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HTML5 forbids interactive content (<button>, <a>, <input>...) as descendants of <a>. The original <a href=…><button>✓</button></a> markup triggered two concrete bugs flagged by Felix, Nora, and Leonie in PR #288 review: - Browsers inconsistently route the nested click: on some engines the stopPropagation() still bubbles, and the user navigates into the document instead of dismissing. - The senior audience (60+) tap-selects with a slight drag, and the OS treats the interaction as anchor vs. button inconsistently — a reproducible usability failure Leonie has seen in testing before. Refactor to the Option-C layout from issue #285 comment #3573: outer <li> flex container, <a> wrapping avatar + body + time, <button> as a sibling. Independent focus stops, invalid-HTML gone, no behavioural regression. A new spec locks the invariant: `dismiss.closest('a')` must be null. Part of #285, address PR #288 review. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>