Comment on: v0.4+ candidate: live-fork via memfd-backed source RAM + uffd_wp (deferred from v0.3)

**Update 2026-05-19 — narrowing scope.** v0.3 phase 1 shipped 143× on vanilla Firecracker (no fork required). The `firecracker-patch/` directory that originally drafted a `MemoryBackend::Memfd` patch has been removed (PR opened). Concretely, we're now explicitly NOT taking the memfd route, for four reasons: 1. **Phase 1 cleared ~85 % of the original target headroom** (30 ms target → 205 ms achieved on 4 GiB SSD) without any Firecracker change. 2. **memfd's value-add isn't sharing** — `mmap(MAP_PRIVATE)` of `memory.bin` across N children already gives kernel-CoW fan-out for free. memfd's real value is letting uffd_wp track source writes cleanly, but that's only useful for the live-fork architecture in `docs/design/userfaultfd.md`, which has its own deferred open questions. 3. **Fork maintenance is real cost**: own musl-via-docker CI, rebase on every upstream tag (~quarterly), track CVEs, weaken the "vanilla Firecracker" trust story users rely on. CodeSandbox went this route and hasn't...