Add support for configuring npm version in Node devcontainers

[sireeshajonnalagadda]

Context:
When using the Node feature in devcontainers, npm is installed globally but always defaults to the bundled version. This often leads to noisy update prompts when running npm commands, and any manual updates are lost after rebuilding the container.

Problem:

Developers frequently need to pin a specific npm version globally.

Current workaround requires adding an onCreateCommand in devcontainer.json to run npm install -g npm@.

This is repetitive and not baked into the image.

Solution (Implemented in this PR):

Added support for specifying npmVersion alongside version in the Node feature configuration.

Example usage:

json
"ghcr.io/devcontainers/features/node:1": {
"version": "24",
"npmVersion": "11.11.1"
}
Ensures npm version is installed globally during container build, avoiding update prompts and rebuild inconsistencies.

Changes made:

• Adds a new npmVersion option to the Node devcontainer feature so users can pin npm (or set it to latest / none) directly in devcontainer.json.

• Updates the Node feature install script to install/upgrade npm globally during build, including skip logic (none), retries, proxy handling, and a compatibility fallback when the requested npm version doesn’t match the Node version.

• Adds/updates tests and scenarios to cover installing a specific npm version, skipping npm updates, upgrading to latest, and an incompatible “latest npm + Node 16” case.

Outcome:
Developers can now configure both Node and npm versions directly in their devcontainer setup, improving reproducibility and reducing noise from npm update prompts.

[Copilot]

Pull request overview

Adds an npmVersion configuration option to the Node devcontainer feature so users can pin/upgrade (or skip updating) the globally available npm version during image build, and adds scenario coverage for the new behavior.

Changes:

• Introduces npmVersion option in the Node feature metadata.
• Updates the Node feature install script to optionally install/upgrade npm with compatibility fallback and retries.
• Adds new test scenarios/scripts for specific npm, latest npm, skipping npm updates, and an incompatibility case.

Show a summary per file

File	Description
test/node/scenarios.json	Adds new scenarios to exercise npmVersion behaviors.
test/node/install_specific_npm_version.sh	Verifies pinning npm to a specific version.
test/node/install_npm_none.sh	Adds a “skip npm update” scenario (currently minimal assertion).
test/node/install_npm_latest.sh	Verifies upgrading npm when npmVersion=latest (and pnpm still works).
test/node/install_npm_latest_incompatible.sh	Adds an incompatibility scenario (currently missing an active assertion).
src/node/install.sh	Implements npm install/upgrade logic, compatibility checks, and retries.
src/node/devcontainer-feature.json	Adds the npmVersion option and proposals/default.

Copilot's findings

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• Files reviewed: 7/7 changed files
• Comments generated: 6