The metatype type-construction builtins now run natively on the flat-memory
VM, so the construction examples run HANDLED end-to-end (no call_builtin
fallback to the legacy interp).
- Tagged-union enum_init WITH payload: allocate zeroed, write the tag at
offset 0, copy the payload at tag_size ({ header, [N x i8] } layout).
- New .call_builtin exec arm -> callBuiltinVm (VM-native mirror of the legacy
execBuiltinInner): declare(name) mints an empty forward nominal slot (shared
declareNominal, also used by declare_type); define(handle, info) reads the
TypeInfo tagged-union VALUE from flat memory and mints via defineFromInfo,
a faithful port of legacy defineEnum/defineStruct/defineTuple (all-void enum
-> real .enum per issue 0142, dup-name rejection, updatePreservingKey vs
replaceKeyedInfo). Unmodeled builtins bail -> legacy fallback (dual-path).
- Refactored the []{name,ty} decode out of registerTypeVm into a shared
decodeMemberSlice (+ decodeTypeSlice for bare-Type tuple elements).
- Correctness guard: enum_init/define assume a tag-headed layout, wrong for a
backing_type tagged union (laid out as the backing struct) — both now bail
loudly on backing_type != null rather than silent-clobber.
Examples 0614/0620/0621/0624/0632 run fully HANDLED on the VM; 0622/0623 run
define HANDLED then fall back at the still-unported type_info. VM output
byte-matches legacy for all 7. 697/0 both gates + all unit tests (added:
tagged-union enum_init payload layout).
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