A nested designation whose temporary is still read elsewhere is retried with
that variable demoted to a designator leaf. The check that the first tuple
element must be assigned ran before that retry, and every leaf of a wrongly
nested first element precedes the assigned ones, so the pattern looked like it
started mid-way and was rejected before the retry could restore it. The flat
deconstruction was lost for a shape that has one.
Assisted-by: Claude:claude-opus-5[1m]:Claude Code
Siegfried Pammer