Detach managed sessions when native mobile windows are discarded, retain
live reopen references, and fence ordinary startup commands by input and
session generation. Handle noexec helpers, isolate tmux discovery locale,
and count only verified live contexts against the journal limit.
Move actual shell execution coverage into the hostless framework suite.
Validation: 76 focused macOS tests passed; iOS multiplexer regressions
passed with the inherited hosted-test artwork failure still present.
