Light trails, sliced in: a bar reveal from the raw rainy street into my highlight-trail version (Bar reveal). Starting footage: the same 10 s vertical rainy-street clip as my first entry, plus the Highlight Trail shader stack the agent built for it. What I asked the timeline agent: in the half second before the cut, the trail version should appear over the raw street as five thin floating vertical bars, inset top and bottom, popping in left to right with a short white flash each, then a hard cut to the full trail shot. Nothing generated. What the agent did: the Crop effect had no writable controls, so it wrote its own bar_reveal shader with controls for bar count, width, inset, stagger and flash, built a separate 9:16 timeline and checked frames at 3.6, 3.8, 3.95 and 4.2 s. What I refined: pass 1 bars looked milky, so I asked for full-contrast interiors, wider bars (0.075 to 0.10) and a slower stagger (6 to 8 frames). Pass 2 fixed the contrast but turned the street around the bars black. Pass 3 flipped the mask so the raw street keeps playing around the bars and the trails show inside. The walkthrough was assembled by the same agent in invideo Editor. invideo Editor is free to try.