Implement a consistent and easy to trigger set of client-side debug flags/toggles

Problem/Motivation

It's really annoying and difficult right now to test certain things, even when running a site locally and with simulated low quality network conditions via dev tools. As an example, testing the progress bar and related behaviour that requires a significant delay between clicking a link and displaying a response is currently a pain because of the lazy link preloader being ironically very effective at already having a response instantly ready to display; you can try to scroll and click very fast to get ahead of it, but you will still fail quite often.

Steps to reproduce

See above.

Proposed resolution

Add both a cookie and a JavaScript method for triggering each; the method can set the appropriate cookie if relevant; would be good to also provide an undo method to remove the cookie.

Remaining tasks

Do the thing. The following would be quite useful:

• Disabling RefreshLess entirely for a session; see the killswitch cookie.
• Disabling Turbo caching.
• Disabling lazy link preloading.

User interface changes

None for the time being. We may provide some kind of configuration UI later on; see 📌 Turbo: Configuration and form for toggling Turbo features Active .

API changes

Additional methods and cookies.

Data model changes

None?