From 6fcb25bcd97f5042d1e93969c6dc94bfd2cd0f25 Mon Sep 17 00:00:00 2001
From: JacobPEvans <20714140+JacobPEvans@users.noreply.github.com>
Date: Sun, 15 Mar 2026 11:34:07 -0400
Subject: [PATCH 1/2] feat(ci): add reusable copilot-setup-steps workflow +
 regression comments

Create _copilot-setup-steps.yml reusable workflow for Nix-based Copilot
coding agent environment setup. This centralizes the copilot setup that
was copy-pasted across nix-home, nix-darwin, and nix-ai repos.

Add regression-prevention comments to _nix-build.yml and _nix-validate.yml
clarifying that determinate-nix-action@v3 is ONLY a Nix installer and does
NOT include flake checking (prevents future AI-assisted regressions from
stale training data conflating the two actions).

(claude)
---
 .github/workflows/_copilot-setup-steps.yml | 24 ++++++++++++++++++++++
 .github/workflows/_nix-build.yml           |  2 ++
 .github/workflows/_nix-validate.yml        |  3 +++
 3 files changed, 29 insertions(+)
 create mode 100644 .github/workflows/_copilot-setup-steps.yml

diff --git a/.github/workflows/_copilot-setup-steps.yml b/.github/workflows/_copilot-setup-steps.yml
new file mode 100644
index 0000000..6139a74
--- /dev/null
+++ b/.github/workflows/_copilot-setup-steps.yml
@@ -0,0 +1,24 @@
+# Reusable: Copilot Setup Steps (Nix)
+# Sets up a Nix development environment for GitHub Copilot coding agents.
+#
+# IMPORTANT — Action clarification (prevents regression from stale AI training data):
+# - determinate-nix-action@v3 is ONLY a Nix installer (replaced nix-installer-action@v21)
+# - It does NOT include flake checking — that is a separate action (flake-checker-action)
+# - For copilot setup, only the installer is needed (CI handles flake validation)
+name: _copilot-setup-steps
+
+on:
+  workflow_call:
+
+jobs:
+  copilot-setup-steps:
+    name: Copilot Setup Steps
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+    steps:
+      - uses: actions/checkout@v6
+
+      # Installs Nix only. Does NOT validate flakes.
+      # Replaced nix-installer-action@v21 (Node.js 20, deprecated June 2026).
+      - uses: DeterminateSystems/determinate-nix-action@v3
diff --git a/.github/workflows/_nix-build.yml b/.github/workflows/_nix-build.yml
index 465169b..4b62fb3 100644
--- a/.github/workflows/_nix-build.yml
+++ b/.github/workflows/_nix-build.yml
@@ -26,6 +26,8 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v6
 
+      # determinate-nix-action@v3 is ONLY a Nix installer (replaced nix-installer-action@v21).
+      # It does NOT include flake checking — flake validation is in _nix-validate.yml.
       - name: Install Nix
         uses: DeterminateSystems/determinate-nix-action@v3
         with:
diff --git a/.github/workflows/_nix-validate.yml b/.github/workflows/_nix-validate.yml
index 365327b..b405574 100644
--- a/.github/workflows/_nix-validate.yml
+++ b/.github/workflows/_nix-validate.yml
@@ -20,6 +20,9 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v6
 
+      # determinate-nix-action@v3 is ONLY a Nix installer (replaced nix-installer-action@v21).
+      # It does NOT include flake checking — that was a separate action (flake-checker-action).
+      # Flake evaluation is handled by `nix flake check` below, not by the installer.
       - name: Install Nix
         uses: DeterminateSystems/determinate-nix-action@v3
         with:

From e550b7c811c4074b62fa270b6d4f847e6eac4474 Mon Sep 17 00:00:00 2001
From: Jacob <20714140+JacobPEvans@users.noreply.github.com>
Date: Sun, 15 Mar 2026 15:09:13 -0400
Subject: [PATCH 2/2] Potential fix for pull request finding

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>
Signed-off-by: Jacob <20714140+JacobPEvans@users.noreply.github.com>
---
 .github/workflows/_copilot-setup-steps.yml | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/.github/workflows/_copilot-setup-steps.yml b/.github/workflows/_copilot-setup-steps.yml
index 6139a74..3255f83 100644
--- a/.github/workflows/_copilot-setup-steps.yml
+++ b/.github/workflows/_copilot-setup-steps.yml
@@ -7,6 +7,10 @@
 # - For copilot setup, only the installer is needed (CI handles flake validation)
 name: _copilot-setup-steps
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
 on:
   workflow_call: