M4.77: DXF export (R12 to 2018) with DXF Options; DWG and PICT say what to use instead

New crates/cad (L3): a hand-written ASCII DXF writer. Layers become DXF
layers (hidden: off, locked, non-printing: not plotted), straight paths
LWPOLYLINE (POLYLINE before R14), curves cubic SPLINEs through every
anchor, fills solid HATCHes (outlines in R12), strokes lines with a
lineweight and a linetype per dash pattern, type TEXT or glyph outlines,
placed images IMAGE entities linked to PNG or JPEG files. Units and
scale ($INSUNITS), scaled lineweights, 8/16/256 indexed or true colour
(420), transparency (440), Preserve Appearance / Maximize Editability,
Alter Paths for Appearance, Outline Text.

document.export {format: dxf} and document.exportDxf; useArtboards
writes one drawing per artboard; selectedOnly (any export) writes the
selection in its layers. Export As lists DXF (then DXF Options,
ui.dxfOptionsDialog for agents, remembered between exports) and DWG
greyed out; document.formats lists DWG and PICT as unsupported with a
hint, and exporting or opening them answers with it.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/control-protocol.md

@@ -295,3 +295,12 @@ system file manager (desktop only; answers `{path}`), and `file.newFromTemplate`
 in the Templates folder (preference `templatesFolder`). Older native files open as "<name> [Converted]" (preference
 `appendConverted`), so their Save asks for a new `.vectorcraft` name. Native files reopen at the view they were saved
 with.
+
+DXF Options: Export As… with the DXF format (`file.exportAs {format: "dxf"}`, then the save dialog), or
+`ui.dxfOptionsDialog {path?, …document.exportDxf options}` for agents, opens the `dxfOptions` dialog. Its fields are
+`document.export` params: `version`, `unit` (a unit name such as `Millimeters`), `scale`, `scaleLineweights`, `colors`
+(`8`, `16`, `256`, `true`), `rasterFormat` (`png`, `jpeg`), `preserve` (`appearance`, `editability`), `selectedOnly`,
+`alterPaths`, `outlineText`, plus `path` and the artboard choice. `ui.dialog.confirm` checks them (a bad value, or
+Export Selected Art Only with nothing selected, keeps the dialog open), remembers them for the next DXF Options and
+writes the file (asking for a path when there is none). Export As also lists DWG, greyed out: setting its `format` to
+`dwg` shows, and on confirm answers, the hint to export DXF instead.