diff --git a/src/sections/items.tex b/src/sections/items.tex
index 264d4fb..b5a13e9 100644
--- a/src/sections/items.tex
+++ b/src/sections/items.tex
@@ -185,6 +185,7 @@ def dummy_func(param1, param2, param4, param4):
       \item To get a variable from the global dictionnary : \incode{tm.gd("global\_dict\_key")}
       \item To set a variable from the global dictionnary : \incode{tm.setgd("global\_dict\_key", value)}
     \end{itemize}
+    \item \incode{context\_id}: share a persistent subprocess across \incode{py\_func} items
   \end{itemize}
 \end{frame}
 
@@ -205,9 +206,63 @@ end
       \item To get a variable from the global dictionnary : \incode{tm.gd("global\_dict\_key")}
       \item To set a variable from the global dictionnary : \incode{tm.setgd("global\_dict\_key", value)}
     \end{itemize}
+    \item \incode{context\_id}: share a persistent subprocess across \incode{lua\_func} items
   \end{itemize}
 \end{frame}
 
+\begin{frame}[fragile]{\incode{context\_id} — shared persistent subprocess}
+\begin{columns}
+  \column{0.5\textwidth}
+  \begin{itemize}
+    \item By default, each \incode{py\_func}/\incode{lua\_func} call spawns its own subprocess
+    \begin{itemize}
+      \item module-level state is \textbf{not} preserved between calls
+    \end{itemize}
+    \item \incode{context\_id}: items sharing the same id reuse the \textbf{same} persistent subprocess
+    \begin{itemize}
+      \item subprocess lives until the end of the test run
+      \item required for non-JSON-serializable objects (connections, handles\ldots)
+    \end{itemize}
+    \item \incode{tm.setgd}/\incode{tm.gd} always work across all items for serializable values
+    \begin{itemize}
+      \item non-serializable values (\incode{py\_func} only) are kept locally in the subprocess
+    \end{itemize}
+  \end{itemize}
+  \column{0.5\textwidth}
+    \begin{minted}[fontsize=\fontsize{6}{7}\selectfont]{yaml}
+- py_func:
+    name: open connection
+    file: my_script.py
+    func_name: open_connection
+    context_id: my_context
+    expected_result: ok
+
+- py_func:
+    name: use connection
+    file: my_script.py
+    func_name: use_connection
+    context_id: my_context
+    expected_result: open
+    \end{minted}
+    \begin{minted}[fontsize=\fontsize{6}{7}\selectfont]{yaml}
+- lua_func:
+    name: produce value
+    file: my_script.lua
+    func_name: produce
+    context_id: my_context
+    param:
+        - hello
+
+- lua_func:
+    name: consume value
+    file: my_script.lua
+    func_name: consume
+    context_id: my_context
+    expected_result: hello
+    \end{minted}
+\end{columns}
+\end{frame}
+
 \begin{frame}[fragile]{\incode{group} test item}
   \begin{itemize}
     \item \incode{steps}: The list of items in the group
diff --git a/testium_training.pdf b/testium_training.pdf
index 36dd204..5c43894 100644
Binary files a/testium_training.pdf and b/testium_training.pdf differ