Support platform-specific package builds (or a one-time post-install hook)

[Bombardier-C-Kram]

Background

When building a Tatin package that ships native libraries (e.g. raylibAPL), each target platform can sometimes need its own shared objects / DLLs.
Today a package author has only two (not necessarily satisfactory) choices:

1. Bundle the binaries for every supported platform inside the same package. This results in a much larger package and forces every user to download artefacts they will never use.

2. Defer the download of the correct binaries until the first LoadPackage at run time, using ⎕LX as a workaround. The hook is executed on every load, not once after install. Complicates user code and could noticeably slow down package start-up.

Request

Add first-class support for platform specificity at the package-manager level.

Possible directions (either one of these would help):

A. Multiple platform-tagged builds under the same semantic version

• e.g.
  raylibAPL-1.2.3-win64
  raylibAPL-1.2.3-linux64
  raylibAPL-1.2.3-macos
• The package manager chooses the build whose tag matches the platform.

B. A one-time post-install hook defined in apl-package.json

• Runs immediately after the package has been unpacked.
• Guarantees to run only once per install/upgrade, not on every load.
• Could be used to download or build native artefacts dynamically.

Work-around today

Use a ⎕LX expression that

1. Detects the host platform,
2. Downloads / extracts the correct library if it is missing,
   This works but is executed on every package load, which may not be needed, or wanted.