Three header-only-write / half-write classes in drawing_properties_set:
1. Measured: ezdxf emits $CUSTOMPROPERTYTAG / $CUSTOMPROPERTY only after
$LASTSAVEDBY, which does not exist before R2004, so on an R12 (AC1009) or
R2000 (AC1015) document the write reported ok, drawing_properties_get
echoed it from memory, and drawing_save_as (version kept) wrote nothing --
the class f3ff703 removed for CANNOSCALE. The headless engine now refuses
with a ValueError naming the DXF version and "save as R2004 or newer",
before custom_vars is touched; the dwgprops capability reason no longer
claims custom_properties_supported unconditionally.
2. A line break in a custom key or value passed validation, ezdxf wrote it
unescaped, and the saved DXF failed to reopen (DXFStructureError) -- the
whole drawing lost, reported as success. Refused by name in the shared
validator.
3. Measured on AutoCAD 2026: AddCustomInfo rejects keys with leading/trailing
whitespace and keys containing '=', ';' or a no-break space as 'Invalid
key' -- mid-write, after the summary and earlier keys were applied, as an
unnamed COM error -- while the headless engine wrote them. The shared
validator now mirrors those rules, so both engines refuse before writing
(internal spaces, tabs, unicode and 300-char keys stay accepted, as
AutoCAD accepts them).
Pinned by save+reopen tests on R12/R2000 (refused, file reads back empty),
R2004 (round-trips), the newline case (refused, the file still opens), and
the fake-SummaryInfo COM test (no ActiveX call reaches SummaryInfo).
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FKFStjEFzpGyLq5bMpWxTd
