In sveltekit, what's the convention for splitting client side code between route files?
The question has been clearly answered in the Documentation. The separate file is for loading and constructing data that is required by your route, the script tag is for DOM manipulation and client side logic.
That is the convention as per the docs but you are free to use both methods as per your preference but +page.server.js/ts is strictly  for server side logic like authentication and database calls.

Both +page.js/ts and the <script><script/> tags within +page.svelte files are for processing client side code.
What's the typical convention for choosing between these 2 files?
