[omartelo]

Summary

• The sidebar's resize strip moves from the gap between the sidebar and the sessions onto the sidebar's own right edge, as the Code and Review dock's sits on its left edge.
• The block list's scroll column now stops a strip's width short of the panel's edge, so its scrollbar sits left of the strip instead of under it. Cards lose 6dp.
• TestSidebarHandleSitsOnThePanelsOwnRightEdge replaces the gutter test: the contract changed. A press on the panel's edge grabs the handle; one left of the strip (the scrollbar) and one in the gap past the panel do not.

Test plan

• native/: gofmt -l ., go vet ./..., go test ./...
• go test ./internal/patchnotes/
• Rig window reviewed by the maintainer