Complete only the hidden portion of the specified character part on the first
input image (the local canvas). Any subsequent images are context references.
Preserve the exact original pose, scale, screen direction, perspective, colors,
line thickness and shading. Do not mirror, rotate, resize, recenter or redesign.
Keep the canvas dimensions and the position of every already-visible feature.
Extend the hidden joint area naturally behind its occluder, without adding other
body parts, props, labels, annotations or extra versions of the same part.
If an edit mask is supplied, transparent mask pixels are editable. Otherwise,
use the task's bounded extension instructions and keep the remaining background
pure white or transparent. Return the same canvas size without recentering.
Downstream checks will reject misalignment, restrict additions to allowed regions,
and restore the source visible pixels. Do not rely on restoration to hide changes.
