S-143608: Add Clean Choice, a Chromium extension that equalizes lopsided upsell choices

README.md

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 Welcome to String's open source utilities repository! This is a collection of scripts, gists, and tools that we reference in our content and share with the community.
 
 This project is licensed under the MIT License - see the [LICENSE](LICENSE) file for details.
+
+## Contents
+
+- [`clean-choice/`](clean-choice/) — a Chromium extension that spots checkout upsells where the way to decline is visually suppressed and, on request, shows both choices as equal buttons.

clean-choice/.gitignore

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+node_modules/

clean-choice/README.md

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+# Clean Choice
+
+A Chromium extension that finds checkout upsells where the way to decline is visually suppressed —
+a big "Upgrade" button next to small, grey, underlined "Continue" text — and, when you ask, shows
+both choices as equal buttons.
+
+It only acts when you click it. It reads visible buttons, their names and their computed styles on
+the current tab. It never reads what you typed into a form, never sends anything off the machine,
+never chooses for you, and never invents a price.
+
+## Install
+
+1. Open `chrome://extensions` and switch on **Developer mode**.
+2. Click **Load unpacked** and pick `clean-choice/extension`.
+3. Pin **Clean Choice** to the toolbar.
+
+On a checkout page, click the toolbar icon, then **Scan page**. Each upsell/decline pair is listed
+with the evidence behind its verdict. **Show on page** outlines the two original controls; **Show
+both equally** replaces them with two same-size buttons; **Undo** puts the page back. **Off for
+this site** stops the extension on that origin and undoes anything it changed there.
+
+## How it decides
+
+A pair is an offer control (upgrade, add, protect, premium, a price…) and a decline control
+(continue, no thanks, skip, without…) within four levels of a shared container or the same form or
+dialog. Back, Cancel, Close, "Add to cart" and "Continue shopping" are never paired, so ordinary
+primary/secondary buttons are ignored.
+
+A pair is flagged as lopsided when at least two of these hold: the offer is filled and the decline
+is not; the decline is underlined like a link; the offer is at least 3× larger; the offer's text is
+at least 1.25× larger or 200 weight units bolder; the decline's text contrast is below 4.5:1 or
+half the offer's; the decline cannot be reached with Tab. Fewer than two is reported as balanced
+and left alone.
+
+The replacement buttons call the original elements' own `click()`, so the site's handlers, form
+state and navigation stay in charge. The originals are hidden, not removed. If the site re-renders
+the controls, the panel follows the new ones; if they disappear, the panel removes itself.
+
+A price is shown only when exactly one amount appears on the offer or in the container around it.
+
+## Limitations
+
+- English wording only. Controls inside iframes or shadow DOM are not scanned.
+- Built from an airline checkout layout, reproduced in `fixtures/asymmetric.html`. It has not been
+  checked against a live checkout, which needs a real booking.
+- The tests load the real extension and exercise the page logic in Chromium, but the popup → tab
+  step needs a real toolbar click (`activeTab`), so that wiring is checked by hand.
+
+## Tests
+
+```bash
+bun install
+bun test tests/
+```
+
+The tests launch Playwright's Chromium (`bunx playwright-core install chromium` if it is missing).