Add memory system session context API

tests/test_memory_system_server.py

@@ -4,6 +4,14 @@ def test_memory_system_server_exposes_routes():
     paths = {route.path for route in app.routes}
     assert "/memory-system/users" in paths
     assert "/memory-system/messages" in paths
+    assert "/memory-system/sessions/{session_id}/context" in paths
+    context_methods = {
+        method
+        for route in app.routes
+        if getattr(route, "path", "") == "/memory-system/sessions/{session_id}/context"
+        for method in getattr(route, "methods", set())
+    }
+    assert {"GET", "POST"} <= context_methods
     assert "/memory-system/search" in paths
     assert "/memory-system/users/{user_id}/profile" in paths