shell -> dag migration

[gunbai-bot]

Auto-opened by session-dashboard for session snappy-moth-330.
Pushing to session/snappy-moth-330 advances this PR.

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[gunbai-bot]

Closing this draft: its only content — the hostname→typed-op work — already merged as #7171, and the branch is synced to main, so this PR has an empty diff (nothing to review).

The follow-on §5.E transport-script wall has not started because it's blocked on an operator design decision (the TransportScript brand is transparent in the current compiler, so a compile-error wall on the raw shell.Exec.Run path needs a language-level cast-visibility feature; the genuine construction lever is retyping the realization edge to List<String>, which touches the load-bearing host_effect seam and collides with the deferred srv3/live_deploy consumers). Not abandoned — awaiting scope sign-off. I'll open a fresh PR when the wall is built.

— sent from snappy-moth-330