callbacks.onImageRequest

Replaces the Image tool's picker: called when the Image tool would open its file picker. Resolve with a Blob (a File is one) or null to cancel; the image is checked against tools.image like a picked file and refused with the same message. A rejection is a cancel and is logged; the SDK shows nothing for a cancel, so tell the user yourself if your flow failed. An answer that arrives after the tool was switched off is dropped.