Add mailbox resume network handoff

[sjmiller609]

Summary

• add a guest-agent resume-network mailbox that lets the host patch the fork snapshot memory before Firecracker resume
• apply fresh MAC/IP/gateway in-process with netlink, avoiding host-initiated vsock/gRPC in reconfigure_guest_network
• add perf probes for mailbox, UDP network-ready ack, VMGenID detection, and fork resume timings

Benchmarks

Remote host: deft-kernel-dev, Firecracker, 1 vCPU, 20 forks.

• correctness: 20/20 passed with guest MAC/IP verified
• reconfigure_guest_network_ms: 0 on every iteration
• fork return time: mostly 135-193ms, range 135-331ms
• guest mailbox observed after resume_vm: ~228ms avg, range 206-317ms
• guest applied network after resume_vm: ~231ms avg, range 208-319ms
• mailbox observed to netlink applied: usually 2-3ms

Validation

• go test ./lib/system/guest_agent ./lib/guest ./lib/hypervisor/firecracker
• remote: make build-embedded
• remote: HYPEMAN_RUN_RECONFIGURE_GUEST_NETWORK_PERF=1 HYPEMAN_RECONFIGURE_GUEST_NETWORK_PERF_ITERS=20 HYPEMAN_RECONFIGURE_GUEST_NETWORK_GUEST_INITIATED=1 HYPEMAN_RECONFIGURE_GUEST_NETWORK_GUEST_PREARM=1 HYPEMAN_RECONFIGURE_GUEST_NETWORK_GUEST_MAILBOX=1 go test ./lib/instances -run TestReconfigureGuestNetworkPerf -count=1 -v

[github-actions]

✱ Stainless preview builds for hypeman

This PR will update the hypeman SDKs with the following commit message.

feat: Add mailbox resume network handoff

Edit this comment to update it. It will appear in the SDK's changelogs.

✅ hypeman-openapi studio · code · diff

Your SDK build had at least one "note" diagnostic, but this did not represent a regression.
generate ✅

✅ hypeman-go studio · code · diff

Your SDK build had at least one "note" diagnostic, but this did not represent a regression.
generate ✅ → build ✅ → lint ✅ → test ✅

go get github.com/stainless-sdks/hypeman-go@9cbf74279160585cd608cec3a69c0677027e9752

✅ hypeman-typescript studio · code · diff

Your SDK build had at least one "note" diagnostic, but this did not represent a regression.
generate ✅ → build ✅ → lint ❗ → test ✅

npm install https://pkg.stainless.com/s/hypeman-typescript/af8a47871d6ed0ce104ca886e547589057f2b12b/dist.tar.gz

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Last updated: 2026-05-30 19:11:05 UTC

[sjmiller609]

Closing in favor of #253, which combines the main ReconfigureNetwork + mailbox/VMGenID path with the exploratory pieces trimmed out. Keeping the branch for reference.