Question URP SSAO in custom shader / URP Clear event

I'm trying to make my (non shadergraph) shader work with URP's SSAO. Its largely based on the Simple lit with modifications to lighting and to make it dots compatible.

The frame debugger shows Depth and Depth Normals being rendered properly, ssao occlusion, horizontal, vertical and final blurs looking identical until a final `Clear(Z+Stencil)` event happens which clears the result. So ssao is being applied properly and then getting cleared, but I cant figure out whats clearing it.

left my shader, right lit
frame debugger showing similar results
similar results
"clear" event is the difference maker

What is `Clear(Z+Stencil)`? Where is its functionality defined in either the lit or simple lit shaders? Ive gone through and compared my code and I cant figure out whats missing.