[codex] Add Ubuntu distro VM disk headroom

[Jesssullivan]

Summary

• expand the Ubuntu 24.04 nix-vm-test guest root disk before package validation
• document that the headroom is needed for the broad-feature GTK/WebKit dependency closure

Root cause

The fresh release proof built and signed all Linux artifacts and passed Fedora 42 plus Rocky 10 KVM validation, but Ubuntu 24.04 failed while unpacking the broad-feature DEB dependency closure because the default cloud image ran out of disk space.

Validation

• nix-instantiate --parse nix/tests-distro.nix
• git diff --check

The real KVM package install remains CI-only and should run on the self-hosted runner for this PR.

[greptile-apps]

Greptile Summary

This PR fixes Ubuntu 24.04 KVM test failures caused by the default cloud image running out of disk space when unpacking the GTK/WebKit DEB dependency closure, by adding diskSize = "+8G" to the distro-ubuntu2404 nix-vm-test config. The two documentation files are updated to record the release run that exposed the blocker and update the next-action item accordingly.

Confidence Score: 4/5

Safe to merge; the one-line Nix change uses a documented and valid diskSize syntax, with only a minor open question about whether Debian 12 needs the same treatment.

The fix is minimal and correct — diskSize = "+8G" is explicitly supported by nix-vm-test's reference docs. The only finding is a P2 concern that the identical Debian 12 test installs the same broad-feature DEB but has no disk expansion, which could surface a similar failure in CI.

nix/tests-distro.nix — specifically the distro-debian12 block which lacks a matching diskSize guard

Important Files Changed

Filename	Overview
nix/tests-distro.nix	Adds diskSize = "+8G" to Ubuntu 24.04 VM test config to fix out-of-disk failures when unpacking the GTK/WebKit DEB closure; the identical Debian 12 test still has no disk expansion set.
docs/distro-testing-readiness-plan.md	Documentation update: records release run 25088831284 result and updates the next-action item to reference the Ubuntu disk-headroom fix.
docs/linux-packaging-cd-plan.md	Documentation update: records release run outcome and root cause (Ubuntu cloud image disk exhaustion), consistent with the Nix change.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[Release build: all Linux artifacts] --> B[Fedora 42 KVM ✅]
    A --> C[Rocky 10 KVM ✅]
    A --> D[Ubuntu 24.04 KVM]
    A --> E[Debian 12 KVM]

    D --> F{Default cloud image\ndisk sufficient?}
    F -- No, pre-PR --> G[❌ Out of disk unpacking\nGTK/WebKit DEB closure]
    F -- Yes, post-PR diskSize=+8G --> H[✅ DEB install succeeds]

    E --> I{Default cloud image\ndisk sufficient?}
    I -- Unknown --> J[⚠️ Same DEB closure,\nno diskSize guard added]

    H --> K[Release upload unblocked]

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Comments Outside Diff (1)

1. nix/tests-distro.nix, line 252-272 (link)

   Debian 12 may need the same disk expansion

   distro-debian12 installs the identical cmuxDebDir DEB (the same releaseArtifacts.assets.deb reference) and runs the same apt-get install -f -y dependency resolution, so it pulls in the same GTK/WebKit closure. If Ubuntu 24.04's cloud image was too small, Debian 12's default cloud image could hit the same out-of-space error under the same workload. Worth verifying the Debian 12 image has sufficient headroom, or adding diskSize = "+8G" there as well as a precaution.

_{Reviews (1): Last reviewed commit: "Add Ubuntu distro VM disk headroom" | Re-trigger Greptile}