One stroke draws the whole thread
Every reply line is now a single continuous path on one canvas, measured from avatar to avatar. New lines that appear on screen draw themselves in over 500ms, and they stop at each ring instead of crossing the face.
Open a busy thread and follow the rail down. It runs unbroken from the first commit through every reply, around each elbow and lane change, at the same 2-pixel width. The dashes keep a 4-pixel rhythm the whole way, and the line meets each avatar's ring cleanly instead of slicing across the face. Post a reply and watch its line draw itself in over 500ms.
Credit goes to jubianchi, who replaced the hand-placed rail pieces with one canvas that measures every avatar and dot, draws each edge from centre to centre, then cuts it away at the ring. A first reply hangs off its parent on a 12-pixel rounded corner. When an edge changes lane, it holds the old color for the first half and fades into the new one.
One catch remains. The dashed rail beside the box where you post a new commit is still built the old way. It is not a node in the canvas, so it keeps its own dash and width and is not redrawn with the thread.