RFC 019 lands upstream: per-actor stacks, park-path shrink, recycle zap,
SIGSEGV diagnostics, introspect surface. No urus code changes required —
E1 interleaved A/B on the box shows every ka cell within +0.3..+2.9% of
the v0.5.0 pin (t8-c4 close-mode control is bistable either side; see
smarm v0.6.0 release notes). Tag must exist upstream before this builds:
push smarm master + v0.6.0 first.
