P1. The project reads only `export/` -- the manifest, a screen's JSON and its
PNGs -- and draws every element at `rest`, in the export's own `paint_order`.
Three choices worth the words:
* `ExportTree` addresses screens by manifest NAME, never by path, and checks
`format` on the manifest and on each screen before drawing. Textures are
decoded from bytes at runtime rather than Godot-imported: `export/` is
gitignored and regenerated wholesale, and a `.import` per sprite would be
derived state next to derived state, invalidated on every re-export.
* One CanvasItem draws the whole screen. `paint_order` is already back-to-front,
so honouring it is a loop; spreading it across sixteen nodes' z-indices would
hide the one unresolved thing about that order -- the ties -- behind Godot's
sibling rules.
* The screen renders into a SubViewport sized to the export's `design` rect.
Capturing the window instead gave 1280x720 of screen minus a window manager's
title bar: 1235x695. A gate that rescales that to compare against a 1280x720
composite is measuring the compositor.
Nearest-neighbour filtering, because the export is a 1:1 copy of the disc's
texels, elements draw at up to 500 %, and it is what `ui_layout::blit` does --
so a filter difference cannot masquerade as a placement difference in the diff.
No keyframe interpolation and no focus state: both depend on constants that are
MEASURED rather than decoded (HANDOFF Q1, Q5), and a pixel-diff gate must not
have one of those inside it. P2 and P5.
