Install node, yarn and python from the distribution (closes #146)

Follows sneak's ruling at
#146 (comment). Runtimes
and the installer tools bundled with python come from the distribution,
with no version and no hash. Third-party packages stay pinned by hash.

script/bootstrap drops nvm and corepack. It installs node, yarn and the
node packages only when yarn.lock is in the tree, and stops there when
yarn's major version is not 1. This repository's Dockerfile starts from
Alpine 3.24. The Python example starts from debian:trixie-slim, keeps
pipenv at $HOME/.pipenv on a host and in an image, and sets
PIP_ONLY_BINARY=:all:, so pip downloads no build tools without a hash
check.

Model: opus-5-5

Dockerfile

@@ -2,11 +2,15 @@
 # lint` or `script/lint`, which are themselves a docker build and would
 # recurse into a daemon that does not exist in a build step.
 #
-# Every stage declares ARG CACHEBUST first: script/ passes a new value on
-# every build, which reruns every RUN step after it.
+# In every stage, ARG CACHEBUST comes right after the step that installs
+# system packages. script/ passes a new value on every build. That value
+# reruns every RUN step below the ARG line, and the install step keeps
+# its layer. node and yarn come from the distribution, which is trusted,
+# so they need no version and no hash.
 #
-# node 22-alpine, 2026-02-22
-FROM node@sha256:e4bf2a82ad0a4037d28035ae71529873c069b13eb0455466ae0bc13363826e34 AS lint
+# alpine 3.24.3, 2026-11-04
+FROM alpine@sha256:be2656061b536c1883c4034790e21d0a09c5aaaf51968b89368a3c0371ea2c9a AS lint
+RUN apk add --no-cache git make nodejs yarn
 ARG CACHEBUST
 
 WORKDIR /app
@@ -21,8 +25,9 @@ RUN yarn run prettier --check '**/*.md' --tab-width 4 --prose-wrap always
 
 # Test phase, same shape and for the same reason.
 #
-# node 22-alpine, 2026-02-22
-FROM node@sha256:e4bf2a82ad0a4037d28035ae71529873c069b13eb0455466ae0bc13363826e34 AS test
+# alpine 3.24.3, 2026-11-04
+FROM alpine@sha256:be2656061b536c1883c4034790e21d0a09c5aaaf51968b89368a3c0371ea2c9a AS test
+RUN apk add --no-cache git make nodejs yarn
 ARG CACHEBUST
 
 WORKDIR /app
@@ -41,8 +46,9 @@ RUN echo "No tests defined."
 # this image cannot be produced unless lint and test passed. A stage
 # appended after this one would drop all three out of a plain build.
 #
-# node 22-alpine, 2026-02-22
-FROM node@sha256:e4bf2a82ad0a4037d28035ae71529873c069b13eb0455466ae0bc13363826e34
+# alpine 3.24.3, 2026-11-04
+FROM alpine@sha256:be2656061b536c1883c4034790e21d0a09c5aaaf51968b89368a3c0371ea2c9a
+RUN apk add --no-cache git make nodejs yarn
 ARG CACHEBUST
 
 WORKDIR /app
@@ -50,8 +56,8 @@ WORKDIR /app
 COPY --from=lint /app/package.json /dev/null
 COPY --from=test /app/package.json /dev/null
 
-# script/bootstrap installs all prerequisites. Manifests are copied
-# first so that layer stays cached until dependencies change.
+# script/bootstrap finds the system packages above and installs the node
+# packages.
 COPY script/ script/
 COPY package.json yarn.lock ./
 RUN script/bootstrap