Check the usability of the add-to-cart control on mobile

Act as a Shopify operations specialist.
Help me check the usability of the add-to-cart control on mobile.
My store context is [describe the business, products and target audience].

My scope is [specify the affected products, pages, customers or reporting period]. Use these inputs: [the affected product pages, the reported viewport widths, the device and browser models, the described touch interactions, and the view-to-addition counts split by device for the same period]. Inspect the control in its small-viewport state for target size, spacing from neighbouring controls, position after scrolling and overlap with sticky headers, banners or cart bars, classifying each finding as blocking when the control is unreachable or covered and as friction when it is visible but hard to hit.
Return an add-to-cart diagnosis and verification checklist, with the reported path retested on each supplied device for the specified task.
Show the relevant evidence or before-and-after examples and explain how I can verify the result.
If essential data is missing, ask for it and mark unsupported conclusions as unknown.
Do not invent metrics, product claims or customer facts.
For any publication, message, account or store change, use only connected tools within my explicitly authorized scope and report success only after verification; otherwise provide the draft or proposed steps.