docs: add direct session validation runbook

README.md

@@ -22,3 +22,26 @@ cargo run -p ferese -- foot
 ```
 
 Set `RUST_LOG=ferese=debug` for detailed compositor logging.
+
+### Direct DRM session
+
+Run the hardware backend from a spare TTY, outside another graphical session:
+
+```bash
+RUST_LOG=ferese=debug cargo run -p ferese -- --backend=drm -- foot
+```
+
+Do not run that command from a terminal inside the active desktop: the direct
+backend requests control of the seat and primary DRM device. Use
+Ctrl+Alt+F1–F12 to switch virtual terminals.
+
+M4 validation requires the direct session to:
+
+- start `foot` and render the same animated tiling workload as the nested path;
+- retain keyboard and pointer input;
+- pause when switching away and redraw after switching back; and
+- log page-flip timing and any missed presentation deadlines on the reference
+  integrated GPU.
+
+The direct path currently targets one connected output. Multi-output hotplug is
+part of M5.