Computes the mirror plan from source and mirror file listings, each mapping a tree-relative path to its byte size.
Computes the mirror plan from source and mirror file listings, each mapping a tree-relative path to its byte size.
Only source files appear in the plan: a file present in the mirror but absent from the source is left in place, so custody survives vendor pruning. Size is the only signal — an Extend is a candidate the interpreter must confirm is a true prefix extension before appending.