Overview

Add riscv64 as a supported image architecture, treating it like arm64 (self-contained runner tarball, no system dotnet needed in the image).

The riscv64 GitHub Actions runner tarball is a self-contained build produced from the canonical/github-actions-runner fork (with a riscv64 patch) using the community dotnet-sdk-riscv snap at build time. The produced tarball bundles its own .NET runtime, so — unlike s390x/ ppc64le — no dotnet-runtime apt package is installed in the runner image and riscv64 is excluded from S390X_PPC64LE_ADDITIONAL_APT_PACKAGES.

Changes:

config.py (app):
  - Add RISCV64 to the Arch enum and Arch.to_openstack().
  - Add RUNNER_BINARY_REPO_OVERRIDES to publish the runner tarball from a fork until it is folded into the canonical fork's release pipeline (riscv64 -> vhaudiquet/actions-runner-riscv).

cloud_image.py (app):
  - Map Arch.RISCV64 -> "riscv64" in _get_supported_runner_arch() and add it to SupportedBaseImageArch.

openstack_builder.py (app):
  - _generate_cloud_init_script resolves the runner binary repo via the per-arch override (falling back to canonical/github-actions-runner).
  - Refactor initialize() to iterate over the supported bases, skipping focal for riscv64 (no riscv64 focal cloud image exists on cloud-images.ubuntu.com).

state.py (charm):
  - Add RISCV64 to the charm-side Arch enum, ARCHITECTURES_RISCV64 set, and Arch.from_charm().

charmcraft.yaml:
  - Document riscv64 in the architecture config option description.

Tests:

• Add riscv64 parametrized cases across the app and charm unit tests.
• Add test_initialize_riscv64_skips_focal covering the focal skip.

Rationale

RISCV64 hardware will be coming to Toronto and then PS10. We need all Canonical and other software to be fully supported for this. A lot of software is using GitHub runners for tests and build. We need to support GitHub runners, but they themselves depend on .NET which depends on hardware builders. So we need to break the chain by bootstrapping something.

Juju Events Changes

None. No Juju events or hooks were modified. The change is internal to the build logic and configuration parsing.

Module Changes

• src/state.py
• app/src/github_runner_image_builder/config.py
• app/src/github_runner_image_builder/cloud_image.py
• app/src/github_runner_image_builder/openstack_builder.py

(see full change description above)

Library Changes

None.

Checklist

• The charm style guide was applied
• The contributing guide was applied
• The changes are compliant with ISD054 - Managing Charm Complexity
• The documentation for charmhub is updated.
• The PR is tagged with appropriate label (urgent, trivial, senior-review-required, documentation)
• The docs/changelog.md is updated with user-relevant changes in the format of keep a changelog v1.1.0
• The application version is incremented in app/pyproject.toml

Still WIP, will try to comply with all requirements above