Check a project's source renditions before starting an export.

Always reports all four resolutions — 480p, 720p, 1080p and 4k — so the id is the only thing to pass. Each says whether every asset already has the rendition the render would read (has_all_renditions), which assets still need one generated (state needs_rendition or generating, with the suggested_min_dimension to downscale to), and whether the render would pull a 2K-or-larger input (uses_2k_input) — the thing that makes an export slow even when nothing is missing.

Nothing is queued: an asset reported as needs_rendition stays that way until a downscale is asked for. An export started regardless still renders — source_limited assets are upscaled, and missing ones are left out of the playlist entirely, so their clips come out empty.