runId immediately. Poll Get a tool run until it completes.
A media input is {"assetId": "..."}, an asset in the workspace (see Upload an asset), or {"url": "https://..."}. A source url must be a tool input of the workspace (see Upload tool inputs); anything else returns 400 with code set to input_not_in_workspace. A few tools still need an assetId source. Every other input is its plain value.
The same daily spend cap, concurrency limit and rate limit as Start a generation apply. Needs the tools:run scope.