scr_union_release buffered every union box left alive by a release as a
cycle-collector candidate, including boxes whose arm_trace is NULL (scalar
arms, and ref arms whose type the compiler proved acyclic, such as
TreeNode | null once TreeNode is constructor-only). Such a box's trace visits
nothing, so it can never be on a collectable cycle: skip the candidate
buffer for it. Deaths check the header's buffered bit inline before calling
scr_cyc_on_dead, because typed-ref cache commits swap arm contents between
boxes of one union type, so a box can have been buffered under an earlier
arm.
test_closure.c checks that string- and f64-armed boxes are never buffered,
that closure-armed boxes are, and that a closure -> box -> union -> closure
cycle is still collected under the RC audit.
- Preserve callback identity, receiver binding, and class references across unions and collections.
- Track record field presence independently of undefined values and improve native runtime behavior.
- Expand differential coverage and streamline CI bootstrap and compiler rebuild checks.
Malte Ubl