Combine and reconfirm captured original MR commit context #634

Combine existing strict MR identity, advertised membership, fixed target commit detail and literal original diff readers through one captured account client. Reconfirm MR origin metadata and selected membership after traversal; reject missing membership or contradictory reported parents, while preserving unknown source/parents and literal omission metadata. Guard every await and discard obsolete outcomes.

Test first against real injected API adapters, including forks, changed origins, traversal, late failures and no writes/fallback reads. This read aggregate does not choose original refs/coordinates or make private writes safe; guarded literal selection/controller/UI remains next. Related to MW-07, #630 and #632.