An ordinary Session's composer now uploads each image draft through the
background upload queue as soon as it is added. The raw upload route stages
the body as a prompt image when the request names its media type: the Host
reads at most the per-image byte limit, then validates, normalizes, and
stores the image as prompt admission would. The prompt cites the receipt in
a file part; prompt admission resolves it to the stored image, applies the
image-input check, and counts stored images toward maxImagesPerMessage.
Send waits for every image receipt, and a failed image upload turns its
thumbnail into a retry control. Commands and subagent continuations keep
encoding images inline.