Make a dense data table useful on a small screen

Given [TABLE COLUMNS], [PRIMARY USER TASK] and [SCREEN WIDTH], propose a responsive design that keeps row identity, sorting and comparisons intact. Identify columns that may collapse into details, fields that must remain adjacent and a text export format. Specify keyboard focus, sticky-header behaviour and how filters announce their effect. Do not silently hide critical values or replace exact numbers with ambiguous icons. Provide a paper wireframe description and five acceptance tests. Check that a user can still compare two rows and recover the original full data.