Graph Toolkit visualization API silently stops affecting the graph canvas after the graph window is closed and reopened

Steps to reproduce:

1. Open the attached "ReproProject" project
2. Open the Stale Session Repro window (Window > Graph Toolkit > Stale Session Repro)
3. Click "1 · Create the repro graph and open it"
4. Click "2 · Apply visualization"
5. Observe the graph window: the transition is drawn red, dashed and thick, and the left state has an accent bar
6. Close the "StaleSessionRepro" graph window
7. In the Project window, double-click "Assets/GtkTransitionRepro/StaleSessionRepro.gtkrepro" to reopen it
8. Observe the transition and the left state in the reopened graph window

Actual results: After reopening, the canvas is drawn with the default appearance and no customization is ever applied to it again. Re-applying through the same Context changes nothing

Expected results: The stored customization is re-applied to the reopened canvas

Reproducible with versions: 6000.7.0b1

Can’t test with versions: 6000.0.0f1, 6000.0.84f1, 6000.3.24f1, 6000.6.2f1 (due to the feature not existing)

Tested on (OS): MacOS Silicon Tahoe 26.6.2, Ubuntu 24.04