P74（启动开场过渡：水墨式渐显）证据分析 — 真实 Desktop xvfb 1280x720
钩子：LV_P74_SHOT=1（60Hz 固定步进，splash 帧表 8/30/60/100/140 各一帧）
路径：splashFrame → InkReveal.inkStrength/dabs（预乘墨滴）→ 露出天色/水面/屋脊/标题

log shots: 8(ink=0.770), 30(ink=0.325), 60(ink=0.053), 100(ink=0.000), 140(ink=0.000)

p74-splash-008.png: size=1280x720 brightness=46.5 std=25.6 dark_block=0 white_block=405
p74-splash-030.png: size=1280x720 brightness=51.7 std=38.4 dark_block=0 white_block=232
p74-splash-060.png: size=1280x720 brightness=56.0 std=48.9 dark_block=0 white_block=232
p74-splash-100.png: size=1280x720 brightness=56.4 std=49.0 dark_block=0 white_block=232
p74-splash-140.png: size=1280x720 brightness=56.4 std=49.1 dark_block=0 white_block=232

diff frame 008 vs 030: differing_pixels=670116
diff frame 008 vs 060: differing_pixels=686287
diff frame 008 vs 100: differing_pixels=528158
diff frame 008 vs 140: differing_pixels=537994
diff frame 030 vs 060: differing_pixels=733221
diff frame 030 vs 100: differing_pixels=692402
diff frame 030 vs 140: differing_pixels=702640
diff frame 060 vs 100: differing_pixels=525583
diff frame 060 vs 140: differing_pixels=545037
diff frame 100 vs 140: differing_pixels=120790

verdict=PASS
  ink strength decays to 0 across the captured frames; frames render 1280x720,
  no big black/white blocks, and every pair differs (the opening transition animates).