WIP: Containerfile: move from build-chunked-oci to chunkah

[jlebon]

Notably this implicitly moves FCOS from OSTree-based to "plain" OCI
images.

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Mostly for demonstration purposes at this point. :)

[gemini-code-assist]

Code Review

This pull request replaces the usage of rpm-ostree experimental compose build-chunked-oci with a new tool, chunkah, for creating the OCI image. This is implemented via a new multi-stage build in the Containerfile. While the approach is sound, I've found a critical issue with incorrect paths in the new build stage that will likely cause the build to fail. My review includes a specific comment and a code suggestion to address this.

[dustymabe]

Not sure I understand the CI failure here:

[2026-01-30T21:20:16.138Z] + cosa osbuild qemu
[2026-01-30T21:20:17.057Z] Will build qemu
[2026-01-30T21:20:17.615Z] error: No such file or directory: /usr/share/coreos-assembler
[2026-01-30T21:20:17.615Z] Traceback (most recent call last):
[2026-01-30T21:20:17.615Z]   File "<string>", line 10, in <module>
[2026-01-30T21:20:17.615Z]     cmdlib.import_ostree_commit(workdir, builddir, buildmeta, extract_json=('1' == '1'))
[2026-01-30T21:20:17.615Z]     ~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[2026-01-30T21:20:17.615Z]   File "/usr/lib/coreos-assembler/cosalib/cmdlib.py", line 323, in import_ostree_commit
[2026-01-30T21:20:17.615Z]     extract_image_json(workdir, commit)
[2026-01-30T21:20:17.615Z]     ~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^
[2026-01-30T21:20:17.615Z]   File "/usr/lib/coreos-assembler/cosalib/cmdlib.py", line 277, in extract_image_json
[2026-01-30T21:20:17.615Z]     raise Exception("Failed to extract image.json")
[2026-01-30T21:20:17.615Z] Exception: Failed to extract image.json
[2026-01-30T21:20:17.615Z] failed to execute cmd-osbuild: exit status 1

[jlebon]

This is now blocked on bootc-dev/bootc#1637.

I will work on fixing that and then adding chunkah to the base fedora-bootc image before we circle back to turning it on in fedora-bootc and here. So, might take some time.