The ring reduction already reads its pixels four at a time; the pass that flags the strong ones
still read them one at a time, over the same image. Give it the same quad read.
The flag is a per-pixel comparison against a threshold the reduction has already fixed, so nothing
is summed here and the result is unchanged pixel for pixel, including the tail the quad read does
not cover and the masked pixels it skips.
Split out of "Find the first pass's spots on every worker" on 2608-performance, which carried it as
an unrelated rider.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011n8riB6X59oRjkrSHzNPAU
