Migrate from Namespace to runnerhut

What Namespace does well

• Goes far beyond CI — devboxes, sandboxes and ephemeral clusters in one platform
• Serious Bazel support including remote execution and build observability
• Egress policy and audit logging are first-class, not add-ons
• Credible engineering customers including Zed, DuckDB and Framer

Where we differ

• Platform breadth means CI is one product among many, not the whole focus
• 221 of their 300 indexed pages are docs — little help while you are still evaluating
• Nearly half their blog is changelog entries rather than durable guidance

The migration

jobs:
  build:
-   runs-on: nscloud-ubuntu-22.04-amd64-4x8
+   runs-on: runnerhut-8vcpu-ubuntu-2404
    steps:
      - uses: actions/checkout@v4

And the migration back

We publish this because after BuildJet's shutdown, "what if you disappear" is a fair question. Leaving is the same single line you changed to arrive.

jobs:
  build:
-   runs-on: runnerhut-8vcpu-ubuntu-2404
+   runs-on: ubuntu-latest

Checklist

1. Install the runnerhut GitHub App on the repositories you want to move
2. Change runs-on in one job first and compare timings against the old runner
3. Add runner.arch to cache keys if you are also moving to arm64
4. Roll out to the rest of the repository once the comparison looks right
5. Set a budget cap and concurrency cancellation before going organisation-wide