feat(github-mark-viewed): add userscript to toggle PR file "Viewed" with "v"

Mirrors the GitLab equivalent for GitHub PR "Files changed" pages, picking
the file closest to the top of the viewport when many files are open.

Author: solcik

README.md

@@ -13,6 +13,7 @@ the `==UserScript==` header and prompts to install.
 | Script                       | Install                                                                                         | Description                                                                                                               |
 | ---------------------------- | ----------------------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------- |
 | `gitlab-mark-viewed.user.js` | [install](https://raw.githubusercontent.com/solcik/userscripts/main/gitlab-mark-viewed.user.js) | Press `v` on a GitLab MR diff to toggle the focused file's "Viewed" checkbox. Matches `gitlab.com` and `git.vs-point.cz`. |
+| `github-mark-viewed.user.js` | [install](https://raw.githubusercontent.com/solcik/userscripts/main/github-mark-viewed.user.js) | Press `v` on a GitHub PR "Files changed" page to toggle the focused file's "Viewed" button.                               |
 
 ## Authoring
 

github-mark-viewed.user.js

@@ -0,0 +1,60 @@
+// ==UserScript==
+// @name         GitHub — mark file as Viewed with "v"
+// @namespace    https://github.com/solcik/userscripts
+// @version      0.1.0
+// @description  In a GitHub pull request "Files changed" view, press "v" to toggle the focused file's "Viewed" button.
+// @author       David Solc
+// @match        https://github.com/*/*/pull/*/files*
+// @icon         https://www.google.com/s2/favicons?sz=64&domain=github.com
+// @homepageURL  https://github.com/solcik/userscripts
+// @supportURL   https://github.com/solcik/userscripts/issues
+// @updateURL    https://raw.githubusercontent.com/solcik/userscripts/main/github-mark-viewed.user.js
+// @downloadURL  https://raw.githubusercontent.com/solcik/userscripts/main/github-mark-viewed.user.js
+// @require      https://cdn.jsdelivr.net/npm/mousetrap@1.6.5/mousetrap.min.js
+// @grant        none
+// @license      MIT
+// ==/UserScript==
+
+(function () {
+  'use strict';
+
+  // Pick the "Mark as Viewed" button whose file is closest to the top of the viewport.
+  function findFocusedViewedButton() {
+    const buttons = document.querySelectorAll('button[class*="MarkAsViewedButton-module"]');
+    if (!buttons.length) return null;
+
+    const focusLine = window.innerHeight * 0.25;
+    let best = null;
+    let bestDist = Infinity;
+
+    for (const btn of buttons) {
+      const file =
+        btn.closest('[data-testid="diff-file"]') ||
+        btn.closest('copilot-diff-entry') ||
+        btn.closest('.file') ||
+        btn.closest('[id^="diff-"]') ||
+        btn.parentElement;
+      if (!file) continue;
+
+      const rect = file.getBoundingClientRect();
+      if (rect.bottom < 0 || rect.top > window.innerHeight) continue;
+
+      const dist =
+        rect.top <= focusLine && rect.bottom >= focusLine
+          ? 0
+          : Math.min(Math.abs(rect.top - focusLine), Math.abs(rect.bottom - focusLine));
+
+      if (dist < bestDist) {
+        bestDist = dist;
+        best = btn;
+      }
+    }
+
+    return best;
+  }
+
+  Mousetrap.bind('v', function () {
+    const btn = findFocusedViewedButton();
+    if (btn) btn.click();
+  });
+})();