How to reproduce:
1. Open attached project
2. In Hierarchy select Trail, make sure Trail Renderer component Mask Interaction is set to None
3. Move Trail around scene and notice orange selection outline around trails
4. Change Mask Interaction to Visible Inside Mask
5. Move Trail around scene

Expected result: selection outline is shown for selected Trail
Actual result: selection outline is not rendered, thus making it hard to see trails while outside the mask

Reproduced with: 2022.1.0a13
Mask Interaction was introduced in 2022.1.0a7

Note: Also reproduces with Line Renderer, Sprites, Particle Systems.

RichardK note: When using Visible Inside Mask, the selection outline totally vanishes. When using Visible Outside Mask, the selection outline shows up both inside and outside the mask. Presumably we need to add support to the selection shader for the visible inside/outside mask render states.