diff --git a/docs/testing.md b/docs/testing.md
index 672475b..38d5dc2 100644
--- a/docs/testing.md
+++ b/docs/testing.md
@@ -97,4 +97,10 @@ inline password. Use `Prepare`, `Run`,
 `Collect`, `Stop`, and `Reset` in that order for a native run. The VM is the
 minimum smoke lane, so deferred native multi-session/ambiguous-session, Server
 Core, and older-build entries remain explicitly blocked until their own
-fixtures exist. Wine or a protocol stub is not treated as equivalent coverage.
+fixtures exist. During the current Windows 10 fixture check, VirtualBox Guest
+Control 7.2.16 rejected the GUI-subsystem `rvbox.exe` as a directly runnable
+guest executable; wrapping it through `cmd.exe` exited the RVBox process but
+left the Guest Control wrapper waiting. The VM was restored and left powered
+off, but native runtime coverage remains blocked until the host adapter gains a
+GUI-process completion path (or a service-driven guest runner). Wine or a
+protocol stub is not treated as equivalent coverage.