feat: graduate the linked install strategy from experimental to stable

[manzoorwanijk]

Removes the experimental designation from install-strategy=linked (isolated mode): drops the install-time warning and the (experimental) note in the config docs. linked is now a supported, opt-in install strategy. The default stays hoisted.

Why

install-strategy=linked (RFC-0042) has been experimental since it shipped, warning on every install. It has since been hardened extensively — the discrepancies tracked in #9608, plus ~50 earlier PRs, are resolved — and it now produces hoisted-equivalent results across install/ci/ls/query/explain/audit/sbom/exec/run/link/uninstall, the supply-chain controls (allow-scripts/allow-remote/allow-git, --strict-allow-scripts), and the v12 features (npm patch, packageExtensions, .npm-extension), with a project lockfile identical to hoisted. It has also been exercised against the Gutenberg monorepo, which powers the WordPress Block Editor. The experimental warning no longer reflects its state.

How

• @npmcli/arborist (reify.js): remove the The "linked" install strategy is EXPERIMENTAL and may contain bugs. warning emitted on every linked install.
• @npmcli/config (definitions.js): drop (experimental) from the install-strategy description for linked.
• Regenerate the config docs snapshot to match.

The node_modules/.store/ layout remains an internal implementation detail. This does not change the default install strategy.

References

• Hardening tracked in [Tracking] install-strategy=linked (isolated mode) bugs #9608
• RFC-0042 (isolated mode): https://github.com/npm/rfcs/blob/main/accepted/0042-isolated-mode.md

[manzoorwanijk]

@owlstronaut the feature is no different in v11, should this be backported?

[github-actions]

🎉 Backport to release/v11 created: #9677