Add reusable Copilot setup workflow with Nix and UV caching

[Copilot]

Creates .github/workflows/copilot-setup-steps.yml as a reusable workflow for Copilot environment setup.

Implementation

• Nix environment: cachix/install-nix-action@v31 with nixos-unstable channel, activated via nicknovitski/nix-develop@v1
  • Python 3.11 and UV are provided by the Nix shell (defined in shell.nix)
• UV caching: Explicit cache action for .venv and ~/.cache/uv keyed on uv.lock hash
• Workflow triggers:
  • workflow_call for composition by other workflows
  • workflow_dispatch for manual runs
  • pull_request for automatic validation when AGENTS.md or the workflow file itself is modified

Usage

jobs:
  my-job:
    uses: ./.github/workflows/copilot-setup-steps.yml

Original prompt

Create a .github/workflows/copilot-setup-steps.yml

It should start with

  - name: Checkout code
    uses: actions/checkout@v4

  - name: Install Nix
    uses: cachix/install-nix-action@v31
    with:
      nix_path: nixpkgs=channel:nixos-unstable

  - uses: nicknovitski/nix-develop@v1

Then install and cache the UV dependencies

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[ncrmro]

@copilot Remove the setup python/uv, UV and python are installed via the nix shell

[Copilot]

@copilot Remove the setup python/uv, UV and python are installed via the nix shell

Done in 9ac2c34. The workflow now uses Python and UV from the Nix shell via nix-develop, removing the redundant setup steps.

[github-actions]

Thank you for your submission, we really appreciate it. Like many open-source projects, we ask that you all sign our Developer Certificate of Origin before we can accept your contribution. You can sign the DCO by just posting a Pull Request Comment same as the below format.

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I have read the CLA Document and I hereby sign the CLA

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2 out of 3 committers have signed the DCO.
✅ (ncrmro)[https://github.com/ncrmro]
✅ (nhorton)[https://github.com/nhorton]
❌ @copilot
_{You can retrigger this bot by commenting recheck in this Pull Request. Posted by the DCO Assistant Lite bot.}

[ncrmro]

@copilot this should run on PR's that change the instructions filel

[Copilot]

@copilot this should run on PR's that change the instructions filel

Done in e9d7bac. The workflow now triggers on PRs that modify AGENTS.md (the agent instructions file) or the workflow file itself.

[ncrmro]

This is blocked until we can get in the Nix Flake (I hoped the shell would work)