...
Login to Pulsar and make sure your organization is fully synced at least once, including your Content Library documents
From the Settings page, toggle the development server on
If you do not see the toggle, then possibly you are running a pre-3.8 version of Pulsar, or the it is likely that your org is not setup configured correctly for development mode (for your specific username)
Note that once the development server toggle is on, it is sticky per-session. You will need to re-toggle it if you re-login or re-start the Pulsar app
HTML/JS Development REPL Flow in Pulsar
In the Pulsar app, go to Find the the specific HTML/.pulsarapp document (in your Content Library) you want to debug and download/open it
First, Pulsar will load the document/bundle that is synced from your org (the org version)
Next, Pulsar will load from your development server (http://127.0.0.1:3002); on Android this is forwarded over ADB.
NOTE that this means you can move backward and forward using the window history buttons to switch between the org and development versions (if desired)
Because Pulsar is loading your HTML/JS code from your development server on your development machine, you should now be able to use all your normal HTML/JS debugging tools on the code running locally on your development machine
If you make a change to your HTML/JS code, simply restart your development server and hit the page refresh button in Pulsar