In your list of examples, you have this piece of code:

let old = Array("abcd")
let new = Array("adbc")
let changes = diff(old: old, new: new)

// Move "d" from index 3 to index 1

Is this indeed correct or was this before introducing the Heckel algorithm?

Haven't verified this, but doesn't Heckel produce all three moves in this case? I.e.:

// Move "d" from i

The current code doesn't handle the case that a change in the feed runs off the end of a chunk from the http request. In this case, one or more additional chunks are required to complete the change. As-is, the attempt to parse the partial JSON fails.