Tonight's launch died on the Missing File modal, so the references got counted
properly: 294 missing sources, 270 of them alive on the Freebox mirror (53G, no
file under 1MB), and 24 that exist nowhere — all of Take101, 12 orbits x L/R,
already written off in 041 as "tests at best".

The plan promotes the drop-missing-sources doctrine from a one-off repair to a
standing invariant: the session holds tracks, routing and levels, and zero audio
sources at rest. Structure comes from a template (correct by construction, rather
than mutating a session back to empty and having to be right about what to
remove); state is kept by an idempotent sweep that runs at LAUNCH as well as
close, because a close-only hook is bound to the least reliable moment there is
and a crashed gig would either strand stems or eat them.

Also names the tension it has to live with: the tool refuses to drop a reference
whose audio survives elsewhere, which is exactly the state deliberate archival
creates. --allow-archived is the answer, and the rule is that only a caller which
has itself verified the copy may pass it. A human running it blind stays refused.

And a correction 043 could not have known it needed: the one-liner recorded there
now refuses, because the eleven other takes moved to the mirror after it was
written. The doc was right when written and wrong now — drift a plan should catch
instead of a gig.