Two Lists, One Clear Line-by-Line Difference

Goal Build a tiny offline viewer that compares two short lists of text lines and makes their differences easy to inspect. Deliverable One self-contained UTF-8 HTML file with any descriptive .html filename, at most 25,000 bytes. It must open locally without a server or internet. Requirements 1. Provide labelled Left and Right multiline text inputs and a keyboard-operable Compare button. Compare only when that button is activated. 2. Treat lines as case-sensitive strings. Normalize CRLF and CR to LF, trim leading and trailing whitespace on each line, discard blank lines, and remove duplicate lines while preserving first occurrence. 3. Display three labelled results with counts: Only Left, Both, and Only Right. Preserve Left order for Only Left and Both, and Right order for Only Right. Show an explicit empty-state message for empty results. 4. Limit each input to 100 nonblank lines before deduplication and 10,000 characters before normalization. If either limit is exceeded, show which input failed and clear prior results. 5. Include a visible sample with Left lines apple, pear, apple and Right lines pear, plum. Its expected results are Only Left: apple; Both: pear; Only Right: plum. Empty inputs must produce three empty results. Apple and apple must remain distinct. 6. Render input as plain text, never HTML. Strings such as <b>apple</b> must remain literal text. Use no eval or dynamic code generation. 7. Use native controls, visible keyboard focus, readable contrast, a polite live status announcement, and a layout that works at 360 and 1200 CSS pixels. Negative scope No file upload, download, clipboard access, storage, network requests, external assets or libraries, fuzzy matching, sorting controls, accounts, tracking, or extra files. Pass/fail acceptance gates - One offline HTML within the file limit and with all three result groups. - Correct normalization, duplicate handling, ordering, case sensitivity, empty states, and sample results. - Correct input limits, stale-result clearing on error, literal text rendering, and required accessibility features. - No prohibited features or unsafe code. Scoring rubric (100 points, in order) 1. Comparison correctness and edge-case handling: 50 points. 2. Clear results and scope compliance: 20 points. 3. Accessibility and useful validation messages: 20 points. 4. Readable code and visual polish: 10 points. Tie-breaker Prefer the implementation whose comparison and literal-text rendering are easiest to verify from readable code, then the clearest results. Styling is open. Review uses this public brief, including additional examples of these same stated rules, and no hidden features or filename requirements. One best valid submission receives the posted bounty after expiry, subject to marketplace fees.