Set up mise for toolchain management

.devcontainer/Dockerfile

@@ -1,3 +1,13 @@
-FROM mcr.microsoft.com/devcontainers/javascript-node:24
+FROM mcr.microsoft.com/devcontainers/base:ubuntu
 
-RUN npm install -g pnpm
+# Install mise for toolchain management (node, pnpm, etc.)
+RUN curl https://mise.run | MISE_INSTALL_PATH=/usr/local/bin/mise sh \
+  && echo 'eval "$(/usr/local/bin/mise activate bash)"' >> /home/vscode/.bashrc \
+  && echo 'eval "$(/usr/local/bin/mise activate zsh)"' >> /home/vscode/.zshrc
+
+# Pre-install all toolchain versions pinned in mise.toml/mise.lock into the image
+COPY mise.toml mise.lock /tmp/mise-setup/
+RUN chown -R vscode:vscode /tmp/mise-setup
+USER vscode
+RUN cd /tmp/mise-setup && mise trust && mise install
+USER root

.devcontainer/devcontainer.json

@@ -1,8 +1,10 @@
 {
   "name": "Standard",
   "build": {
-    "dockerfile": "Dockerfile"
+    "dockerfile": "Dockerfile",
+    "context": ".."
   },
+  "postCreateCommand": "mise trust && pnpm install",
   "customizations": {
     // Configure properties specific to VS Code.
     "vscode": {

CONTRIBUTING.md

@@ -4,13 +4,37 @@ This section goes over the setup of the repo for development.
 
 ## Repo setup
 
-- Install [Node.js](https://nodejs.org/) 24 LTS
-- Install [pnpm](https://pnpm.io/)
+You need [Node.js](https://nodejs.org/) and [pnpm](https://pnpm.io/). Pick
+whichever of the following options you prefer to install them.
+
+### Option 1: Use mise (recommended)
+
+[mise](https://mise.jdx.dev/getting-started.html) installs the repository's
+development tools consistently across platforms. Install mise and
+[activate it for your shell](https://mise.jdx.dev/getting-started.html#activate-mise),
+then, from the repository root, run:
+
+```bash
+mise install
+```
+
+This installs the exact tool versions recorded in `mise.toml` and `mise.lock`
+(Node.js and pnpm).
+
+### Option 2: Install the tools yourself
+
+If you prefer to manage tools yourself (or use another version manager), just
+install [Node.js](https://nodejs.org/). We support all active
+[Node.js LTS](https://nodejs.org/en/about/previous-releases) versions, so any of
+them works. pnpm self-manages its version from the `packageManager` field in
+`package.json`, so you only need to install pnpm itself:
 
 ```bash
 npm install -g pnpm
 ```
 
+### Install and build
+
 - Install dependencies
 
 ```bash

mise.toml

@@ -0,0 +1,5 @@
+[tools]
+node = "26"
+
+[settings]
+idiomatic_version_file_enable_tools = ["pnpm"]