Save and Export ask before replacing a file that an added extension names

After the desktop save panel closes, the app adds the file type's
extension to a name typed without it (or with one the save does not
write). The panel asked only about the name as typed, so on Linux
typing `card` with `card.vectorcraft` in the folder wrote over
`card.vectorcraft` without a question. On Linux the save panel is the
XDG desktop portal, and its GTK and GNOME file choosers return the
name as typed. Windows and macOS add the extension themselves only
when the panel lists file types, and the panels of Document Info's
Save, the presets dialogs' Export…, the CSS Properties export, the
swatch and graphic style library saves and the Libraries panel's
export list none.

When the added extension names a file that exists, Save, Save As, Save
a Copy, Save as Template, the exports and the other writes through a
save panel now ask "“card.vectorcraft” already exists. Replace it?"
first (dialog `replaceFile`). OK runs the write again with the same
answer and replaces the file. Cancel writes nothing and shows the
dialog it was asked over again. The host reports whether a file exists
through a new `Services::exists`.

Docs: docs/control-protocol.md, docs/target-app-parity.md.

docs/control-protocol.md

@@ -109,7 +109,7 @@ the two can still win that race.
 | `app.export` with `useArtboards` | `{path, useArtboards: true, range? \| artboards?, …}` | Export As: PNG, JPEG and WebP write one file per chosen artboard (default all; SVG does so for a `range`), `<path stem>-<artboard>.<ext>`, and return `{path, files: [path…]}`; a PDF keeps them as pages of `path`. `useArtboards: false` covers the bounds of the visible art. The menu's Export As… is `file.exportAs`: the `exportAs` dialog (`format`, `useArtboards`, `all`, `range`), then a save dialog and the format's options: `pngOptions` / `jpgOptions` / `webpOptions`, `svgOptions`, or `savePdf` for a PDF with Use Artboards |
 | `ui.dialog.*` on `gradientStop` | `{field: "color" \| "opacity" \| "location", value}` | double-clicking a stop on the Gradient tool's annotator opens its popover (fields `index`, `x`, `y`, `tab`); set `color` (hex), `opacity` or `location` (percentages) and `ui.dialog.confirm` to apply them to the selected stop. `gradient.selectStop {index}` picks the stop the annotator, the panels and Delete/←/→ (`ui.key`) act on |
 | `engine.execute` `ui.savePdfDialog` | `{path?, preset?, range?, …document.exportPdf options}` | opens the Save PDF dialog (`file.export.pdf` with no params opens it too). Its fields are the `document.exportPdf` options: set `compatibility` with `ui.dialog.set {field: "compatibility", value: "1.5"}`, a whole section with `{field: "compression", value: {…}}`, the artboards with `__allArtboards: false` and `range`, the visible section with `__section` (General, Compression, Marks and Bleeds, Output, Advanced, Security, Summary). `ui.dialog.confirm` writes `path` (else asks for one), returns `{path, bytes, warnings}` and opens the file when `viewAfterSaving` is set |
-| `file.save` / `file.saveAs` / `file.saveCopy` / `file.saveAsTemplate` (via `engine.execute`) | `{path?, format?, options?, svg?}` | Save writes the document's own file in its own format (a document opened from or saved as SVG/PDF saves as that again; the result's `warnings` say what the format loses). With `path` the file is written at once (Save As or a Copy to an SVG path without SVG options first opens SVG Options, below). Without one (never saved, a converted older file, Save As, a Copy, a Template) the app shows a save panel with one file type per save format (`vectorcraft`, `template`, `pdf`, `svg`, `svgz`), then the format's options: SVG opens the `svgOptions` dialog (below; returns `{"pending": "svgOptions", "path"}`), PDF the `savePdf` dialog (its `__save` field names the save command); `ui.dialog.confirm` finishes the save. On the web a `saveOptions` dialog (fields `path`, `format`) first names the file and picks the format. `file.formatOptions {format?}` reads the options a save would use. `file.revert` opens a `confirm` dialog (`{"pending": "confirm"}`); `ui.dialog.confirm` reloads the saved file in the same tab |
+| `file.save` / `file.saveAs` / `file.saveCopy` / `file.saveAsTemplate` (via `engine.execute`) | `{path?, format?, options?, svg?}` | Save writes the document's own file in its own format (a document opened from or saved as SVG/PDF saves as that again; the result's `warnings` say what the format loses). With `path` the file is written at once (Save As or a Copy to an SVG path without SVG options first opens SVG Options, below). Without one (never saved, a converted older file, Save As, a Copy, a Template) the app shows a save panel with one file type per save format (`vectorcraft`, `template`, `pdf`, `svg`, `svgz`), then the format's options: SVG opens the `svgOptions` dialog (below; returns `{"pending": "svgOptions", "path"}`), PDF the `savePdf` dialog (its `__save` field names the save command); `ui.dialog.confirm` finishes the save. A name typed in the panel without the file type's extension gets it; when a file of that name exists, which the panel did not ask about, the save (and every export or other write through a save panel) answers `cancelled` and opens a `replaceFile` dialog (fields `message`, `detail`, `path`): `ui.dialog.confirm` writes that file, `ui.dialog.cancel` writes nothing. On the web a `saveOptions` dialog (fields `path`, `format`) first names the file and picks the format. `file.formatOptions {format?}` reads the options a save would use. `file.revert` opens a `confirm` dialog (`{"pending": "confirm"}`); `ui.dialog.confirm` reloads the saved file in the same tab |
 | SVG Options (`engine.execute` of `file.export.svg`, `file.saveAs`, `file.saveCopy`) | `{}` / `{path?, svg?: {…}}` | `file.export.svg` without params, and Save As or Save a Copy to an `.svg`/`.svgz` path without SVG options, open the `svgOptions` dialog (`ui.dialog.set` its fields: `styling`, `outlineText`, `images`, `objectIds`, `decimals`, `minify`, `responsive`, `fewerTspans`, `metadata`, `preserveEditing`, `useArtboards`, `allArtboards`, `range`, `showCode`, `profile` (`svg11`/`tiny12`), `encoding` (`utf8`/`utf16`/`latin1`), `embedFonts`; `ui.dialog.confirm` exports or saves and remembers the choices). With `svg: {…}` (the `document.formats` SVG options) they run directly. `app.save {path?, svg?}` takes the same options; a document saved as SVG saves as SVG again with the same options |
 | `engine.execute` `file.place` | `{paths?}` / `{path \| name+dataBase64, …file.place params}` | with no file, picks files and opens the `place` dialog; with `paths`, opens it for them (fields `files`, `link`, `template`, `replace`; `__replace` says whether Replace applies, `__info` describes each file). `ui.dialog.confirm` places one file centred in the view (or in place of the selected object) and loads the place cursor with several (`file.place.queue`). With a file, it runs `file.place` centred in the view. Files dropped on the window with no document open open. On the web, files dropped on the canvas are placed at the drop point (linked; Shift embeds) and files dropped off it (the tab bar) open, as in Illustrator; desktop drops carry no pointer position, so documents (native, SVG, PDF, `.ai`, EPS, DXF, EMF/WMF) open as tabs of their own and pictures and text are placed in the middle of the view. Swatch libraries and color books (`.vcswatches`, `.gpl`, `.ase`, `.acb`), graphic style libraries (`.vcstyles`), Libraries panel files (`.vclibrary`), presets (`.vcflattener`, `.vcpdfpresets`, `.vcprintpresets`, `.vcperspective`), plug-ins (`.wasm`) and shortcut sets (`.kys`, in Import Shortcut Set) open wherever they are dropped, as File › Open opens them. With the cursor loaded (`ui.inspect` → `tool: "place"`, `toolOptions: {count, current, name, names}`), `ui.pointer` clicks and drags place files and `ui.key` ←/→/↑/↓ and Escape cycle and discard them |
 | `app.export` raster options | `{path?, format: png \| jpg \| webp, ppi?, background?, antiAlias?, interlaced?, quality?}` | `ppi` sets the pixel size (72 = one pixel per point) and is stored in the file; `background` is `transparent`, `white`, `black` or `"#rrggbb"`; `antiAlias` is `none`, `art` or `type` (text snapped to pixels); `interlaced` writes an Adam7 PNG. The PNG Options dialog (`pngOptions`; `jpgOptions` / `webpOptions` for the other raster formats) has the same fields: fill them with `ui.dialog.set` and press OK with `ui.dialog.confirm` |