Describe a chart people can act on

Given [CHART DESCRIPTION], [DATA TABLE] and [PAGE PURPOSE], write accessible chart support in three layers: a one-sentence alt text, a longer nearby description with key trend and exceptions, and keyboard instructions for any interactive controls. Preserve exact units, date range and denominator. If the data table is unavailable, do not invent values; list what must be supplied. Return the three layers plus a test checklist for screen reader, keyboard and zoom. Avoid using colour as the only cue and do not announce decorative grid lines or every individual point unless the user needs them.