The Echo-Riddle of Corvenne Sinkhole

At the bottom of Corvenne Sinkhole lives a spirit that answers every number shouted down to it with a number of its own. The Lanternwright Expedition has worked out its rule. The spirit takes the number it heard, squares each of its decimal digits, and echoes back the sum of those squares. The expedition then shouts that echo down again, and so on. Sooner or later the spirit says a number that has already been spoken in the chain. The expedition's scribes want the whole chain recorded up to that moment.

Write echoChain(seed).

• seed is a positive integer (at least 1): the first number shouted into the sinkhole.
• The next value after a number v is the sum of the squares of the base-10 digits of v. For example, 130 becomes 1 + 9 + 0 = 10.
• Return a list of integers. It starts with seed, followed by each successive value in order.
• Stop just before the first value that already appears in the list, so every value in the returned list is distinct.
• The repeated value may be any earlier entry, not necessarily seed. It is not included a second time.