REFCLOSE only wrote the temp copies made at REFEDIT entry back into
the block, so anything drawn (or pasted / offset) during the session
stayed behind in model space (#423). The session now captures a
handle watermark at entry; on close, every current-space entity
allocated at or above it joins the working set — Save folds it into
the block through the same inverse transform, Discard removes it.
Covers every creation path with no per-command hooks.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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