fix: pin metamorph nix cargo hash

feat: surface frontier coverage through search progress

feat: add frontier ledger sector stats

feat: prove cross-surface sector reuse

feat: share sector preparation across runtimes

chore: close breadcrumb resume voyage

feat: resume interrupted sector rebuilds

feat: persist breadcrumb journals during rebuilds

feat: load clean sectors for direct search

feat: add sector cache model substrate

plan: activate sector cache reuse execution mission

docs: complete sector frontier cache mission

chore: review sector frontier cache mission

feat: add incremental indexing progress and reuse

chore: verify model preparation mission