Source content aspect ratio at authoring time.
False while the author is still mid-drag; true after pointer-up.
Globally-unique. Authored as ${authorId}:${nonce} so receivers
can attribute strokes to their author for clear-mine semantics.
Wall-clock ms; receivers GC stale in-progress strokes after a timeout to handle authors who drop mid-drag.
Wall-clock ms of the last update for in-progress GC.
Stroke width as a fraction of min(contentWidth, contentHeight) —
scales with the rendered video so a stroke drawn at a small tile
stays visually proportional when shown on a large tile.
One drawn line.
pointsare normalised against the source content's aspect ratio at the time of drawing — receivers letterbox-map the stroke into their own live content rect, so strokes stay anchored to the source no matter how the local tile is sized or whether the source resolution changes mid-share.