Summary

The :darwin: 26 aarch64 - test-bun Buildkite jobs are failing on most PR builds. The runner never starts a single test; it fails downloading the build artifact:

Error: buildkite-agent artifact download timed out after 120s for step 'darwin-aarch64-build-bun'. Refusing to continue with a partial download (would silently fall back to the wrong binary).
    at getExecPathFromBuildKite (file:///Users/administrator/Library/Services/buildkite-agent/builds/darwin-aarch64-26-5-1-1/bun/bun/scripts/runner.node.mjs:2182:13)
    at async runTests (.../scripts/runner.node.mjs:481:16)

Scope

Of the 30 most recent failed/failing builds on the bun pipeline, 22 have a failed :darwin: 26 aarch64 - test-bun job, across unrelated branches. All of them hit the same artifact download timeout:

I saw it reproduce on two consecutive builds of the same PR (66995 and 67012), both on the agent darwin-aarch64-26-5-1-1, about 35 minutes apart. So it is not a one-off blip.

Likely causes

• The darwin-aarch64-26 agent fleet (or just darwin-aarch64-26-5-1-1) has slow or broken connectivity to the Buildkite artifact store, so the 120s download budget in scripts/runner.node.mjs:getExecPathFromBuildKite is not enough.
• Or the darwin-aarch64-build-bun artifacts are larger or slower to serve than they used to be.

Impact

Every PR that lands on an affected agent goes red on a lane that ran zero tests, which both hides real failures and blocks merges. The job does not get an automatic Buildkite retry (exit status 1 from the runner), so each occurrence needs a manual "Retry job" click.