[tree] missing value in I/O rule for vector<T> with deep source member #19773
Description
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Description
We have a schema evolution of class T and a split branch with a vector<T>. The I/O rule for T is supposed to move a member within a struct member up to the top level. The rule runs but doesn't populate the new top-level member correctly.
Spin-off of #19650
The fix in #19688 does not work for this case. Although I assume the cause is similar: the I/O rule runs but points to the wrong staging area.
Reproducer
The following minimal example demonstrates the problem. The I/O rule is supposed to populate the new fMember with the old versions fDeep.fDeepMember. That works for all cases but split tree.
ROOT version
master
Installation method
from sources
Operating system
Linux
Additional context
No response