Add mailbox resume network handoff

[sjmiller609]

Summary

• add guest-agent ReconfigureNetwork RPC backed by in-process netlink, with host fallback to the existing shell reconfigure path for older guests
• add a VMGenID-triggered resume-network mailbox so fork restores can patch guest network config before resume and avoid host-initiated guest contact on the fast path
• re-include the public wait_for_network option for running fork results; it defaults to true and waits for a guest UDP applied ack, while false returns after resume with mailbox reconfigure continuing asynchronously
• document the runtime handoff behavior in lib/forkvm/README.md
• keep the change focused by omitting the arm RPC, polling/fetch server, vsock timing instrumentation, and perf harness from the earlier exploratory PRs

Tests

• go test ./lib/guest ./lib/system/guest_agent -count=1
• go test ./lib/oapi -count=1
• go test ./cmd/api/api -run 'TestForkInstance_Success|TestForkSnapshotMapsWaitForNetwork' -count=1 (fails in this checkout because embedded hypervisor, guest-agent, and caddy binaries are missing)
• go test ./lib/instances -run 'TestGuestNetworkReconfigureConfig|TestGuestNetworkReconfigureCommand|TestPatchGuestResumeNetworkMailbox' -count=1 (fails in this checkout because embedded hypervisor and guest-agent binaries are missing)

[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@6a96a4b9dce869d0815cc4f5194e067c06f706fe

✅ 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/f97c4cbabc16367b4f7f512014fcd965c0aeb7b3/dist.tar.gz

---

This comment is auto-generated by GitHub Actions and is automatically kept up to date as you push.
If you push custom code to the preview branch, re-run this workflow to update the comment.
Last updated: 2026-05-30 19:44:33 UTC