A transition owns a window.
The transition duration defines how long both scenes participate in the handoff. Keep that window intentional so the cut supports the pace of the edit.
Move the mask, not the clock.
Drive a wipe from the current frame and interpolate its position. The result stays reproducible in the preview, render, and any agent-generated composition.
Keep both sides legible.
A transition should reveal the incoming scene while the outgoing scene still has a clear exit. Scrubbing is the fastest way to inspect the midpoint.