revert: remove in-VM erofs creation, use host-side umoci extraction

[hiroTamada]

Summary

This reverts commit 8f3e617.

The in-VM erofs creation optimization had issues with OCI edge cases that go-containerregistry/umoci handles correctly:

• Directory symlinks (/bin -> usr/bin) not working through overlay+erofs
• Manual tar extraction missing edge cases in whiteout handling

The optimization saved ~30% build time but caused fork/exec /bin/sh: no such file or directory errors for images using merged /usr directories (common in modern Debian/Ubuntu-based images like Python).

Root Cause

The manual tar extraction + custom whiteout processing in createErofsFromRegistry doesn't handle all OCI edge cases. Specifically, when /bin is a symlink to usr/bin (standard in Debian 12+, Ubuntu 20.04+), the overlay+erofs combination fails to resolve /bin/sh correctly at runtime.

Solution

Revert to the slower but correct host-side extraction pipeline (umoci + mkfs.erofs) until we can properly integrate go-containerregistry inside the builder VM.

Test plan

• Deploy to staging
• Test Python app build (previously failing)
• Test Node.js app build (was working)
• Verify both apps start successfully

Made with Cursor

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Note

Medium Risk
Touches the build completion contract and image conversion/export defaults, which can impact build latency and runtime boot behavior. While largely a revert to a simpler pipeline, regressions could surface in image readiness timing and rootfs mounting assumptions.

Overview
Build completion now always waits for the host-side image conversion pipeline before marking a build ready, addressing a race where the build finished but the image wasn’t usable yet.

This reverts the in-VM EROFS creation/registration path: drops ErofsDiskPath from build results/types, removes createErofsFromRegistry and prebuilt-image registration plumbing, and removes EROFS tooling from the builder image.

Image export defaults are shifted back to ext4 as DefaultImageFormat, and the init overlay setup mounts /dev/vda explicitly as ext4. Separately, the builder image config now defaults to hypeman/builder:latest, and the embedded builder-image Docker build no longer forces --network=host.

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Cursor Bugbot has reviewed your changes and found 1 potential issue.

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Ext4-only mount breaks existing erofs images

High Severity

setupOverlay now mounts /dev/vda as ext4 only. Previously it relied on kernel autodetection, so cached images built as erofs still booted. After this change, any existing erofs rootfs in the image store fails to mount, causing VM boot failures for reused images.

 

[hiroTamada]

this is fine.