The success fixture can run under either tsx hook, so its previous output
assertions stayed green when runLoaderSmoke stopped forwarding sourceImport.
Line coverage therefore did not protect the supported ESM-only launcher.
Include the actual child process execArgv in the fixture output and assert
the resolved tsx/esm hook requested by the caller. The regression observes
Node launch arguments rather than reproducing the helper implementation.
Align the optional sourceImport spread with the adjacent mode spread;
this keeps the same behavior for defined and absent values.
Negative control: removing forwarding passed the old test but failed the
new assertion because the child loaded tsx/dist/loader.mjs instead of
esm/index.mjs. With forwarding restored, all 25 loader-smoke tests pass
and src/index.ts retains 100% statement, branch, function, and line coverage.
Scoped lint passes.
Tianyi Cui
8b5a78e9ac