A save records the entered model viewport (or the sheet) as the layout's
last active viewport, and opening the layout enters it again with its
UCS. Picks up the codec fix that kept a last-active link from being read
as the sheet viewport (codec d57097c, kernel b40fa59, graph 2360341).
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Saving from a non-first paper layout still reopened on the first paper
tab: set_saved_active_layout only updated an existing CTAB entry, but
documents authored here never carried one, so CTAB was never written and
the reader fell back to $TILEMODE (which only records model-vs-paper) →
the first paper layout.
set_saved_active_layout now creates the CTAB DICTIONARYVAR under the root
named-object dictionary when it is absent (updating in place otherwise).
The root dictionary is taken from the header handle, or found by scanning
for the dictionary that holds ACAD_LAYOUT when a from-scratch document
has not populated the header handle yet. The writers persist it (they
serialize the document's objects and root-dictionary entries; the
root-dict rebuild in CadDocument::build() is not run on save).
Adds tests/active_space_roundtrip.rs, including a full DXF save→reload
round-trip asserting both $TILEMODE and CTAB survive.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
