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

@@ -27,6 +27,19 @@ spirit as [tic80-tools](../tic80-tools).
    `droparea_ssh_password` / `update_secret_key` secrets in Woodpecker.
 4. Copy `example-tasks.json` to `.vscode/tasks.json`.
 
+## Builder image
+
+`builder.Dockerfile` bakes the pipeline's build-step dependencies
+(ACME assembler + make) into `git.teletype.hu/internal/c64-builder`,
+so the build step no longer runs `apt-get` on every run (VICE is a
+local-dev tool only and is not included):
+
+```sh
+docker build --platform linux/amd64 -f builder.Dockerfile \
+  -t git.teletype.hu/internal/c64-builder:latest .
+docker push git.teletype.hu/internal/c64-builder:latest
+```
+
 The pipeline uploads `$(PROJECT)-$(VERSION).prg` and
 `$(PROJECT)-$(VERSION).metadata.json` to the droparea, then triggers
 `/update?platform=c64&name=$(PROJECT)&version=$(VERSION)`, which

builder.Dockerfile

@@ -0,0 +1,18 @@
+# CI builder image for C64 projects: ACME assembler + make, so the
+# pipeline's build step does not run apt-get on every run. The VICE
+# emulator is a local-dev tool only and is intentionally not included.
+#
+# Build & push (the CI runner is linux/amd64):
+#   docker build --platform linux/amd64 -f builder.Dockerfile \
+#     -t git.teletype.hu/internal/c64-builder:latest .
+#   docker push git.teletype.hu/internal/c64-builder:latest
+
+FROM debian:stable-slim
+
+RUN apt-get update \
+ && apt-get install -y --no-install-recommends make acme zip curl ca-certificates \
+ && rm -rf /var/lib/apt/lists/*
+
+WORKDIR /workspace
+
+CMD ["/bin/bash"]

example-woodpecker.yaml

@@ -6,9 +6,8 @@ steps:
       - 'make ci-version'
 
   - name: build
-    image: debian:stable-slim
+    image: git.teletype.hu/internal/c64-builder:latest
     commands:
-      - 'apt-get update && apt-get install -y --no-install-recommends make acme'
       - 'make ci-build'
 
   - name: artifact