What are the advantages of using Set here?

In the next lines, I iterate through message store threads only once and if the condition is met I add value to the array, which means each value will occur only once

right, good catch

this comment was a note I made while developing and forgot to remove, I will simply get rid of this comment

Lets assume that:
A - old state
B - state modified in reducer, the current logic
C - state modified by ops

previously it worked like this:

1. We have an old state (l A)
2. We modify the state (A -> B)
3. We return the modified state (B)

this diff this changes to:

1. We have an old state (A)
2. We modify the state and generate ops (A ->B)
3. We take the old state, apply ops, and check if this matches the modified state (A -> C, and then checking B === C)
4. We return modified state (B)

In future, if devs will not encounter any issues:

1. We have old state (A)
2. We will remove modifying the state and only generate ops (A not changed)
3. Apply ops to old state (A -> C)
4. Return state modified by ops (C)

in this function as threads we return filteredThreads which are threads from the message store whose ids are "watched".

1. We can either take the diff of reassignedMessageStore.threads and filteredThreads and remove those
2. Use threadsToRemoveMessagesFrom which is created in a loop that iterates through all reassignedMessageStore.threads (see line 667) and select those which are not present in watchedThreadInfos (current solution and better in terms of perf I think)