Install Hasklug font into macOS font dir before PDF build

Tectonic on macOS uses Core Text, which only scans
~/Library/Fonts/ and the system font dirs — it can't see fonts
provided via Nix's /nix/store. Copy the Hasklug Nerd Font files
into ~/Library/Fonts/ on the CI runner before invoking the PDF
build so fontspec can resolve 'Hasklug Nerd Font Mono'.

Author: ad-si

.github/workflows/build-artifacts.yml

@@ -33,6 +33,19 @@ jobs:
       - name: Check Nix Flake
         run: nix flake check
 
+      - name: Make Hasklug font visible to tectonic
+        run: |
+          # nix develop realizes all dev-shell inputs into /nix/store
+          nix develop --command true
+          mkdir -p ~/Library/Fonts
+          for dir in /nix/store/*-nerd-fonts-hasklug-*/share/fonts; do
+            [ -d "$dir" ] || continue
+            find "$dir" -type f \( -name "*.otf" -o -name "*.ttf" \) \
+              -exec cp -n {} ~/Library/Fonts/ \;
+          done
+          echo "Installed fonts:"
+          ls ~/Library/Fonts/ | grep -i hasklug | head
+
       - name: Build Anki deck and PDF with Nix
         run: |
           nix develop --command bash -c \