2026-07-15

Pin macOS OSS CI to macos-14 to unbreak Build and test

Summary:
The `macos-build-and-test` job in the OSS "Build and test" workflow (and the sibling `macos-build-examples` job in "Build and Examples") regressed again after GitHub's `macos-latest` label advanced to the `macos-15` runner image. On `macos-15`, `xcode-version: latest-stable` selects an Xcode/SDK that mis-targets the deployment SDK and breaks the `cargo build` step (see actions/runner-images#12758).

This matches the reported "recently regressed, previously recovered" pattern: switching the pin to `latest-stable` in `Use latest stable Xcode in OSS CI` briefly recovered the job while `macos-latest` still resolved to `macos-14`, then it re-broke once the label rolled forward to `macos-15`.

Pin `runs-on: macos-14` in both `build-and-test.yml` and `build-and-examples.yml`, where `latest-stable` resolves to a known-good Xcode 16.x. This is the documented remedy and is trivially reversible once the `macos-15` image is fixed upstream.

This is a GitHub-hosted-runner-image regression, not a buck2 code bug — internal macOS builds use Meta's own toolchains and stayed green, which is why it was not caught by internal signal.

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Differential Revision: D111806260

fbshipit-source-id: d827c7eb21750faff519ece8be81a81a6f16eaa6