Parent: #267\nDepends on: #262\nRoadmap: #142, #134\n\nPin the selected finished Wasm GC proposal and implement its type-system and validation surface.\n\nAcceptance:\n- [x] Check in exact revision, dependency, opcode/type, file, and command inventories with no implicit proposal drift.\n- [x] Decode recursive/subtype groups, heap/reference types, structs, arrays, casts/tests, and related instructions behind the GC gate.\n- [x] Validate canonical type identity, subtyping, nullability, field mutability, packed storage, instruction stacks, and disabled features exactly.\n- [x] Add malformed/invalid, recursion-depth, allocation-failure, and deterministic-diagnostic witnesses plus drift verification.
Parent: #267\nDepends on: #262\nRoadmap: #142, #134\n\nPin the selected finished Wasm GC proposal and implement its type-system and validation surface.\n\nAcceptance:\n- [x] Check in exact revision, dependency, opcode/type, file, and command inventories with no implicit proposal drift.\n- [x] Decode recursive/subtype groups, heap/reference types, structs, arrays, casts/tests, and related instructions behind the GC gate.\n- [x] Validate canonical type identity, subtyping, nullability, field mutability, packed storage, instruction stacks, and disabled features exactly.\n- [x] Add malformed/invalid, recursion-depth, allocation-failure, and deterministic-diagnostic witnesses plus drift verification.