Evaluate environment variables in the local plugin path

[adamjreed]

Summary

Fixes #2638

See issue for description of the problem. This PR is just a one-line change to evaluate current environment variables as devbox assembles the path for local plugins. This will allow things like a dynamic root directory for plugin source.

How was it tested?

Built devbox locally with code change and copied it to /usr/local/bin/devbox. Refreshed global environment and plugins defined with an environment variable in the path now resolve properly.

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[Copilot]

Pull Request Overview

This PR enables evaluation of environment variables in the local plugin path, allowing dynamic root directories for plugin sources.

• Uses os.ExpandEnv to expand environment variables in LocalPlugin.Path()
• No other functional changes

Comments suppressed due to low confidence (2)

internal/plugin/local.go:58

• Add unit tests for LocalPlugin.Path() to verify that environment variables in ref.Path are correctly expanded.

	path := os.ExpandEnv(l.ref.Path)

internal/plugin/local.go:57

• [nitpick] Update or add a doc comment for Path() to indicate that it now expands environment variables in the provided path.

func (l *LocalPlugin) Path() string {

[Lagoja]

Looks pretty straightforward to me. @mikeland73 any pitfalls you see with this?

[mikeland73]

LGTM

[mikeland73]

This is good. Only caveat is that environment variables defined in devbox.json or passed via -e won't be available. That's probably OK?

Another approach could be to do the expansion before determining plugin type (i.e. local, remote, etc). That way we could do something like:

"includes": "${GOPLUGIN:-github:jetify-com/devbox-plugins?dir=go-monorepo}"

which would make it nicer to develop remote plugins (currently at Jetify we use this go plugin in a private repo and it's a bit annoying to test plugin updates)

Anyway let's not let perfect be enemy of good, will merge this. We can improve in follow ups.