Commit yarn 4 in the tree and install with --immutable (closes #149)

Follows sneak's ruling at
#149 (comment). This
repository now carries yarn 4.18.1 under .yarn/releases. The
distribution's yarn only starts that file, and that file does the work.
yarn.lock is converted once, and script/bootstrap installs with
--immutable instead of stopping on yarn's major version. Node is the
distribution's newest Node package: nodejs-current on Alpine and
nodejs_latest on nix. Every Dockerfile stage that needs yarn also copies
.yarnrc.yml and .yarn/releases/. The policies and both checklists say
so, with the steps for converting and for a new repository.

Model: opus-5-5

.dockerignore

@@ -35,6 +35,12 @@
 # `services/api/.claude/` and must add its own anchored entry.
 .claude
 
+# yarn's install state and cache stay out, and its release file stays
+# in. Docker obeys the last matching line, so these two lines sit above
+# the secret patterns, which must win under .yarn/releases/.
+.yarn/*
+!.yarn/releases
+
 # Environment files. `*.env` covers bare `.env` and the `prod.env`
 # convention. Re-include a committed template with a negation if the
 # build needs one: `!docs/example.env`.

.gitattributes

@@ -2,3 +2,6 @@
 # both sides instead of conflicting. Git never reports a conflict here: read
 # the merged entries after every merge or rebase.
 TODO.md merge=union
+
+# yarn's release file is one opaque file in diffs and merges.
+.yarn/releases/** binary

.gitignore

@@ -19,10 +19,12 @@ Thumbs.db
 
 # Node
 node_modules/
+.yarn/*
+!.yarn/releases
 
-# Secrets. Unanchored like every entry above, so each matches at every
-# depth. Matching is case-sensitive on Linux, so names use character
-# ranges rather than a lowercase form that misses `Server.Key`.
+# Secrets. Unanchored, so each matches at every depth. Matching is
+# case-sensitive on Linux, so names use character ranges rather than a
+# lowercase form that misses `Server.Key`.
 
 # Environment files. `*.env` covers bare `.env` and the `prod.env`
 # convention. Only the templates `example.env` and `sample.env` are

.prettierignore

@@ -1,2 +1,3 @@
 node_modules/
+.yarn/
 yarn.lock

.yarnrc.yml

@@ -0,0 +1,5 @@
+enableTelemetry: false
+
+nodeLinker: node-modules
+
+yarnPath: .yarn/releases/yarn-4.18.1.cjs

Dockerfile

@@ -2,17 +2,24 @@
 # 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. That yarn only starts the release
+# file in .yarn/releases/, so every stage copies that file and
+# .yarnrc.yml before it runs script/bootstrap.
 #
-# 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-current yarn
 ARG CACHEBUST
 
 WORKDIR /app
 
 COPY script/ script/
-COPY package.json yarn.lock ./
+COPY package.json yarn.lock .yarnrc.yml ./
+COPY .yarn/releases/ .yarn/releases/
 RUN script/bootstrap
 
 COPY . .
@@ -21,14 +28,16 @@ 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-current yarn
 ARG CACHEBUST
 
 WORKDIR /app
 
 COPY script/ script/
-COPY package.json yarn.lock ./
+COPY package.json yarn.lock .yarnrc.yml ./
+COPY .yarn/releases/ .yarn/releases/
 RUN script/bootstrap
 
 COPY . .
@@ -41,8 +50,9 @@ 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-current yarn
 ARG CACHEBUST
 
 WORKDIR /app
@@ -50,10 +60,11 @@ 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 ./
+COPY package.json yarn.lock .yarnrc.yml ./
+COPY .yarn/releases/ .yarn/releases/
 RUN script/bootstrap
 
 COPY . .

README.md

@@ -111,7 +111,7 @@ development workflow, and the Makefile targets are thin shims that call them.
 The scripts are POSIX sh (not bash) so they run in minimal containers such as
 alpine. We provide:
 
-- `script/bootstrap` — install all dependencies (yarn install)
+- `script/bootstrap` — install all dependencies (`yarn install --immutable`)
 - `script/setup` — set up the repo for development after a fresh clone: runs
   `script/bootstrap`, then `script/install-precommit`
 - `script/projectname` — output the project name (our own extension); used by
@@ -156,9 +156,9 @@ A stage with none of these steps declares `ARG CACHEBUST` right after `FROM`.
 The `script/` builds pass a new `CACHEBUST` value on every build, which reruns
 every `RUN` step after that line and leaves the layers above it and the cache
 mounts in place; `--no-cache` would build those layers again and empty the
-mounts. This repo's own `Dockerfile` declares `ARG CACHEBUST` right after `FROM`
-in every stage: each stage installs system packages and node packages together
-in one `script/bootstrap` step, and check builds may keep system packages but
+mounts. This repo's own `Dockerfile` installs git, make, node and yarn right
+after `FROM` in every stage, above `ARG CACHEBUST`. `script/bootstrap` installs
+the node packages below that line, because check builds keep system packages but
 not node packages.
 
 ## Rationale

TODO.md

@@ -21,6 +21,52 @@ fmt-check, and commit.
 
 # Completed Steps
 
+- 2026-11-04: Each repository now commits yarn 4 and installs with
+  `yarn install --immutable` (https://git.eeqj.de/sneak/prompts/issues/149), on
+  sneak's ruling at
+  https://git.eeqj.de/sneak/prompts/issues/149#issuecomment-167558. Product
+  repositories convert when they next have work. These changed:
+    - This repository carries `.yarn/releases/yarn-4.18.1.cjs`, and its
+      `yarn.lock` is in yarn 4's format.
+    - `script/bootstrap` no longer stops on yarn's major version.
+    - Node comes from the distribution's newest Node package, which on Alpine
+      3.24 is `nodejs-current`.
+    - A `Dockerfile` stage that needs yarn also copies `.yarnrc.yml` and
+      `.yarn/releases/`, and may start from any distribution that packages node
+      and yarn.
+    - Both checklists give the steps, and the ignore files keep yarn's install
+      state out of git and the build context.
+- 2026-11-04: An agent whose work is confined to one package may run `go test`
+  directly on that package's suite, or on individual tests in it, while
+  iterating (https://git.eeqj.de/sneak/prompts/issues/51), on sneak's ruling at
+  https://git.eeqj.de/sneak/prompts/issues/51#issuecomment-167600. The full
+  `make check` is still required before every push, and the `Makefile` gains
+  nothing. The rule on Docker now names the lint and test gates, because a run
+  while iterating is not one.
+- 2026-11-04: node, yarn, npm, python, pip and venv now come from the
+  distribution with no version and no hash
+  (https://git.eeqj.de/sneak/prompts/issues/146), on sneak's ruling at
+  https://git.eeqj.de/sneak/prompts/issues/146#issuecomment-166033. Third-party
+  packages stay pinned by hash. These changed:
+    - `script/bootstrap` no longer uses nvm or corepack, and stops when yarn's
+      major version is not 1.
+    - `script/bootstrap` installs node, yarn and the node packages only when
+      `yarn.lock` is in the tree.
+    - `script/bootstrap`, `script/fmt` and `script/fmt-check` run `yarn` or
+      `yarnpkg`, whichever is present.
+    - This repository's `Dockerfile` starts from Alpine 3.24.
+    - The Python `test` phase example starts from `debian:trixie-slim`.
+    - A Python repository's `script/bootstrap` creates its virtual environment
+      at `$HOME/.pipenv`, so it works on a host and in a `Dockerfile`.
+    - `PIP_ONLY_BINARY=:all:` stops a package with no wheel, so pip downloads no
+      build tools without a hash check.
+- 2026-11-04: Rewrote `prompts/REPO_POLICIES.md` sentence by sentence
+  (https://git.eeqj.de/sneak/prompts/issues/136), on sneak's yes at
+  https://git.eeqj.de/sneak/prompts/issues/136#issuecomment-165193. Every rule
+  keeps its meaning and its place, and `must` and `should` stay as they were.
+  Long sentences are split, comma-chained lists are now bulleted lists, and
+  every reason stays. Code blocks, digests, URLs, file names, commands and
+  quoted strings are unchanged.
 - 2026-11-03: The canonical golangci-lint is now v2.15.0, still built with
   go1.27.0, so the `go` directive rule is unchanged (issue 142). Repositories
   pick this up on their next re-vendor. Each item in the canonical

package.json

@@ -2,5 +2,6 @@
   "private": true,
   "devDependencies": {
     "prettier": "3.8.1"
-  }
+  },
+  "packageManager": "yarn@4.18.1"
 }

prompts/CODE_STYLEGUIDE_JS.md

@@ -1,6 +1,6 @@
 ---
 title: Code Styleguide — JavaScript
-last_modified: 2026-02-22
+last_modified: 2026-11-04
 ---
 
 1. Use `const` for everything. If you need to reassign, use `let`. Never use
@@ -8,7 +8,8 @@ last_modified: 2026-02-22
 
 1. Use yarn for package management, avoid using npm.
 
-1. Use LTS node versions.
+1. Install node from the distribution. If its version is too old, use a newer
+   distribution.
 
 1. Use `prettier` for code formatting, with four spaces for indentation.
 

prompts/EXISTING_REPO_CHECKLIST.md

@@ -1,6 +1,6 @@
 ---
 title: Existing Repo Checklist
-last_modified: 2026-11-03
+last_modified: 2026-11-04
 ---
 
 Use this checklist when beginning work in a repo that may not yet conform to our
@@ -56,14 +56,14 @@ with your task.
     - the step that runs `script/bootstrap` to install a Python `test` phase's
       packages from `Pipfile.lock`
 - [ ] A stage with none of these steps declares `ARG CACHEBUST` right after
-      `FROM`. A step that installs anything else as well, such as a
-      `script/bootstrap` that also installs node packages, comes after it too.
-      The `script/` builds pass a new `CACHEBUST` value on every build, which
-      reruns every `RUN` step after that line and leaves the layers above it and
-      the cache mounts in place; `--no-cache` would build those layers again and
-      empty the mounts. A stage without the `ARG` line is served from cache on
-      an unchanged tree, so the scripts and the `ARG` lines are re-vendored in
-      one commit.
+      `FROM`. A step that also installs anything else comes after
+      `ARG CACHEBUST` too. A `script/bootstrap` that also installs node packages
+      is one. The `script/` builds pass a new `CACHEBUST` value on every build,
+      which reruns every `RUN` step after that line and leaves the layers above
+      it and the cache mounts in place; `--no-cache` would build those layers
+      again and empty the mounts. A stage without the `ARG` line is served from
+      cache on an unchanged tree, so the scripts and the `ARG` lines are
+      re-vendored in one commit.
 - [ ] Go: each Go stage downloads the modules (`COPY go.mod go.sum ./`,
       `RUN go mod download`) above `ARG CACHEBUST`; the steps that compile
       (`golangci-lint run`, `go test`, `go build`) mount Go's build cache
@@ -76,15 +76,25 @@ with your task.
 - [ ] Python: a `test` phase that installs its packages from `Pipfile.lock` does
       it above `ARG CACHEBUST`, with `COPY script/ script/`,
       `COPY Pipfile Pipfile.lock ./` and `RUN script/bootstrap`. When
-      `script/bootstrap` runs in that step, it installs nothing beyond system
-      packages, pipenv and its dependencies, and the packages from
-      `Pipfile.lock`. It installs pipenv and its dependencies by hash, with
-      `pip install --require-hashes`. It installs the packages from
-      `Pipfile.lock` with `pipenv install --deploy`, plus `--dev` when the tests
-      need the development packages. It installs no Python there, because the
-      tests use the base image's. The tests run after `ARG CACHEBUST`, and every
-      other stage installs its Python packages after it, as in the Python `test`
-      phase example in `REPO_POLICIES.md`
+      `script/bootstrap` runs in that step, it installs nothing beyond these:
+    - system packages
+    - pipenv and its dependencies
+    - the packages from `Pipfile.lock`
+
+    It creates a virtual environment at `$HOME/.pipenv` with `python3 -m venv`
+    when it is missing, then uses that environment's `pip` and `pipenv`. On a
+    host, it first installs the distribution's python and venv packages when
+    they are missing. It installs pipenv and its dependencies by hash, with
+    `pip install --require-hashes`. It installs the packages from `Pipfile.lock`
+    with `pipenv install --deploy`, plus `--dev` when the tests need the
+    development packages. It sets `PIP_ONLY_BINARY=:all:` for both installs, so
+    a package with no wheel for the image stops the install. In that step it
+    installs no Python, because a step above it already did. `Pipfile` names no
+    `python_version`, because `--deploy` stops when the distribution's Python
+    differs from it. The tests run after `ARG CACHEBUST`, and every other stage
+    installs its Python packages after it, as in the Python `test` phase example
+    in `REPO_POLICIES.md`
+
 - [ ] The gate phases invoke their tools directly, never through `make lint` or
       `script/test` — those are themselves a `docker build` and would recurse
       inside a build step
@@ -105,37 +115,43 @@ with your task.
       `services/api/.claude/`: add anchored entries for those directories.
 - [ ] If the repo embeds a version in a binary: `.dockerignore` lets `.git` into
       the build context. It keeps out every git `config` at any depth
-      (`**/.git/config`, `**/.git/modules/**/config`): the repository's own,
-      each submodule's under `.git/modules/`, and that of a submodule keeping
-      its own `.git` directory. `git describe` does not need them, and each can
-      hold a credential: a password in a remote URL, or the token the CI
-      checkout step stores there. A submodule whose name has a `config` segment
-      (`config`, `deploy/config`, `config/lib`) loses its whole git directory to
-      `**/.git/modules/**/config`, and Go's version stamping then fails the
-      build: give it a name without that segment (`git submodule add --name`).
-      The stage that compiles has `git` (the Debian Go image has it; an alpine
-      one needs `apk add --no-cache git`) and takes the version from the
-      `VERSION` build argument when one is given, otherwise from
-      `git describe --tags --always`. That gives the tag on a tagged commit; on
-      a later commit, the tag, the number of commits since it and the short
-      commit (`v1.2.3-4-gabc1234`); and the short commit when no tag is
-      reachable. The stage that compiles also marks its working directory safe
-      for git (`git config --system --add safe.directory /src`): a context sent
-      as a tar stream keeps the sender's file owners, and git refuses a checkout
-      owned by another user, so the version would come out empty. `ARG VERSION`
-      has no default, and the build fails if the context carries `.git` and the
-      version still comes out empty, `dev` or `unknown`. A plain
-      `docker build .` with no build arguments must succeed; a Dockerfile that
-      refuses an empty build argument drops that refusal and keeps the argument.
-      A checkout whose `.git` is a file (a linked worktree, or a repository
-      checked out as a submodule) is the exception: that file points to a git
-      directory outside the build context, so the build cannot read the version
-      and a plain `docker build .` fails; pass the version with
-      `--build-arg VERSION=...`. `script/docker` and `script/cibuild` already
-      pass the version they compute on the host; it takes precedence. The
-      canonical `.gitea/workflows/check.yml` sets `fetch-depth: 0` on its
-      checkout step, which otherwise clones shallow and fetches no tags, so a CI
-      build finds the tag too.
+      (`**/.git/config`, `**/.git/modules/**/config`):
+    - the repository's own
+    - each submodule's under `.git/modules/`
+    - that of a submodule keeping its own `.git` directory
+
+    `git describe` does not need them, and each can hold a credential: a
+    password in a remote URL, or the token the CI checkout step stores there.
+    Some submodule names have a `config` segment, as in `config`,
+    `deploy/config` or `config/lib`. Such a submodule loses its whole git
+    directory to `**/.git/modules/**/config`, and Go's version stamping then
+    fails the build. Give it a name without that segment
+    (`git submodule add --name`). The stage that compiles has `git`: the Debian
+    Go image has it, and an alpine one needs `apk add --no-cache git`. That
+    stage takes the version from the `VERSION` build argument when one is given,
+    otherwise from `git describe --tags --always`. That gives:
+    - the tag, on a tagged commit
+    - the tag, the number of commits since it and the short commit
+      (`v1.2.3-4-gabc1234`), on a later commit
+    - the short commit, when no tag is reachable
+
+    The stage that compiles also marks its working directory safe for git
+    (`git config --system --add safe.directory /src`). A context sent as a tar
+    stream keeps the sender's file owners, and git refuses a checkout owned by
+    another user, so the version would come out empty. `ARG VERSION` has no
+    default. The build fails if the context carries `.git` and the version still
+    comes out empty, `dev` or `unknown`. A plain `docker build .` with no build
+    arguments must succeed; a Dockerfile that refuses an empty build argument
+    drops that refusal and keeps the argument. A checkout whose `.git` is a file
+    is the exception: a linked worktree, or a repository checked out as a
+    submodule. That file points to a git directory outside the build context, so
+    the build cannot read the version and a plain `docker build .` fails. Pass
+    the version with `--build-arg VERSION=...`. `script/docker` and
+    `script/cibuild` already pass the version they compute on the host; it takes
+    precedence. The canonical `.gitea/workflows/check.yml` sets `fetch-depth: 0`
+    on its checkout step, which otherwise clones shallow and fetches no tags, so
+    a CI build finds the tag too.
+
 - [ ] Gitea Actions workflow in `.gitea/workflows/` runs `script/cibuild` on
       push, checks out with `persist-credentials: false` and with
       `fetch-depth: 0` (which fetches the tags `git describe` needs), carries
@@ -148,10 +164,39 @@ with your task.
           `https://git.eeqj.de/sneak/prompts/raw/branch/main/.golangci.yml` and,
           in the same commit, set the lint phase digest to the one named in the
           `.golangci.yml` paragraph of `REPO_POLICIES.md`)
-    - [ ] JS: `package.json`, `yarn.lock`, `.prettierrc`, `.prettierignore`
-          (fetch from
-          `https://git.eeqj.de/sneak/prompts/raw/branch/main/.prettierrc` and
-          `https://git.eeqj.de/sneak/prompts/raw/branch/main/.prettierignore`)
+    - [ ] JS: `package.json`, `yarn.lock`, `.yarnrc.yml`, `.yarn/releases/`,
+          `.gitattributes`, `.prettierrc`, `.prettierignore` (fetch the last two
+          from `https://git.eeqj.de/sneak/prompts/raw/branch/main/.prettierrc`
+          and
+          `https://git.eeqj.de/sneak/prompts/raw/branch/main/.prettierignore`).
+    - [ ] Any repository with `yarn.lock`: that file is in yarn 4's format. If
+          its second line says `yarn lockfile v1`, convert it with the steps
+          below. Do them in one commit with the re-vendored scripts, because
+          yarn 1 ignores `--immutable` and exits 0 on a tree with no
+          `.yarnrc.yml`. Run them with any distribution's node and yarn, and use
+          `yarnpkg` on Debian and Ubuntu.
+        1. Read the version from `yarnPath` in
+           `https://git.eeqj.de/sneak/prompts/raw/branch/main/.yarnrc.yml`.
+        2. Run `yarn set version <version>`. It writes
+           `.yarn/releases/yarn-<version>.cjs`, `yarnPath` in `.yarnrc.yml`, and
+           `packageManager` in `package.json`.
+        3. Add `nodeLinker: node-modules` and `enableTelemetry: false` to
+           `.yarnrc.yml`.
+        4. Run `yarn install` once. It converts `yarn.lock`, and each package
+           keeps its version and gains a `checksum`.
+        5. Delete `approvedGitRepositories`, `enableScripts` and
+           `npmMinimalAgeGate` from `.yarnrc.yml`. The conversion wrote them.
+           They allow install scripts, any git repository and packages of any
+           age, which yarn otherwise refuses.
+        6. In `package.json`, name any package that must run its install script,
+           as `"dependenciesMeta": { "<name>": { "built": true } }`, and run
+           `yarn install` again.
+        7. Add `.yarn/*` and `!.yarn/releases` above the secret patterns in
+           `.gitignore` and `.dockerignore`. Docker obeys the last matching
+           line, and the secret patterns must win. Add `.yarn/` to
+           `.prettierignore`, and `.yarn/releases/** binary` to
+           `.gitattributes`.
+        8. Run `yarn install --immutable`. It must pass and change nothing.
     - [ ] Python: `pyproject.toml`
     - [ ] Docs/writing: `.prettierrc`, `.prettierignore` (same URLs as above)
 
@@ -186,13 +231,20 @@ with your task.
       `docker build` in `script/`. Without the bootstrap the CI run dies in
       `script/fmt-check`, which runs the formatter on the host and finds nothing
       installed.
-- [ ] `script/fmt` and `script/fmt-check` pick their `yarn` with the same test
-      as `script/bootstrap`: the `yarn` on `PATH` when the node on `PATH` has
-      the pinned major version, and otherwise yarn under the pinned node, with
-      nvm loaded through `$HOME/.nvm/nvm.sh`. `script/bootstrap` leaves the node
-      and yarn it installs under nvm off the `PATH` of the shell that called it,
-      so a bare `yarn` exits 127 on a runner carrying nothing but docker and
-      git, or runs under another node.
+- [ ] `script/bootstrap` installs node, yarn and the node packages only when
+      `yarn.lock` is in the tree. node and yarn come from the distribution when
+      they are missing. It installs the node packages with
+      `yarn install --immutable`. The distribution's yarn only starts the
+      release file that `yarnPath` in `.yarnrc.yml` names, and that file does
+      the work.
+- [ ] A `Dockerfile` stage that needs yarn may start from any distribution that
+      packages node and yarn. It copies `package.json`, `yarn.lock`,
+      `.yarnrc.yml` and `.yarn/releases/` before it runs `script/bootstrap`. A
+      stage that needs no yarn copies none of them.
+- [ ] `script/bootstrap`, `script/fmt` and `script/fmt-check` run yarn by
+      whichever name is present: `yarn`, or `yarnpkg` on Debian and Ubuntu. With
+      neither name on `PATH`, `script/fmt` and `script/fmt-check` print one line
+      saying to run `script/bootstrap`, and exit 1.
 - [ ] `script/bootstrap` installs no linter of its own — delete the block, its
       version variables and its call site. A JS repo's `yarn install` stays; it
       brings a linter along with every other dependency, and no verdict is taken
@@ -220,8 +272,16 @@ with your task.
       is a package from the distribution's own package index, which needs no
       version and no hash. Pulling that index is also allowed. In a
       `Dockerfile`, the distribution is the pinned base image's. On a host, it
-      is the host's. A package source that a `Dockerfile` adds itself does not
-      get this exception
+      is the host's, and the host's package manager stands for it, nix and brew
+      included. A package source that a `Dockerfile` adds itself does not get
+      this exception
+- [ ] node, yarn, npm, python, pip and venv come from the distribution wherever
+      possible, never from nvm, pyenv, corepack or `npm install -g yarn`. If the
+      distribution's version is too old, use a newer distribution. node means
+      the distribution's newest Node package, such as `nodejs-current` on Alpine
+      3.24
+- [ ] yarn's release file is in git under `.yarn/releases/`, written once by
+      `yarn set version` with an exact version (repositories with `yarn.lock`)
 - [ ] Using `yarn`, not `npm` (JS projects)
 
 # Directory Structure
@@ -250,11 +310,12 @@ with your task.
 # Final
 
 - [ ] `make check` passes
-- [ ] `script/cibuild` succeeds in a fresh clone on a host carrying what CI has
-      (the runner image `docker.gitea.com/runner-images:ubuntu-latest`: docker,
-      git and node 24, with no yarn on `PATH`), and demonstrably executed the
-      checks — a sub-second build, or `CACHED` on a step that lints or tests,
-      one of the `RUN` steps below `ARG CACHEBUST`, means nothing ran. Above
+- [ ] `script/cibuild` succeeds in a fresh clone on a host carrying what CI has.
+      That host is the runner image
+      `docker.gitea.com/runner-images:ubuntu-latest`, which has docker, git and
+      node 24. Take any yarn off `PATH` first. The run must show that the checks
+      executed. A sub-second build means nothing ran. So does `CACHED` on a step
+      that lints or tests, one of the `RUN` steps below `ARG CACHEBUST`. Above
       that line, these steps are expected to show `CACHED`:
     - the steps that install system packages
     - the steps that download Go's modules

prompts/NEW_REPO_CHECKLIST.md

@@ -1,6 +1,6 @@
 ---
 title: New Repo Checklist
-last_modified: 2026-11-03
+last_modified: 2026-11-04
 ---
 
 Use this checklist when creating a new repository from scratch. Follow the steps
@@ -75,34 +75,42 @@ Template files can be fetched from:
       anchored entry.
     - If the image embeds a version in a binary: `.dockerignore` lets `.git`
       into the build context. It keeps out every git `config` at any depth
-      (`**/.git/config`, `**/.git/modules/**/config`): the repository's own,
-      each submodule's under `.git/modules/`, and that of a submodule keeping
-      its own `.git` directory. `git describe` does not need them, and each can
-      hold a credential: a password in a remote URL, or the token the CI
-      checkout step stores there. A submodule whose name has a `config` segment
-      (`config`, `deploy/config`, `config/lib`) loses its whole git directory to
-      `**/.git/modules/**/config`, and Go's version stamping then fails the
-      build: give it a name without that segment (`git submodule add --name`).
-      The stage that compiles has `git` (the Debian Go image has it; an alpine
-      one needs `apk add --no-cache git`) and takes the version from the
-      `VERSION` build argument when one is given, otherwise from
-      `git describe --tags --always`. That gives the tag on a tagged commit; on
-      a later commit, the tag, the number of commits since it and the short
-      commit (`v1.2.3-4-gabc1234`); and the short commit when no tag is
-      reachable. The stage that compiles also marks its working directory safe
-      for git (`git config --system --add safe.directory /src`): a context sent
-      as a tar stream keeps the sender's file owners, and git refuses a checkout
-      owned by another user, so the version would come out empty. `ARG VERSION`
-      has no default, and the build fails if the context carries `.git` and the
-      version still comes out empty, `dev` or `unknown`. A plain
-      `docker build .` with no build arguments must succeed; a Dockerfile that
-      refuses an empty build argument drops that refusal and keeps the argument.
-      A checkout whose `.git` is a file (a linked worktree, or a repository
-      checked out as a submodule) is the exception: that file points to a git
-      directory outside the build context, so the build cannot read the version
-      and a plain `docker build .` fails; pass the version with
-      `--build-arg VERSION=...`, as `script/docker` and `script/cibuild` already
-      do.
+      (`**/.git/config`, `**/.git/modules/**/config`):
+        - the repository's own
+        - each submodule's under `.git/modules/`
+        - that of a submodule keeping its own `.git` directory
+
+        `git describe` does not need them, and each can hold a credential: a
+        password in a remote URL, or the token the CI checkout step stores
+        there. Some submodule names have a `config` segment, as in `config`,
+        `deploy/config` or `config/lib`. Such a submodule loses its whole git
+        directory to `**/.git/modules/**/config`, and Go's version stamping then
+        fails the build. Give it a name without that segment
+        (`git submodule add --name`). The stage that compiles has `git`: the
+        Debian Go image has it, and an alpine one needs
+        `apk add --no-cache git`. That stage takes the version from the
+        `VERSION` build argument when one is given, otherwise from
+        `git describe --tags --always`. That gives:
+        - the tag, on a tagged commit
+        - the tag, the number of commits since it and the short commit
+          (`v1.2.3-4-gabc1234`), on a later commit
+        - the short commit, when no tag is reachable
+
+        The stage that compiles also marks its working directory safe for git
+        (`git config --system --add safe.directory /src`). A context sent as a
+        tar stream keeps the sender's file owners, and git refuses a checkout
+        owned by another user, so the version would come out empty.
+        `ARG VERSION` has no default. The build fails if the context carries
+        `.git` and the version still comes out empty, `dev` or `unknown`. A
+        plain `docker build .` with no build arguments must succeed; a
+        Dockerfile that refuses an empty build argument drops that refusal and
+        keeps the argument. A checkout whose `.git` is a file is the exception:
+        a linked worktree, or a repository checked out as a submodule. That file
+        points to a git directory outside the build context, so the build cannot
+        read the version and a plain `docker build .` fails. Pass the version
+        with `--build-arg VERSION=...`, as `script/docker` and `script/cibuild`
+        already do.
+
     - The Dockerfile carries a `lint` phase and a `test` phase, each invoking
       its tool directly rather than through `make` or `script/`, and the final
       stage carries a `COPY --from=` of a harmless file from each so the image
@@ -115,14 +123,14 @@ Template files can be fetched from:
         - the step that runs `script/bootstrap` to install a Python `test`
           phase's packages from `Pipfile.lock`
     - A stage with none of these steps declares `ARG CACHEBUST` right after
-      `FROM`. A step that installs anything else as well, such as a
-      `script/bootstrap` that also installs node packages, comes after it too.
-      The `script/` builds pass a new `CACHEBUST` value on every build, which
-      reruns every `RUN` step after that line and leaves the layers above it and
-      the cache mounts in place; `--no-cache` would build those layers again and
-      empty the mounts. A stage without the `ARG` line is served from cache on
-      an unchanged tree, so the scripts and every stage's `ARG CACHEBUST` line
-      are added in the same commit.
+      `FROM`. A step that also installs anything else comes after
+      `ARG CACHEBUST` too. A `script/bootstrap` that also installs node packages
+      is one. The `script/` builds pass a new `CACHEBUST` value on every build,
+      which reruns every `RUN` step after that line and leaves the layers above
+      it and the cache mounts in place; `--no-cache` would build those layers
+      again and empty the mounts. A stage without the `ARG` line is served from
+      cache on an unchanged tree, so the scripts and every stage's
+      `ARG CACHEBUST` line are added in the same commit.
     - Go: each Go stage downloads the modules (`COPY go.mod go.sum ./`,
       `RUN go mod download`) above `ARG CACHEBUST`; the steps that compile
       (`golangci-lint run`, `go test`, `go build`) mount Go's build cache
@@ -135,18 +143,30 @@ Template files can be fetched from:
     - Python: a `test` phase that installs its packages from `Pipfile.lock` does
       it above `ARG CACHEBUST`, with `COPY script/ script/`,
       `COPY Pipfile Pipfile.lock ./` and `RUN script/bootstrap`. When
-      `script/bootstrap` runs in that step, it installs nothing beyond system
-      packages, pipenv and its dependencies, and the packages from
-      `Pipfile.lock`. It installs pipenv and its dependencies by hash, with
-      `pip install --require-hashes`. It installs the packages from
-      `Pipfile.lock` with `pipenv install --deploy`, plus `--dev` when the tests
-      need the development packages. It installs no Python there, because the
-      tests use the base image's. The tests run after `ARG CACHEBUST`, and every
-      other stage installs its Python packages after it, as in the Python `test`
-      phase example in `REPO_POLICIES.md`
+      `script/bootstrap` runs in that step, it installs nothing beyond these:
+        - system packages
+        - pipenv and its dependencies
+        - the packages from `Pipfile.lock`
+
+        It creates a virtual environment at `$HOME/.pipenv` with
+        `python3 -m venv` when it is missing, then uses that environment's `pip`
+        and `pipenv`. On a host, it first installs the distribution's python and
+        venv packages when they are missing. It installs pipenv and its
+        dependencies by hash, with `pip install --require-hashes`. It installs
+        the packages from `Pipfile.lock` with `pipenv install --deploy`, plus
+        `--dev` when the tests need the development packages. It sets
+        `PIP_ONLY_BINARY=:all:` for both installs, so a package with no wheel
+        for the image stops the install. In that step it installs no Python,
+        because a step above it already did. `Pipfile` names no
+        `python_version`, because `--deploy` stops when the distribution's
+        Python differs from it. The tests run after `ARG CACHEBUST`, and every
+        other stage installs its Python packages after it, as in the Python
+        `test` phase example in `REPO_POLICIES.md`
+
     - Server: the final stage builds and runs the application
     - Non-server: the final stage brings up the dev environment
     - Image pinned by sha256 hash with version/date comment
+
 - [ ] Gitea Actions workflow at `.gitea/workflows/check.yml` that runs
       `script/cibuild` on push, checks out with `persist-credentials: false` and
       with `fetch-depth: 0` (which fetches the tags `git describe` needs),
@@ -159,7 +179,22 @@ Template files can be fetched from:
           `https://git.eeqj.de/sneak/prompts/raw/branch/main/.golangci.yml` and,
           in the same commit, set the lint phase digest to the one named in the
           `.golangci.yml` paragraph of `REPO_POLICIES.md`)
-    - [ ] JS: `yarn init`, `yarn add --dev prettier`
+    - [ ] JS, or any repository that runs prettier through yarn: make the first
+          `yarn.lock` with the steps below. `script/bootstrap` installs no yarn
+          until `yarn.lock` exists, so run them with any distribution's node and
+          yarn, such as Alpine's (`apk add nodejs-current yarn`). Use `yarnpkg`
+          on Debian and Ubuntu.
+        1. Read the version from `yarnPath` in
+           `https://git.eeqj.de/sneak/prompts/raw/branch/main/.yarnrc.yml`.
+        2. Run `yarn set version <version>`. It writes
+           `.yarn/releases/yarn-<version>.cjs`, `.yarnrc.yml` and
+           `package.json`.
+        3. Add `nodeLinker: node-modules` and `enableTelemetry: false` to
+           `.yarnrc.yml`.
+        4. Add `"private": true` to `package.json`.
+        5. Run `yarn add --dev prettier`. It writes `yarn.lock`.
+        6. Add `.yarn/releases/** binary` to `.gitattributes`.
+        7. Run `yarn install --immutable`. It must pass and change nothing.
     - [ ] Python: `pyproject.toml`
 
 ## Configure script/ Entrypoints and Makefile
@@ -170,14 +205,23 @@ are thin shims calling them. Model scripts:
 
 - [ ] scripts are POSIX sh (`#!/bin/sh`, `set -eu`, no bashisms) so they run on
       alpine images without bash
-- [ ] `script/bootstrap` / `make bootstrap` — installs all dependencies,
-      idempotently, assuming nothing (pkg manager detection nix/apt/brew/apk;
-      node used if its major version is the pinned one, else pinned version via
-      nvm from a hash-verified archive, with yarn and the packages installed
-      under it; pinned yarn via corepack); a non-server repo's development
-      environment stage runs it instead of inline installs; a gate phase or the
-      build stage installs what its base image lacks either inline or by running
-      it
+- [ ] `script/bootstrap` / `make bootstrap` installs all dependencies,
+      idempotently, and assumes nothing is present:
+    - It detects the package manager: nix, apt, brew or apk.
+    - It installs node, yarn and the node packages only when `yarn.lock` is in
+      the tree. node and yarn come from that package manager when they are
+      missing.
+    - It installs the node packages with `yarn install --immutable`. The
+      distribution's yarn only starts the release file that `yarnPath` in
+      `.yarnrc.yml` names, and that file does the work.
+    - A non-server repo's development environment stage runs it, with only
+      system packages installed inline above it.
+    - A gate phase or the build stage installs what its base image lacks, either
+      inline or by running it.
+- [ ] A `Dockerfile` stage that needs yarn may start from any distribution that
+      packages node and yarn. It copies `package.json`, `yarn.lock`,
+      `.yarnrc.yml` and `.yarn/releases/` before it runs `script/bootstrap`. A
+      stage that needs no yarn copies none of them.
 - [ ] `script/setup` / `make setup` — readies a fresh clone: runs `bootstrap`,
       then `install-precommit`, plus repo-specific init
 - [ ] `script/test` / `make test` —
@@ -207,13 +251,10 @@ are thin shims calling them. Model scripts:
       from `script/projectname`, each assigned on its own line before the build.
       The bootstrap is required: CI checks out and runs this alone, and
       `script/fmt-check` runs the formatter on the host.
-- [ ] `script/fmt` and `script/fmt-check` pick their `yarn` with the same test
-      as `script/bootstrap`: the `yarn` on `PATH` when the node on `PATH` has
-      the pinned major version, and otherwise yarn under the pinned node, with
-      nvm loaded through `$HOME/.nvm/nvm.sh`. `script/bootstrap` leaves the node
-      and yarn it installs under nvm off the `PATH` of the shell that called it,
-      so a bare `yarn` exits 127 on a runner carrying nothing but docker and
-      git, or runs under another node.
+- [ ] `script/bootstrap`, `script/fmt` and `script/fmt-check` run yarn by
+      whichever name is present: `yarn`, or `yarnpkg` on Debian and Ubuntu. With
+      neither name on `PATH`, `script/fmt` and `script/fmt-check` print one line
+      saying to run `script/bootstrap`, and exit 1.
 - [ ] No `docker build` in `script/` leaves a dangling image behind:
       `script/lint` and `script/test` write no image, and `script/docker` and
       `script/cibuild` tag theirs
@@ -228,11 +269,12 @@ are thin shims calling them. Model scripts:
 
 - [ ] `make check` passes
 - [ ] `make docker` succeeds
-- [ ] `script/cibuild` succeeds in a fresh clone on a host carrying what CI has
-      (the runner image `docker.gitea.com/runner-images:ubuntu-latest`: docker,
-      git and node 24, with no yarn on `PATH`), and demonstrably executed the
-      checks — a sub-second build, or `CACHED` on a step that lints or tests,
-      one of the `RUN` steps below `ARG CACHEBUST`, means nothing ran. Above
+- [ ] `script/cibuild` succeeds in a fresh clone on a host carrying what CI has.
+      That host is the runner image
+      `docker.gitea.com/runner-images:ubuntu-latest`, which has docker, git and
+      node 24. Take any yarn off `PATH` first. The run must show that the checks
+      executed. A sub-second build means nothing ran. So does `CACHED` on a step
+      that lints or tests, one of the `RUN` steps below `ARG CACHEBUST`. Above
       that line, these steps are expected to show `CACHED`:
     - the steps that install system packages
     - the steps that download Go's modules
@@ -246,8 +288,16 @@ are thin shims calling them. Model scripts:
 - [ ] No mutable image/package references. The one exception is a package from
       the distribution's own package index, which needs no version and no hash.
       Pulling that index is also allowed. In a `Dockerfile`, the distribution is
-      the pinned base image's. On a host, it is the host's. A package source
+      the pinned base image's. On a host, it is the host's, and the host's
+      package manager stands for it, nix and brew included. A package source
       that a `Dockerfile` adds itself does not get this exception
+- [ ] node, yarn, npm, python, pip and venv come from the distribution wherever
+      possible, never from nvm, pyenv, corepack or `npm install -g yarn`. If the
+      distribution's version is too old, use a newer distribution. node means
+      the distribution's newest Node package, such as `nodejs-current` on Alpine
+      3.24
+- [ ] yarn's release file is in git under `.yarn/releases/`, written once by
+      `yarn set version` with an exact version (repositories with `yarn.lock`)
 - [ ] No unnecessary files in repo root
 - [ ] All dates written as YYYY-MM-DD
 

script/bootstrap

@@ -1,24 +1,17 @@
 #!/bin/sh
 # script/bootstrap: install all dependencies needed to build and develop
 # this repo. Idempotent: every install is guarded by a check so already
-# installed tools are skipped. Base tooling comes from nix, apt, brew,
-# or apk (detected in that order); assumes nothing is present. The
-# installed node is used only when its major version is the pinned one;
-# otherwise (node missing, or another major) the pinned version is
-# installed via nvm (installing nvm itself first, from a hash-verified
-# release archive, never curl | sh), and yarn and the packages are
-# installed under it.
+# installed tools are skipped. Base tools, node and yarn come from nix,
+# apt, brew, or apk (detected in that order), with no version and no
+# hash, because the distribution is trusted. It installs node, yarn and
+# the node packages only when yarn.lock is in the tree. The
+# distribution's yarn only starts the release file that yarnPath in
+# .yarnrc.yml names, and that file does the work. So git pins the yarn
+# that runs. Assumes nothing is present.
 set -eu
 
 ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
 
-# Pinned versions, 2026-07-06
-NODE_VERSION="22.17.0"
-NVM_VERSION="0.40.3"
-# sha256 of https://github.com/nvm-sh/nvm/archive/refs/tags/v0.40.3.tar.gz
-NVM_SHA256="5f4d6aaa04a177dc93c985e31dbc411ab6b8c6e1e21d8015dbc1372625fcd1d0"
-YARN_VERSION="1.22.22"
-
 PKGMGR=""
 SUDO=""
 APT_UPDATED=""
@@ -67,99 +60,33 @@ missing() {
     ! command -v "$1" >/dev/null 2>&1
 }
 
-# verify_sha256 <file> <expected-hash>
-verify_sha256() {
-    if command -v sha256sum >/dev/null 2>&1; then
-        actual="$(sha256sum "$1" | cut -d' ' -f1)"
+# Debian and Ubuntu name the yarn command yarnpkg.
+run_yarn() {
+    if command -v yarn >/dev/null 2>&1; then
+        yarn "$@"
+    elif command -v yarnpkg >/dev/null 2>&1; then
+        yarnpkg "$@"
     else
-        actual="$(shasum -a 256 "$1" | cut -d' ' -f1)"
-    fi
-    if [ "$actual" != "$2" ]; then
-        echo "bootstrap: sha256 mismatch for $1" >&2
-        echo "  expected: $2" >&2
-        echo "  actual:   $actual" >&2
+        echo "no yarn; run script/bootstrap first" >&2
         exit 1
     fi
 }
 
-# nvm is a bash script; run a command in a bash with nvm loaded
-nvm_sh() {
-    bash -c ". \"\$HOME/.nvm/nvm.sh\" && $*"
-}
-
-ensure_nvm() {
-    [ -s "$HOME/.nvm/nvm.sh" ] && return 0
-    # nvm prerequisites; nvm itself requires bash
-    if missing bash; then pkg_install bash bash bash bash; fi
-    if missing curl; then pkg_install curl curl curl curl; fi
-    if missing git; then pkg_install git git git git; fi
-    tmp="$(mktemp -d)"
-    curl -fsSL -o "$tmp/nvm.tar.gz" \
-        "https://github.com/nvm-sh/nvm/archive/refs/tags/v${NVM_VERSION}.tar.gz"
-    verify_sha256 "$tmp/nvm.tar.gz" "$NVM_SHA256"
-    mkdir -p "$HOME/.nvm"
-    tar -xzf "$tmp/nvm.tar.gz" -C "$HOME/.nvm" --strip-components=1
-    rm -rf "$tmp"
-}
-
-# True when the node on PATH has the pinned major version. Only the
-# major is compared: the Dockerfile stages start from a node 22 alpine
-# image whose exact version is not the pin, and nvm cannot install a
-# prebuilt node on alpine. Another major is not used: the pinned yarn 1
-# prints a deprecation warning under node 24. script/fmt and
-# script/fmt-check carry this function unchanged, to run the yarn
-# installed here.
-node_is_pinned_major() {
-    if ! command -v node >/dev/null 2>&1; then return 1; fi
-    installed="$(node --version)"
-    installed="${installed#v}"
-    [ "${installed%%.*}" = "${NODE_VERSION%%.*}" ]
-}
-
-ensure_node() {
-    if node_is_pinned_major; then
-        echo "bootstrap: using node $(node --version)"
-        return 0
-    fi
-    ensure_nvm
-    nvm_sh "nvm install $NODE_VERSION"
-    nvm_sh "nvm use $NODE_VERSION >/dev/null && \
-        echo \"bootstrap: using node \$(node --version)\""
-}
-
-ensure_yarn() {
-    if ! node_is_pinned_major; then
-        nvm_sh "nvm use $NODE_VERSION >/dev/null && corepack enable && \
-            corepack prepare yarn@$YARN_VERSION --activate"
-        return 0
-    fi
-    if ! missing yarn; then return 0; fi
-    if ! missing corepack; then
-        corepack enable
-        corepack prepare "yarn@$YARN_VERSION" --activate
-    else
-        npm install -g "yarn@$YARN_VERSION"
-    fi
-}
-
-install_js_deps() {
-    if node_is_pinned_major; then
-        yarn install --frozen-lockfile
-    else
-        nvm_sh "nvm use $NODE_VERSION >/dev/null && cd \"$ROOT\" && \
-            yarn install --frozen-lockfile"
-    fi
-}
-
 main() {
     cd "$ROOT"
 
     if missing make; then pkg_install gnumake make make make; fi
     if missing git; then pkg_install git git git git; fi
 
-    ensure_node
-    ensure_yarn
-    install_js_deps
+    # A Dockerfile stage that needs no yarn copies no yarn.lock.
+    if [ -f yarn.lock ]; then
+        if missing node; then pkg_install nodejs_latest nodejs node nodejs-current; fi
+        if missing yarn && missing yarnpkg; then
+            pkg_install yarn yarnpkg yarn yarn
+        fi
+
+        run_yarn install --immutable
+    fi
 
     echo "bootstrap complete"
 }

script/fmt

@@ -4,33 +4,16 @@ set -eu
 
 ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
 
-# Must match the pin in script/bootstrap.
-NODE_VERSION="22.17.0"
-
-# True when the node on PATH has the pinned major version: the same
-# function as in script/bootstrap, which uses it to decide where it
-# installs yarn.
-node_is_pinned_major() {
-    if ! command -v node >/dev/null 2>&1; then return 1; fi
-    installed="$(node --version)"
-    installed="${installed#v}"
-    [ "${installed%%.*}" = "${NODE_VERSION%%.*}" ]
-}
-
-# Run the yarn script/bootstrap installed: the yarn on PATH when the
-# node on PATH has the pinned major version, and otherwise yarn under
-# the pinned node in nvm, which bootstrap leaves off the PATH of the
-# shell that called it. nvm is a bash script, hence the subshell.
+# Debian and Ubuntu name the yarn command yarnpkg.
 run_yarn() {
-    if node_is_pinned_major && command -v yarn >/dev/null 2>&1; then
-        exec yarn "$@"
-    fi
-    if node_is_pinned_major || [ ! -s "$HOME/.nvm/nvm.sh" ]; then
-        echo "fmt: no yarn; run script/bootstrap first" >&2
+    if command -v yarn >/dev/null 2>&1; then
+        yarn "$@"
+    elif command -v yarnpkg >/dev/null 2>&1; then
+        yarnpkg "$@"
+    else
+        echo "no yarn; run script/bootstrap first" >&2
         exit 1
     fi
-    exec bash -c '. "$HOME/.nvm/nvm.sh" && nvm use "$1" >/dev/null &&
-        shift && exec yarn "$@"' bash "$NODE_VERSION" "$@"
 }
 
 main() {

script/fmt-check

@@ -4,33 +4,16 @@ set -eu
 
 ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
 
-# Must match the pin in script/bootstrap.
-NODE_VERSION="22.17.0"
-
-# True when the node on PATH has the pinned major version: the same
-# function as in script/bootstrap, which uses it to decide where it
-# installs yarn.
-node_is_pinned_major() {
-    if ! command -v node >/dev/null 2>&1; then return 1; fi
-    installed="$(node --version)"
-    installed="${installed#v}"
-    [ "${installed%%.*}" = "${NODE_VERSION%%.*}" ]
-}
-
-# Run the yarn script/bootstrap installed: the yarn on PATH when the
-# node on PATH has the pinned major version, and otherwise yarn under
-# the pinned node in nvm, which bootstrap leaves off the PATH of the
-# shell that called it. nvm is a bash script, hence the subshell.
+# Debian and Ubuntu name the yarn command yarnpkg.
 run_yarn() {
-    if node_is_pinned_major && command -v yarn >/dev/null 2>&1; then
-        exec yarn "$@"
-    fi
-    if node_is_pinned_major || [ ! -s "$HOME/.nvm/nvm.sh" ]; then
-        echo "fmt-check: no yarn; run script/bootstrap first" >&2
+    if command -v yarn >/dev/null 2>&1; then
+        yarn "$@"
+    elif command -v yarnpkg >/dev/null 2>&1; then
+        yarnpkg "$@"
+    else
+        echo "no yarn; run script/bootstrap first" >&2
         exit 1
     fi
-    exec bash -c '. "$HOME/.nvm/nvm.sh" && nvm use "$1" >/dev/null &&
-        shift && exec yarn "$@"' bash "$NODE_VERSION" "$@"
 }
 
 main() {

yarn.lock

@@ -1,8 +1,23 @@
-# THIS IS AN AUTOGENERATED FILE. DO NOT EDIT THIS FILE DIRECTLY.
-# yarn lockfile v1
+# This file is generated by running "yarn install" inside your project.
+# Manual changes might be lost - proceed with caution!
 
+__metadata:
+  version: 10
+  cacheKey: 10c0
 
-prettier@3.8.1:
-  version "3.8.1"
-  resolved "https://registry.yarnpkg.com/prettier/-/prettier-3.8.1.tgz#edf48977cf991558f4fcbd8a3ba6015ba2a3a173"
-  integrity sha512-UOnG6LftzbdaHZcKoPFtOcCKztrQ57WkHDeRD9t/PTQtmT0NHSeWWepj6pS0z/N7+08BHFDQVUrfmfMRcZwbMg==
+"prettier@npm:3.8.1":
+  version: 3.8.1
+  resolution: "prettier@npm:3.8.1"
+  bin:
+    prettier: bin/prettier.cjs
+  checksum: 10c0/33169b594009e48f570471271be7eac7cdcf88a209eed39ac3b8d6d78984039bfa9132f82b7e6ba3b06711f3bfe0222a62a1bfb87c43f50c25a83df1b78a2c42
+  languageName: node
+  linkType: hard
+
+"root-workspace-0b6124@workspace:.":
+  version: 0.0.0-use.local
+  resolution: "root-workspace-0b6124@workspace:."
+  dependencies:
+    prettier: "npm:3.8.1"
+  languageName: unknown
+  linkType: soft