I'm new to IDEA and gradle, but my understanding is that

build.gradle

specifies dependencies, which gradle constructs its build model from. My sense, and I could be wrong, is that such dependencies should be captured only in this file, and will therefore be available both at the command-line and within IDEA (or any other IDE that supports gradle). Currently, the dependency (on plugin-interface) is in 3 places: 1)

testImplementation

in gradle, for testing only 2) in the command

java -classpath "./core/*:./plugin-interface/*" io.supertokens.Main ./ DEV

, only when

./startTestingEnv --wait

is running and with @User's suggestion, now: 3) IDEA Module settings