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ADR-0017: Standard GitHub-hosted CI runners

Context and scope

ADR-0009 introduced a repository-owned runner image and a self-hosted runner profile to reduce repeated SDK and NativeAOT setup on ephemeral workers. Foundry is a public repository, and GitHub documents standard GitHub-hosted runners as free and unlimited for public repositories. Maintaining separate runner capacity therefore adds infrastructure, routing, image-publication, and trust-boundary complexity without reducing GitHub Actions runner charges.

GitHub's public-repository runner table explicitly includes both ubuntu-24.04 and windows-latest. Larger runners are a separate product and are always billed, including for public repositories.

This decision governs repository workflow runner selection, portable toolchain setup, and live-model execution boundaries. It does not prohibit developers from running deterministic repository commands on their own machines.

Decision drivers

  • Use the free public-repository compute GitHub already provides.
  • Make the runner class visible from each workflow without repository settings.
  • Prevent a variable or custom label from silently selecting paid capacity.
  • Preserve exact SDK, required-check, release-permission, and fork-isolation behavior.
  • Keep live-model execution out of repository CI/CD.
  • Make future Windows workflow selection unambiguous.

Decision

Every Foundry workflow uses a literal standard GitHub-hosted runner label. Linux jobs use ubuntu-24.04. A future Windows job uses windows-latest. Both labels are in GitHub's standard public-repository runner table and inherit the documented free and unlimited public-repository usage terms.

Foundry does not use:

  • self-hosted runners or runner groups;
  • repository-variable runner overrides;
  • repository-owned runner images or profiles;
  • GitHub-hosted larger runners; or
  • repository workflows that invoke a live LLM.

The repository setup action remains responsible for validating and installing the exact SDKs requested by each job. NativeAOT jobs install their Linux prerequisites on the hosted VM.

scripts/test-ci-contract.ps1 enforces the allowed runner labels, rejects the removed routing mechanisms, preserves required check names and release permissions, and exercises windows-latest as an accepted mutation. The guidance contract rejects every live-LLM workflow. Live Copilot integration tests may run only as explicitly approved local operations and skip when GITHUB_ACTIONS=true.

Alternatives considered

Keep the self-hosted runner path

Prebuilt workers can reduce setup time and provide direct capacity control. They also require external hosts, image and profile lifecycle management, registration trust, routing variables, and operator recovery. That cost is not justified while standard public-repository runners are free and unlimited.

Keep a runner override with a hosted default

A repository variable would preserve deployment flexibility. It would also hide the actual runner class from review and allow a settings change to route jobs to custom or paid capacity without changing workflow source. Literal labels provide a stronger and simpler contract.

Use GitHub-hosted larger runners

Larger runners could shorten broad builds and NativeAOT publication. GitHub states that larger runners are always billed, even for public repositories. Foundry prefers the standard runner unless measured evidence later justifies a separate accepted decision.

Consequences

Positive

  • Standard Linux and Windows capacity is free and unlimited for this public repository.
  • Pull requests, trusted pushes, documentation, and releases use the same GitHub-managed trust boundary.
  • Runner selection is reviewable directly in workflow source.
  • No custom runner image, profile, or host requires maintenance.

Negative

  • Clean hosted VMs reinstall missing SDKs and NativeAOT prerequisites.
  • Jobs may take longer than equivalent prebuilt workers.
  • Repository CI cannot host live-model evaluation.

Neutral

  • Current workflows remain Linux-only.
  • Public package, artifact, cache, and release-asset policies remain separate from runner selection.
  • Required check names and release publishing behavior remain unchanged.

Confirmation

The decision is confirmed when:

  • every workflow uses only ubuntu-24.04 or windows-latest;
  • the CI contract and guidance self-tests pass;
  • the repository runner override is no longer used;
  • the self-hosted profile, custom image, image workflow, and live-model workflow are absent; and
  • required pull-request checks pass on GitHub-hosted runners.

References