[SaKaNa-Y]

Summary

A library sets pack.envFile and pack.envPrefix: ['CUSTOM_'] to embed custom build values. Running vp pack without --env-prefix ignores that prefix and uses VITE_PACK_ and TSDOWN_ instead. The build succeeds, but custom values remain unresolved and excluded default-prefixed values enter the bundle.

Apply defaults after merging CLI options with each pack configuration:

explicit --env-prefix
  > each pack configuration's envPrefix
  > ['VITE_PACK_', 'TSDOWN_']

This preserves empty arrays and distinct prefixes across multiple pack configurations.

Evidence

• Before: The consumer assertion expects the custom value, but receives unresolved custom values and embedded default-prefixed values.
  After: The same assertion passes.
• Six regression snapshots pass across local and global CLI entrypoints. They cover string/array prefixes, empty arrays, per-configuration prefixes, exclusions, explicit overrides, and no-config defaults.
• Full validation remains incomplete. Snapshots used an existing compiled runner with freshly bundled CLI JavaScript. A local Cargo configuration mismatch blocks the complete build and a fresh runner build. vp check and unit tests still report missing generated artifacts; the unit suite also reports a core build-artifact snapshot mismatch.

Merge Danger

Door: Two-way

The change can be reverted without a migration.

Blast Radius: Pack

Builds with a configured pack.envPrefix now use that filter when no CLI override is supplied. These builds can produce different output because the configured variables replace the previously selected default-prefixed variables.

[SaKaNa-Y]

When users set pack.envPrefix, vp pack incorrectly uses the default prefixes instead. This PR fixes that behavior.

As a separate improvement, can we warn users when they explicitly configure non-empty prefixes but none match any environment variables? This can help users spot spelling mistakes or missing environment variables. An empty result can also be intentional, so the warning can leave the build running.