Reduce duplicate dependency installation across local worktrees

[nighca]

Background

When using AI-assisted development, we often create more than one local worktree to improve parallel development efficiency. In that setup, each worktree ends up reinstalling the same dependencies, including node_modules and additional assets such as SPX- and SPXLS-related WASM files. This leads to repeated installation work and unnecessary disk usage.

We need a solution that allows different worktrees to reuse dependencies as much as possible, or at least reuse them efficiently at the disk level.

What this issue is about

Explore and implement a dependency management strategy that reduces duplicated installation cost across multiple local worktrees in the Builder development workflow. The solution should consider both package-manager-managed dependencies and extra installed artifacts such as SPX-related WASM assets.

Plan

• Review the current local installation flow for Builder worktrees, including node_modules and extra installed assets such as SPX and SPXLS WASM files.
• Evaluate candidate approaches for reuse across worktrees, including switching from npm to pnpm or adopting another shared-storage strategy.
• Check whether the chosen approach can also cover non-package.json artifacts, or define an additional mechanism for those assets.
• Propose or implement a workflow that reduces repeated installs and disk duplication for multi-worktree development.

Notes

• Switching from npm to pnpm is one possible direction, but it may only solve dependencies declared in package.json.
• The final solution should also consider assets installed outside the package manager flow, especially SPX-related WASM files.
• The goal is both faster setup for additional worktrees and better disk reuse.