Keep node cards and connection lines on the same compositing path

[dovvnloading]

Problem

While dragging a node, its connection line can visibly trail or stutter instead of staying pinned to the node. The problem was reported as dark-mode-only: switching the app to the light theme makes it disappear.

The two behaviors have one explanation. Node cards are moved by the graphics processor as independent layers - the browser quietly promotes them to that fast path once their position starts changing every frame. The connection lines live in a drawing layer that is redrawn on the main processor. Content traveling by two different routes to the screen can arrive a frame out of step, and when it does, the line lags the node it is attached to. A thin bright line on a near-black background makes each misstep obvious; the identical misstep on a white background is nearly invisible. Dark mode does not cause the problem - it reveals it. This is also why measurements of the page's internal layout kept reporting the line perfectly attached while the screen showed otherwise: the divergence happens after layout, at the final composition step.

Change

One stylesheet addition: declare will-change: transform on both the node wrappers and the connection layer. This tells the browser up front to give both the same treatment, instead of promoting nodes to a separate path partway through a drag gesture. No behavior, markup, or code-path changes - the drawing pipeline is simply aligned from the first frame.

Test plan

• Production build succeeds with the change
• Verify in the desktop app, dark theme: drag a connected node slowly around the canvas and confirm the connection stays pinned to the node - this is the reporter's reproduction and requires visual confirmation on the affected machine