Add CI builder image and use it in the pipeline

builder.Dockerfile bakes the build step's dependencies into
git.teletype.hu/internal/* so the pipeline no longer installs
packages on every run.

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

README.md

@@ -29,13 +29,27 @@ and [tic80-tools](../tic80-tools).
    in sync with `EXPORT_PRESET` in the Makefile.
 3. Copy `example-woodpecker.yaml` to `.woodpecker.yaml` and add the
    `droparea_ssh_password` / `update_secret_key` secrets in Woodpecker.
-   Match the `barichello/godot-ci` image tag to the Godot version the
-   project is made with (e.g. `4.6`) — the image ships the matching
-   export templates.
+   Match the `godot-builder` image tag to the Godot version the
+   project is made with (e.g. `4.6`) — the underlying
+   `barichello/godot-ci` image ships the matching export templates.
 4. Copy `example-tasks.json` to `.vscode/tasks.json`.
 
 The pipeline uploads `$(PROJECT)-$(VERSION).html.zip` to the droparea,
 then triggers
 `/update?platform=godot&name=$(PROJECT)&version=$(VERSION)`.
 
+## Builder image
+
+`builder.Dockerfile` wraps `barichello/godot-ci` (editor + web export
+templates) with make/zip preinstalled as
+`git.teletype.hu/internal/godot-builder`, so the build step no longer
+runs `apt-get` on every run. The tag tracks the Godot version:
+
+```sh
+docker build --platform linux/amd64 -f builder.Dockerfile \
+  --build-arg GODOT_VERSION=4.6 \
+  -t git.teletype.hu/internal/godot-builder:4.6 .
+docker push git.teletype.hu/internal/godot-builder:4.6
+```
+
 Detailed documentation lives on the wiki: `/development/godot`.

builder.Dockerfile

@@ -0,0 +1,20 @@
+# CI builder image for Godot projects: barichello/godot-ci (editor + web
+# export templates) with make/zip preinstalled, so the pipeline's build step
+# does not run apt-get on every run.
+#
+# Keep the tag in sync with the Godot version the projects use.
+#
+# Build & push (the CI runner is linux/amd64):
+#   docker build --platform linux/amd64 -f builder.Dockerfile \
+#     --build-arg GODOT_VERSION=4.6 \
+#     -t git.teletype.hu/internal/godot-builder:4.6 .
+#   docker push git.teletype.hu/internal/godot-builder:4.6
+
+ARG GODOT_VERSION=4.6
+FROM barichello/godot-ci:${GODOT_VERSION}
+
+RUN apt-get update \
+ && apt-get install -y --no-install-recommends make zip jq \
+ && rm -rf /var/lib/apt/lists/*
+
+WORKDIR /workspace

example-woodpecker.yaml

@@ -6,9 +6,8 @@ steps:
       - make ci-version
 
   - name: build
-    image: barichello/godot-ci:4.6
+    image: git.teletype.hu/internal/godot-builder:4.6
     commands:
-      - apt-get update && apt-get install -y --no-install-recommends make zip
       - make ci-export
 
   - name: artifact