A base merge whose only product-side change is a registered output the
pregate regen check proved fresh now carries the receipt. A rebased head
carries when its tree is one the receipt covers and its product patch-id
against the current base matches (RECEIPT_CARRY_TREE_MISMATCH otherwise).
Docs: merge main into a reviewed branch, never rebase it.
Co-authored-by: capy-ai[bot] <230910855+capy-ai[bot]@users.noreply.github.com>