Document successful HDMI hardware validation for 0.2.1

docs/troubleshooting.md

@@ -100,6 +100,15 @@ hook manually as documented in README.
 
 ## Hardware acceptance
 
+The operator confirmed successful physical HDMI input switching and recovery
+with version 0.2.1 on 2026-09-23. The tested setup and the scope of that result
+are recorded in [hardware validation](hardware-validation.md).
+
 After installation, check a normal input change, a rapid away/back change and a
 logout/login cycle. Before Hyprland login there must be no chvt invocation from
 this service. Automated tests use mocks and do not replace this hardware check.
+
+For a first normal input-switch test with the default timing, stay on the other
+input for about 40 seconds before returning. This allows the initial attempt
+and its 30-second cooldown to finish. Then test rapid switching separately;
+returns inside the cooldown can still be suppressed.