A non-member path package's `.workspace = true` becomes a version dependency with an empty version

[speak-agent]

Observed

A path package that is not a workspace member cannot resolve .workspace = true. A library of build logic that the members' build programs import is such a package; GalTranslPP's gpp.build is one.

# root
[workspace]
members = ["app", "tool"]
[workspace.dependencies]
mcpp.plugins = { path = "…" }

# buildlib/mcpp.toml, reached from app as { path = "../buildlib", host-module = true }
[build-dependencies]
mcpp.plugins = { workspace = true, features = ["rules-qt"], host-module = true }

warning: 'mcpp.plugins' is declared as a path dep (by 'app (build-dep)', …) and as a version dep (by 'ws.buildlib@path (build-dep)', ); the root's declaration wins.

The entry is read as a version dependency whose version is empty. It is neither inherited nor refused.

Making the package a member resolves the entry. It also makes mcpp build at the root build the package as a target, and a module-only package whose module imports a host module fails there:

   Workspace building member 'buildlib'
mcpp.rules.qt: error: failed to read compiled module: No such file or directory

Consequently the plugin version has to be written twice: once in [workspace.dependencies] and once in the helper.

Request

Either a path package inside the workspace's tree resolves .workspace = true against that workspace, or the entry is refused with a message that names the reason. An empty version should not be accepted silently.