Four review findings against the COM styles block, all measured on AutoCAD 2026
(scratch documents from Documents.Add, closed without saving):
1. textstyle_create: `TextStyle.fontFile = "arial.ttf"` raises 'Filer error' for
every bare TrueType name (bundled presets included) after TextStyles.Add has
run, leaving a stub with an empty font that a retry meets as "already exists";
a full path is accepted but the STYLE record then carries the machine path.
`SetFont("Arial", bold, italic, 0, 0)` — the STYLE dialog's own route — stores
the clean `arial.ttf`. The font is now located before Add (`_com_locate_font`:
support path, then the Windows font folders), a TrueType is written by the
family/subfamily read from its `name` table (`_truetype_face`), an SHX by the
name given, an unlocatable file is refused with nothing written, and a write
ActiveX still refuses after Add deletes the entry it added.
2. _ensure_com_textstyle goes through the same helper, so DIMTXSTY / text_style
ARIAL and ISOCPEUR are created on the first call with a real font instead of
failing once and then silently binding a fontless style.
3. dimstyle_create / dimstyle_modify check a user DIMBLK/DIMBLK1/DIMBLK2 against
doc.Blocks before any write (`_com_require_arrowhead_blocks`, the headless
`_require_arrowhead_blocks` twin, same message and table-spelling rewrite);
a write that fails after DimStyles.Add restores the previous ActiveDimStyle
(discarding the unsaved overrides) and deletes the half-made style and any
preset text style the call created.
4. _com_dimensions_using un-narrows each `Layouts.Item(i).Block.Item(p)` —
declared IAcadEntity*, so `.StyleName` raised AttributeError under a makepy
cache and the blanket except reported `[]` — and swallows nothing.
The fake in tests/test_styles.py now models the measured ActiveX rules (bare
TrueType fontFile refused, SetFont by installed typeface, SetVariable refusing an
unknown arrowhead, IAcadEntity narrowing on block items, Delete) so the old code
cannot pass; nine tests cover the four findings. SECTION 18 docstrings state the
live engine's refusal rule for fonts and the pre-write arrowhead check.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FKFStjEFzpGyLq5bMpWxTd
