How would you solve stop word detection in stream?

I recently failed on this interview question:

Part 1:

Given a string and a list of stopwords, return the substring that appears before the first occurrence of any stopword.

Part 2:

What if the input is a stream and cannot be fully loaded into memory?

Example:
stopWords = ["<end>", "<stop>", "/n"]
stream = Iterable(["Hello ", "world<st", "op>Welcome back"])

Expected output:
Iterable(["Assume ", "the world is great"])

I managed part 1 but couldn't get a solid solution for part 2. Tried a sliding buffer approach where I only have the maxStopWord length in memory, but I couldn't get the output chunks match the example.