app: wire web export, preview, and print flows through the plot UI

- plot dialog: the web build defaults to 'Save to PDF file...' (its only
  output choice); native dropdowns and defaults are untouched.
- on_plot_dlg_commit forces to_file on wasm so a stale page setup can no
  longer route the web build into the (unreachable) printer path; both
  preview branches now go through preview_page_pdf, which is identical to
  the old inline temp-PDF + OS-viewer flow on desktop.
- Print ribbon / PRINTALL on wasm render the PDF and open it in a tab
  instead of erroring; PrintAllPdf picks a virtual path and downloads.
- pdf_plot_options maps the dialog's Quality dropdown into PdfPlotOptions.

(cherry picked from commit 892d693d2d)

src/app/mod.rs

@@ -3712,6 +3712,8 @@ pub enum Message {
     /// Send current layout to the system printer (via lp / lpr).
     PrintToPrinter,
     /// Callback from the async printer job.
+    /// Web never constructs it — printing opens the PDF preview instead.
+    #[cfg_attr(target_arch = "wasm32", allow(dead_code))]
     PrintResult(Result<String, String>),
     /// Open the full Plot / Print dialog (seeds state from the layout).
     PlotDialogOpen,

src/app/update/file.rs

@@ -4160,34 +4160,38 @@ impl OpenCADStudio {
     }
 
     pub(super) fn on_print_all_print(&mut self) -> Task<Message> {
+        let dialog = self.plot_dialog.clone();
+        if self.print_all_settings_override && dialog.style_missing && dialog.apply_plot_styles {
+            self.command_line.push_error(
+                crate::tf!("Plot style table '{}' is not loaded.", dialog.style_name).as_ref(),
+            );
+            return Task::none();
+        }
+        let pages = match self.print_all_pages() {
+            Ok(pages) => pages,
+            Err(error) => {
+                self.command_line.push_error(&error);
+                return Task::none();
+            }
+        };
+        self.save_config();
+        self.close_active_modal();
+        // The web build has no system printers: render every layout into one
+        // PDF and open it in a browser tab for the browser print dialog.
         #[cfg(target_arch = "wasm32")]
         {
-            self.command_line
-                .push_error(crate::t!("Printing is not available in the web version.").as_ref());
-            Task::none()
+            let work = move || {
+                crate::io::print_to_printer::preview_pages_pdf(&pages)
+                    .map(|_| crate::t!("Opened plot preview.").into_owned())
+                    .map_err(|e| crate::tf!("Preview failed: {e}").into_owned())
+            };
+            self.run_print_all_work(true, work)
         }
         #[cfg(not(target_arch = "wasm32"))]
         {
-            let dialog = self.plot_dialog.clone();
-            if self.print_all_settings_override && dialog.style_missing && dialog.apply_plot_styles
-            {
-                self.command_line.push_error(
-                    crate::tf!("Plot style table '{}' is not loaded.", dialog.style_name).as_ref(),
-                );
-                return Task::none();
-            }
-            let pages = match self.print_all_pages() {
-                Ok(pages) => pages,
-                Err(error) => {
-                    self.command_line.push_error(&error);
-                    return Task::none();
-                }
-            };
             let options = self.plot_print_options(&dialog);
             let fallback_style = self.dialog_plot_style(&dialog);
             let temp_path = crate::io::print_to_printer::temp_pdf_path("print_all");
-            self.save_config();
-            self.close_active_modal();
             self.command_line
                 .push_info(crate::t!("Sending selected layouts to the system printer…").as_ref());
             let work = move || {
@@ -4429,18 +4433,35 @@ impl OpenCADStudio {
             );
             return Task::none();
         };
-        let options = self.plot_print_options(&self.plot_dialog);
-        self.command_line
-            .push_info(crate::t!("Sending to system printer…").as_ref());
-        background_task(
-            crate::t!("Print to printer"),
-            move || {
-                iced::futures::executor::block_on(crate::io::print_to_printer::print_wires_with(
-                    page, options,
-                ))
-            },
-            Message::PrintResult,
-        )
+        // The web build has no system printers: PRINT opens the rendered PDF
+        // in a browser tab, where the browser's own print dialog takes over.
+        #[cfg(target_arch = "wasm32")]
+        {
+            background_task(
+                crate::t!("Plot preview"),
+                move || {
+                    crate::io::print_to_printer::preview_page_pdf(&page)
+                        .map(|_| crate::t!("Opened plot preview.").into_owned())
+                        .map_err(|e| crate::tf!("Preview failed: {e}").into_owned())
+                },
+                |result| Message::BackgroundIoFinished(result, false),
+            )
+        }
+        #[cfg(not(target_arch = "wasm32"))]
+        {
+            let options = self.plot_print_options(&self.plot_dialog);
+            self.command_line
+                .push_info(crate::t!("Sending to system printer…").as_ref());
+            background_task(
+                crate::t!("Print to printer"),
+                move || {
+                    iced::futures::executor::block_on(crate::io::print_to_printer::print_wires_with(
+                        page, options,
+                    ))
+                },
+                Message::PrintResult,
+            )
+        }
     }
 
     /// QUICKPRINT / QP — use the current selection's bounding box as the plot
@@ -5743,6 +5764,12 @@ impl OpenCADStudio {
     /// Open a preview PDF, export a PDF, or send the job to the chosen printer.
     fn on_plot_dlg_commit(&mut self, preview: bool) -> Task<Message> {
         let d = self.plot_dialog.clone();
+        // The web dialog only offers PDF output, but a page setup loaded from
+        // the drawing can still seed `to_file = false` — always export there.
+        #[cfg(target_arch = "wasm32")]
+        let to_file = true;
+        #[cfg(not(target_arch = "wasm32"))]
+        let to_file = d.to_file;
         if d.style_missing && d.apply_plot_styles {
             self.command_line.push_error(
                 crate::tf!("Plot style table '{}' is not loaded.", d.style_name).as_ref(),
@@ -5788,16 +5815,14 @@ impl OpenCADStudio {
             // Preview renders to a temp PDF and opens it — never a save dialog,
             // whatever the output target is.
             if preview {
-                let tmp = crate::io::print_to_printer::temp_pdf_path("preview");
                 let work = move || {
-                    crate::io::pdf_export::export_pdf(&page, &tmp)
-                        .and_then(|_| crate::io::print_to_printer::open_in_viewer(&tmp))
+                    crate::io::print_to_printer::preview_page_pdf(&page)
                         .map(|_| crate::t!("Opened plot preview.").into_owned())
                         .map_err(|e| crate::tf!("Preview failed: {e}").into_owned())
                 };
                 return self.run_plot_work(d.background, true, work);
             }
-            if d.to_file {
+            if to_file {
                 // Tested clipped export (opens a save dialog).
                 return Task::done(Message::PlotWindowExport);
             }
@@ -5815,17 +5840,15 @@ impl OpenCADStudio {
         let page = self.layout_plot_page();
 
         if preview {
-            let tmp = crate::io::print_to_printer::temp_pdf_path("preview");
             let work = move || {
-                crate::io::pdf_export::export_pdf(&page, &tmp)
-                    .and_then(|_| crate::io::print_to_printer::open_in_viewer(&tmp))
+                crate::io::print_to_printer::preview_page_pdf(&page)
                     .map(|_| crate::t!("Opened plot preview.").into_owned())
                     .map_err(|e| crate::tf!("Preview failed: {e}").into_owned())
             };
             return self.run_plot_work(d.background, true, work);
         }
 
-        if d.to_file {
+        if to_file {
             // Reuse the tested PDF export flow (it opens a save dialog).
             return Task::done(Message::PlotExport);
         }

src/app/update/mod.rs

@@ -9936,11 +9936,10 @@ impl OpenCADStudio {
                 }
                 #[cfg(target_arch = "wasm32")]
                 {
-                    let _ = stem;
-                    self.command_line.push_error(
-                        crate::t!("PDF export is not available in the web version.").as_ref(),
-                    );
-                    Task::none()
+                    Task::perform(
+                        crate::io::pdf_export::pick_pdf_path_owned(stem),
+                        Message::PrintAllPdfPath,
+                    )
                 }
             }
             Message::PrintAllPdfPath(None) => Task::none(),

src/ui/window/plot.rs

@@ -3,6 +3,8 @@
 //! quality and output options into one dialog; on commit it either sends the
 //! current layout to a system printer (with the chosen options) or writes a
 //! PDF. Styled to match the other OCS dialogs (dark pills + fields).
+//! The web build has no system printers, so PDF is the only output it
+//! offers — and its default.
 
 use crate::app::Message;
 use crate::io::paper_catalog::{self, CustomPaper, Margins, PaperSize, PaperUnits};
@@ -599,7 +601,8 @@ impl Default for PlotDialogState {
             import_draft: None,
             page_setup_on_new_layout: false,
             printer: None,
-            to_file: false,
+            // Web defaults to PDF output: it has no system printers.
+            to_file: cfg!(target_arch = "wasm32"),
             file_svg: false,
             paper: paper_catalog::default_paper().canonical.to_string(),
             paper_width_mm: 297.0,
@@ -1144,6 +1147,25 @@ fn custom_paper_editor<'a>(draft: &'a CustomPaperDraft, width: Length) -> Elemen
     .into()
 }
 
+/// Entries for the output dropdown. The web build has no system printers, so
+/// PDF is the only output it offers; native lists the system default, every
+/// discovered printer, then PDF.
+fn output_choices(printers: &[String]) -> Vec<PlotChoice> {
+    #[cfg(target_arch = "wasm32")]
+    {
+        let _ = printers;
+        vec![PlotChoice::localized(OUT_PDF)]
+    }
+    #[cfg(not(target_arch = "wasm32"))]
+    {
+        let mut out = vec![PlotChoice::localized(OUT_DEFAULT)];
+        out.extend(printers.iter().cloned().map(PlotChoice::raw));
+        out.push(PlotChoice::localized(OUT_PDF));
+        out.push(PlotChoice::localized(OUT_SVG));
+        out
+    }
+}
+
 pub fn view_window(
     s: &PlotDialogState,
     print_all_options: bool,
@@ -1151,10 +1173,17 @@ pub fn view_window(
 ) -> Element<'_, Message> {
     let width = sizing.width;
     let height = sizing.height;
+    // The web build always outputs PDF, whatever a stored dialog state says;
+    // native follows the stored choice.
+    #[cfg(target_arch = "wasm32")]
+    let to_file = true;
+    #[cfg(not(target_arch = "wasm32"))]
+    let to_file = s.to_file;
     let action = if print_all_options {
         t!("Apply")
-    } else if s.to_file {
-        if s.file_svg {
+    } else if to_file {
+        // The web build writes PDF whatever a stored dialog state says.
+        if s.file_svg && cfg!(not(target_arch = "wasm32")) {
             t!("Export SVG")
         } else {
             t!("Export PDF")
@@ -1289,12 +1318,21 @@ pub fn view_window(
         },
         None => PlotChoice::localized(OUT_DEFAULT),
     };
-    let mut printer_opts = vec![default_entry.clone()];
-    printer_opts.extend(s.printers.iter().cloned().map(PlotChoice::raw));
-    printer_opts.push(PlotChoice::localized(OUT_PDF));
-    printer_opts.push(PlotChoice::localized(OUT_SVG));
-    let printer_sel = if s.to_file {
-        Some(PlotChoice::localized(if s.file_svg { OUT_SVG } else { OUT_PDF }))
+    let mut printer_opts = output_choices(&s.printers);
+    if let Some(first) = printer_opts
+        .first_mut()
+        .filter(|first| first.raw == OUT_DEFAULT)
+    {
+        *first = default_entry.clone();
+    }
+    let printer_sel = if to_file {
+        Some(PlotChoice::localized(
+            if s.file_svg && cfg!(not(target_arch = "wasm32")) {
+                OUT_SVG
+            } else {
+                OUT_PDF
+            },
+        ))
     } else {
         Some(match &s.printer {
             Some(printer) => PlotChoice::raw(printer.clone()),
@@ -1373,7 +1411,7 @@ pub fn view_window(
     .spacing(8)
     .align_y(iced::Center)
     .width(Length::Fill);
-    let printer_controls: Element<'_, Message> = if s.to_file {
+    let printer_controls: Element<'_, Message> = if to_file {
         Space::new().height(0).into()
     } else {
         row![