image_generate and video_generate forwarded model-supplied local paths to
provider plugins, which read them off the HOST filesystem regardless of
terminal backend — inconsistent with the confinement boundary vision/video
analysis enforce (GHSA-gpxw-6wxv-w3qq), and broken for sandbox-only files.
New dispatch-layer chokepoint (_confine_source_images): under a non-local
backend, path-like image_url / reference_image_urls resolve through
tools.image_source (media-cache host reads, bounded in-sandbox exec-read,
lazy env bring-up, credential guard, 50MB cap) and reach every provider as
data: URLs — which all backends already accept. URLs/data: pass through;
local backend is a no-op. xai_video_edit/extend already require public
HTTPS URLs, so no change needed there.
Teknium