A turn routed to a model that takes pixels directly sends `content` as a
parts list, and the session store deliberately ignores a plain-string
persist override for a list payload — a text override must not erase a
turn's image summary. So the override was dropped for every user on a
vision-capable main model, and the durable row kept only the caption plus a
literal `[Image attached at: ...]` / `[screenshot]`, which the renderer
cannot turn back into an image. Only vision-preprocessed (text-mode) turns
were actually fixed.
Mirror the shape instead: swap the text part for the `@image:` ref form and
keep the image parts, so the model still has the pixels for the rest of the
session, and drop the `[screenshot]` stand-in on the way into the bubble
when a ref was lifted from the same message.