Skip already-cached packages in CI build-and-cache job

.gitea/workflows/ci.yml

@@ -56,9 +56,20 @@ jobs:
           )
 
           FAILED=()
+          SKIPPED=()
           for pkg in "${PACKAGES[@]}"; do
             echo "::group::Building $pkg"
-            # Capture build output, extract store path (last line starting with /nix/store/)
+
+            # Check if package is already cached by evaluating its store path and checking the remote
+            OUT_PATH=$(nix build ".#$pkg" --no-link --print-out-paths --dry-run 2>/dev/null | grep '^/nix/store/' | tail -1)
+            if [ -n "$OUT_PATH" ] && ssh -i ~/.ssh/cache_key ${{ secrets.CACHE_USER }}@${{ secrets.CACHE_HOST }} \
+                "nix path-info '$OUT_PATH' >/dev/null 2>&1"; then
+              echo "⏭ $pkg already cached ($OUT_PATH), skipping"
+              SKIPPED+=("$pkg")
+              echo "::endgroup::"
+              continue
+            fi
+
             # --cores 2 limits parallel jobs to reduce RAM pressure on john-endesktop
             if BUILD_OUTPUT=$(nix build ".#$pkg" --no-link --print-out-paths --cores 2 2>&1); then
               OUT_PATH=$(echo "$BUILD_OUTPUT" | grep '^/nix/store/' | tail -1)
@@ -84,6 +95,10 @@ jobs:
             echo "::endgroup::"
           done
 
+          if [ ${#SKIPPED[@]} -gt 0 ]; then
+            echo "Skipped (already cached): ${SKIPPED[*]}"
+          fi
+
           if [ ${#FAILED[@]} -gt 0 ]; then
             echo "::error::Failed packages: ${FAILED[*]}"
             exit 1