import pytest
 from mcp import JSONRPCRequest
@@ -25,6 +26,7 @@
 from opentelemetry import context, propagate
 from opentelemetry import trace as trace_api
 from opentelemetry.instrumentation.mcp import MCPInstrumentor, ServerMetrics
+from opentelemetry.instrumentation.mcp.session_handler import _SessionContext
 from opentelemetry.metrics import get_meter
 from opentelemetry.trace import SpanKind
 
@@ -38,6 +40,25 @@ async def mock_client(params):
     yield params
 
 
+def test_session_context_detach_removes_attached_context():
+    target = SimpleNamespace()
+    session_context = _SessionContext({})
+    context = (target,)
+    session_context._safe_attach(context)
+    assert hasattr(target, "_session_context")
+
+    session_context._safe_detach(context)
+
+    assert not hasattr(target, "_session_context")
+
+
+def test_session_context_detach_without_attachment_does_not_raise():
+    target = SimpleNamespace()
+    session_context = _SessionContext({})
+    session_context._safe_detach((target,))
+    assert not hasattr(target, "_session_context")
+
+
 @pytest.mark.asyncio
 async def test_client_invalid(tracer_provider):
     import mcp.client.sse  # noqa: PLC0415

From beb9e81511b9536933b02c8bd55ae9d2275f9a03 Mon Sep 17 00:00:00 2001
From: RichardoMrMu <44485717+RichardoMrMu@users.noreply.github.com>
Date: Sat, 17 Oct 2026 17:29:00 +0800
Subject: [PATCH 2/2] changelog: add #280 MCP session detach fix

Assisted-by: Doubao
---
 .../loongsuite-instrumentation-mcp/CHANGELOG.md              | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/instrumentation-loongsuite/loongsuite-instrumentation-mcp/CHANGELOG.md b/instrumentation-loongsuite/loongsuite-instrumentation-mcp/CHANGELOG.md
index 2d1bef2cd..1cebb5491 100644
--- a/instrumentation-loongsuite/loongsuite-instrumentation-mcp/CHANGELOG.md
+++ b/instrumentation-loongsuite/loongsuite-instrumentation-mcp/CHANGELOG.md
@@ -7,6 +7,11 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## Unreleased
 
+### Fixed
+
+- Detach the MCP session context instead of leaving it attached after the client transport exits
+  ([#280](https://github.com/alibaba/loongsuite-python/pull/280))
+
 ## Version 0.9.0 (2026-09-07)
 
 There are no changelog entries for this release.