Add CI builder image and use it in the pipeline

builder.Dockerfile bakes the export step's dependencies into
git.teletype.hu/internal/love-builder and pre-fetches love.js to
/opt/lovejs.zip; the Makefile prefers the cached copy and falls
back to downloading from GitHub outside the image.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

README.md

@@ -29,4 +29,20 @@ The pipeline uploads `$(PROJECT)-$(VERSION).love.zip`,
 the droparea, then triggers `/update` twice: once with `platform=love`
 (desktop package) and once with `platform=love-web` (web build).
 
+## Builder image
+
+`builder.Dockerfile` bakes the pipeline's export-step dependencies
+(zip/unzip/curl/make + `luac` for the syntax check) into
+`git.teletype.hu/internal/love-builder`, and pre-fetches love.js to
+`/opt/lovejs.zip` — the Makefile uses the cached copy when present
+and only falls back to downloading from GitHub outside the image:
+
+```sh
+docker build --platform linux/amd64 -f builder.Dockerfile \
+  -t git.teletype.hu/internal/love-builder:latest .
+docker push git.teletype.hu/internal/love-builder:latest
+```
+
+Rebuild the image to pick up a newer love.js snapshot.
+
 Detailed documentation lives on the wiki: `/development/love`.

builder.Dockerfile

@@ -0,0 +1,21 @@
+# CI builder image for Love2D projects: packaging tools + luac syntax check,
+# with love.js pre-fetched to /opt/lovejs.zip so `make web` does not hit
+# GitHub on every pipeline run (the Makefile falls back to curl elsewhere).
+#
+# Build & push (the CI runner is linux/amd64):
+#   docker build --platform linux/amd64 -f builder.Dockerfile \
+#     -t git.teletype.hu/internal/love-builder:latest .
+#   docker push git.teletype.hu/internal/love-builder:latest
+
+FROM alpine:3.22
+
+RUN apk add --no-cache make zip unzip curl git lua5.4 \
+ && ln -sf /usr/bin/lua5.4 /usr/bin/lua \
+ && ln -sf /usr/bin/luac5.4 /usr/bin/luac
+
+RUN curl -sSL https://github.com/2dengine/love.js/archive/refs/heads/master.zip \
+      -o /opt/lovejs.zip
+
+WORKDIR /workspace
+
+CMD ["/bin/sh"]

example-makefile.make

@@ -14,6 +14,11 @@ OUTPUT_WEB_ZIP  = $(PROJECT)-$(VERSION).html.zip
 
 VERSION_FILE = .version
 
+# The love-builder CI image pre-fetches love.js here; local builds fall
+# back to downloading it from GitHub.
+LOVEJS_URL   = https://github.com/2dengine/love.js/archive/refs/heads/master.zip
+LOVEJS_CACHE = /opt/lovejs.zip
+
 all: build
 
 build:
@@ -35,8 +40,13 @@ love:
 
 web: love
 	@mkdir -p $(WEB_DIR)
-	@echo "==> Downloading love.js (2dengine)"
-	curl -sSL https://github.com/2dengine/love.js/archive/refs/heads/master.zip -o $(DIST_DIR)/lovejs.zip
+	@if [ -f $(LOVEJS_CACHE) ]; then \
+		echo "==> Using cached love.js ($(LOVEJS_CACHE))"; \
+		cp $(LOVEJS_CACHE) $(DIST_DIR)/lovejs.zip; \
+	else \
+		echo "==> Downloading love.js (2dengine)"; \
+		curl -sSL $(LOVEJS_URL) -o $(DIST_DIR)/lovejs.zip; \
+	fi
 	unzip -o $(DIST_DIR)/lovejs.zip -d $(DIST_DIR)/lovejs-src
 	rm -f $(DIST_DIR)/lovejs.zip
 	@echo "==> Assembling web bundle"

example-woodpecker.yaml

@@ -6,9 +6,8 @@ steps:
       - make ci-version
 
   - name: export
-    image: alpine
+    image: git.teletype.hu/internal/love-builder:latest
     commands:
-      - apk add --no-cache zip make curl unzip
       - make ci-export
 
   - name: upload