Session hands global/<n> to the redefinition when a def is re-evaluated,
and that target is not a sibling — its fparent is the global — so its cell
declaration comes from Emit.redefinition's targets pass, a path no test
compiled: the dev-rerun leg runs on x86 merged, which reaches host cells
through the GOT and never needed the declaration. reload.flan carries a
(def paint i64 7) now and test_reload greps the module text for the cell
extern and the hidden body, which is the idiom the file already uses.