In `call_closure_reuse`, the success path used a bare `pop vm` that relied on
OP_RETURN having left the stack at exactly `saved_sp + 1`. When the callee
returns a closure (or hits the bytecode-exhausted fallback path), `vm.sp` can
end up inconsistent with the parent frame's expected layout, corrupting
intermediate values such as parser combinator state in `parse-bind`/`many`/
`seq`.
Fix: read the result at the expected slot, then explicitly reset
`vm.sp <- saved_sp` before returning so the parent frame sees a clean stack
regardless of what the callee left behind.
OCaml run_tests baseline: 4525/5864 unchanged. WASM kernel tests: 24/29
unchanged. No regressions.
giles
882a4b76cb