When WP-CLI fatals on the plugin you came to rescue

A WordPress plugin update breaks the site. You SSH in to roll back the bad plugin with WP-CLI, and you get this:

Fatal error: Uncaught Error: ... in /path/to/broken-plugin/main.php:42

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The plugin you came to fix has now stopped the tool you came to fix it with. It looks contradictory, but it makes sense once you know how WP-CLI starts up — and there's a flag pair that gets you out.