Stage build artifacts so Nix flake can see them

Nix flakes only see git-tracked files. Since build/ is gitignored,
the pre-built artifacts were invisible to the flake evaluation,
causing it to fall through to the stub derivation. Fix by staging
with git add -f before nix build.

Author: d-buckner

.github/workflows/build-iso.yml

@@ -44,6 +44,9 @@ jobs:
           npm run build --workspace=services/host-agent/web
           cp -r services/host-agent/web/build build/frontend
 
+      - name: Stage build artifacts for Nix
+        run: git add -f build/
+
       - name: Install Nix
         uses: cachix/install-nix-action@v27
         with:

claude.md

@@ -200,6 +200,7 @@ mkdir -p build
 cd services/host-agent && CGO_ENABLED=0 GOOS=linux GOARCH=amd64 go build -o ../../build/host-agent ./cmd/host-agent
 cd ../.. && npm ci && npm run build --workspace=services/host-agent/web
 cp -r services/host-agent/web/build build/frontend
+git add -f build/   # Nix flakes only see git-tracked files
 nix build .#packages.x86_64-linux.iso
 ```