Content-hash key into GigaDocument.resources.images.
A decimal string: the underlying id is a full 64-bit hash, which does not
survive JSON.parse as a JavaScript number (precision is lost past 2^53,
silently orphaning the reference from its resource — every image was
dropped from toModel() → modelTo* round-trips). The engine emits it as
a string and accepts either form (string canonically, legacy number
for hand-built models with small ids).
Optionalsize_Authored display size [width, height] in points (DOCX inline
wp:extent) — a flow image re-exports at its real size instead of a
default extent. Omitted when the source carried none. Present since 0.117.0.
OptionalcropSource-rectangle crop [left, top, right, bottom] inset fractions
(0..=1 each; DrawingML a:srcRect). Omitted = uncropped. Present
since 0.117.0.
A reference to an image blob in the document's resource table (
model::ImageRef).