Extend deferred dispatch's destination pin to ordinary CLI fallback, so
custom-root and active-profile changes cannot redirect a checked target.
Refuse a missing destination before launch and name the target on failure.
Replace the old env-clearing expectation with two behavioral invariants
and retain the native Electron custom-root reproduction.
Adapted from the root-boundary fix and diagnosis in #104066.
Related #104055, #104066.
Co-authored-by: fangliquanflq <fangliquan@qq.com>