diff --git a/UnityMcpBridge/UnityMcpServer~/src/telemetry.py b/UnityMcpBridge/UnityMcpServer~/src/telemetry.py
index fd9e82c..bc62b95 100644
--- a/UnityMcpBridge/UnityMcpServer~/src/telemetry.py
+++ b/UnityMcpBridge/UnityMcpServer~/src/telemetry.py
@@ -192,9 +192,13 @@ class TelemetryCollector:
     def _save_milestones(self):
         """Save milestones to disk"""
         try:
-            self.config.milestones_file.write_text(json.dumps(self._milestones, indent=2))
-        except Exception as e:
-            logger.warning(f"Failed to save milestones: {e}")
+            with self._lock:
+                self.config.milestones_file.write_text(
+                    json.dumps(self._milestones, indent=2),
+                    encoding="utf-8",
+                )
+        except OSError as e:
+            logger.warning(f"Failed to save milestones: {e}", exc_info=True)
     
     def record_milestone(self, milestone: MilestoneType, data: Optional[Dict[str, Any]] = None) -> bool:
         """Record a milestone event, returns True if this is the first occurrence"""
diff --git a/tests/conftest.py b/tests/conftest.py
new file mode 100644
index 0000000..a839e9c
--- /dev/null
+++ b/tests/conftest.py
@@ -0,0 +1,8 @@
+import os
+
+# Ensure telemetry is disabled during test collection and execution to avoid
+# any background network or thread startup that could slow or block pytest.
+os.environ.setdefault("DISABLE_TELEMETRY", "true")
+os.environ.setdefault("UNITY_MCP_DISABLE_TELEMETRY", "true")
+os.environ.setdefault("MCP_DISABLE_TELEMETRY", "true")
+