Padding as a node, with each of the four sides its own number: a padding that
is the same all round hides anything that treats one edge differently from
another. Spans now hold two to four children, so a pattern of removals has
something to make a pattern out of.
Five ways of changing what a span holds, each a shape worth its own case
rather than one shuffle: every other child out, everything but the first out,
three on at once, the first out and three on, and one out of the middle with
one on the end. Each is applied to every third span, and the cold tree is
grown holding exactly what the warm one was left with.
Three spare leaves are grown beside every span whether they end up in it or
not, so a tree that leaves them out makes the same widgets in the same order
as one that puts them in -- otherwise the two trees' `ids` stop lining up at
the first difference and every comparison after it is against the wrong
widget. Attaching one moves it, since a widget belongs to one parent;
`upgrade` is for a weak handle that was never added, not a second share. The
detached children are held until the comparison is over for the same reason:
dropping the last share of one frees its id for the next widget to be given.
Each case asserts the tree actually changed before comparing, so a shuffle
that quietly did nothing fails rather than passes.
All of it agrees: 49 tests, and the ignored sweep over 100 seeds and eight
scenarios, 800 comparisons.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
iris-aiandClaude Opus 5
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