Sometimes Astro slots fail to render/hydrate

Overview

On a Zoom with @lauriii, he showed me how several times a page with many code component instances would occasionally show up in the canvas with blank space showing up where code component instances should be. There were no errors in the console log. Viewing the srcDoc of the iframe showed all the Astro islands there as expected, but inspecting the DOM showed that slots in some Astro islands weren't hydrated.

According to @lauriii, he's run into this frequently enough for it to be annoying, but he hasn't found reliable steps to reproduce it.

Proposed resolution

User interface changes