`prepareDevelopmentProject()` resolved the build target from the host
platform and architecture, so a Linux host threw `unsupported target
linux-x64` while writing the runtime descriptor. Pass the target in
instead: the launcher supplies the target it prepared, and isolated tests
supply a fixed supported target.
Extract `desktopTargetPlatform()` into desktop-build-paths.mjs so the
target-to-payload mapping has one home, and use it for the qualification
runner, which previously derived both its target directory and its
descriptor from the host architecture.
Correct the README limitation to name the module that now performs the
architecture check.
- main-startup: assert primaryRuntime for the unpackaged Host and cover a
missing DSH_DESKTOP_PRIMARY_RUNTIME_DIR as a fatal startup dialog with no
Host started.
- test-workspace-updates: pass the prepared primary-runtime directory instead
of an application/runtime path the runner never creates.
- development-project: derive the descriptor platform/arch from
resolveDesktopBuildTarget so it matches the prepared payload.
- main: resolve the unpackaged primary runtime once at startup instead of
inside the Host factory.
- dev: keep the environment override symmetric with its neighbours.
- README: document the variable as required for unpackaged launches and record
the remaining win32-arm64 payload architecture limitation.
mektpoy