A program cannot ship another package's executable built for its target; the tool edge builds it for the host #711

Observed

A program's release layout may need to carry an executable that another package in the graph builds. GalTranslPP's GUI ships Updater.exe, which its workspace member Updater builds. The manifest cannot express "this dependency's executable, built for my target". The only edge that exposes another package's executable is a tool edge, used as tools = ["Updater"] with mcpp::dep_bin("gpp.updater", "Updater"), and that edge means a program for the build machine:

• The executable is built for the host (sub.target_triple = "", src/build/prepare.cppm near line 10383). A cross build would therefore ship an executable for the wrong architecture.
• It is built a second time, with a fixed release profile and its own toolchain (A host tool's sub-build resolves its own toolchain, not the one its key records, so a workspace pinned to one LLVM installs a second #710), although the workspace already builds the same member for the target.
• emit build-database builds it in full (emit build-database builds host tools in full, so planning can cost a whole build of a tool package #707).

Request

A target artifact dependency: an edge that builds a dependency's bin target for the consumer's target and profile, and exposes the resulting path to the consumer's build program. Deploy and mcpp pack should also be able to use that path. Cargo's artifact dependencies (RFC 3028) are prior art.