The upgrade E2E cells are the regression proof; the unit tests keep one
invariant per behaviour: full clone stays full / partial clone keeps its own
filter (#122353), crash recognizer + single promisor-disabled retry (#124272),
heal of a depth-1 clone / of a --depth-grafted full clone (#123254, #123346).
Co-authored-by: salch-cred <salch-cred@users.noreply.github.com>