Thanks for trying Spell Cascade and for reporting this bug! You're right — there was a GDScript type inference issue that caused the web build to fail loading the main game script. The title screen loaded fine, but the actual gameplay couldn't start because of the parse error you saw in the console.
I've just pushed a hotfix (v0.3.5-hotfix1) that resolves this. Could you try refreshing and playing again? You should now see enemies spawning, spells to chain, and the full gameplay loop. The R key for restart only works after a game over, so that part was actually working as intended — it just never got that far because of the script error.
Really appreciate you taking the time to check the console and report the specific error. That made it much easier to track down!