feat(dialogs): reopen file pickers in the last-used directory

Every rfd dialog result funnels through sys::handle_path, which now
records the picked file's folder (persisted to the config dir), and all
pickers are built via sys::file_dialog(), seeded with that folder.
Save-As keeps the current tab's own directory as the first choice and
falls back to the remembered one.

Co-Authored-By: Claude Fable 5 <[email protected]>

src/app/update/dialog.rs

@@ -153,7 +153,7 @@ pub(super) fn on_ribbon_tool_click(&mut self, tool_id: String, event: ModuleEven
                             async move {
                                 let exts: Vec<&str> =
                                     extensions.iter().map(|s| s.as_str()).collect();
-                                let path = rfd::AsyncFileDialog::new()
+                                let path = crate::sys::file_dialog()
                                     .set_title(title)
                                     .add_filter(filter_name, &exts)
                                     .add_filter("All Files", &["*"])

src/app/update/file.rs

@@ -845,7 +845,7 @@ pub(super) fn on_open_file(&mut self) -> Task<Message> {
                     let close = self.close_save_dialog_window();
                     let pick = Task::perform(
                         async move {
-                            let mut dlg = rfd::AsyncFileDialog::new()
+                            let mut dlg = crate::sys::file_dialog()
                                 .set_title("Save Drawing As")
                                 .set_file_name(default_name)
                                 .add_filter(filter_label, &[filter_ext]);
@@ -2204,7 +2204,7 @@ pub(super) fn on_open_file(&mut self) -> Task<Message> {
                     .unwrap_or("export.ctb".into());
                 Task::perform(
                     async move {
-                        rfd::AsyncFileDialog::new()
+                        crate::sys::file_dialog()
                             .set_title("Save Plot Style Table")
                             .set_file_name(&default_name)
                             .add_filter("Plot Style Files", &["ctb", "stb", "CTB", "STB"])

src/app/update/mod.rs

@@ -408,7 +408,7 @@ impl OpenCADStudio {
 
             Message::XAttachPick => Task::perform(
                 async {
-                    let handle = rfd::AsyncFileDialog::new()
+                    let handle = crate::sys::file_dialog()
                         .set_title("Select External Reference File")
                         .add_filter("CAD Files", &["dwg", "dxf", "bak", "DWG", "DXF", "BAK"])
                         .add_filter("DWG Files", &["dwg", "DWG"])
@@ -446,7 +446,7 @@ impl OpenCADStudio {
                 let name = block_name.clone();
                 Task::perform(
                     async move {
-                        let path = rfd::AsyncFileDialog::new()
+                        let path = crate::sys::file_dialog()
                             .set_title("Save Block As")
                             .set_file_name("block.dwg")
                             .add_filter("DWG Files", &["dwg"])
@@ -469,7 +469,7 @@ impl OpenCADStudio {
                 let csv_clone = csv.clone();
                 Task::perform(
                     async move {
-                        let path = rfd::AsyncFileDialog::new()
+                        let path = crate::sys::file_dialog()
                             .set_title("Save Data Extraction")
                             .set_file_name("extraction.csv")
                             .add_filter("CSV", &["csv"])
@@ -512,7 +512,7 @@ impl OpenCADStudio {
                 }
                 Task::perform(
                     async {
-                        rfd::AsyncFileDialog::new()
+                        crate::sys::file_dialog()
                             .set_title("Export STL")
                             .set_file_name("export.stl")
                             .add_filter("STL Files", &["stl"])
@@ -539,7 +539,7 @@ impl OpenCADStudio {
                 }
                 Task::perform(
                     async {
-                        rfd::AsyncFileDialog::new()
+                        crate::sys::file_dialog()
                             .set_title("Export STEP AP203")
                             .set_file_name("export.step")
                             .add_filter("STEP Files", &["step", "stp"])
@@ -559,7 +559,7 @@ impl OpenCADStudio {
             // ── OBJ import ────────────────────────────────────────────────
             Message::ObjImport => Task::perform(
                 async {
-                    rfd::AsyncFileDialog::new()
+                    crate::sys::file_dialog()
                         .set_title("Import OBJ Mesh")
                         .add_filter("Wavefront OBJ", &["obj", "OBJ"])
                         .add_filter("All Files", &["*"])

src/config.rs

@@ -28,3 +28,45 @@ pub fn config_dir() -> Option<PathBuf> {
     p.push("OpenCADStudio");
     Some(p)
 }
+
+// ── Last file-dialog directory ───────────────────────────────────────────────
+
+use std::path::Path;
+use std::sync::{Mutex, OnceLock};
+
+fn last_dir_store() -> &'static Mutex<Option<PathBuf>> {
+    static STORE: OnceLock<Mutex<Option<PathBuf>>> = OnceLock::new();
+    STORE.get_or_init(|| {
+        // Seed from the persisted value; discard it if the folder is gone.
+        let loaded = config_dir()
+            .map(|d| d.join("last_dir.txt"))
+            .and_then(|f| std::fs::read_to_string(f).ok())
+            .map(|s| PathBuf::from(s.trim()))
+            .filter(|p| p.is_dir());
+        Mutex::new(loaded)
+    })
+}
+
+/// The directory the last file dialog picked or saved into, if it still
+/// exists — used to seed the next dialog so pickers reopen where the user
+/// left off. Persisted across runs.
+pub fn last_dialog_dir() -> Option<PathBuf> {
+    last_dir_store().lock().ok()?.clone().filter(|p| p.is_dir())
+}
+
+/// Record the directory of a path a file dialog just returned.
+pub fn remember_dialog_dir(file_path: &Path) {
+    let Some(dir) = file_path.parent().filter(|d| d.is_dir()) else {
+        return;
+    };
+    if let Ok(mut store) = last_dir_store().lock() {
+        if store.as_deref() == Some(dir) {
+            return; // unchanged — skip the disk write
+        }
+        *store = Some(dir.to_path_buf());
+    }
+    if let Some(cfg) = config_dir() {
+        let _ = std::fs::create_dir_all(&cfg);
+        let _ = std::fs::write(cfg.join("last_dir.txt"), dir.display().to_string());
+    }
+}

src/io/mod.rs

@@ -40,7 +40,7 @@ const PHASE_FINALIZING: u8 = 3;
 /// the parser thread starts.
 #[cfg(not(target_arch = "wasm32"))]
 pub async fn pick_open_path() -> Option<(PathBuf, u64)> {
-    let handle = rfd::AsyncFileDialog::new()
+    let handle = crate::sys::file_dialog()
         .set_title("Open CAD file")
         .add_filter("CAD Files", &["dwg", "dxf", "bak", "sv$", "DWG", "DXF", "BAK"])
         .add_filter("DWG Files", &["dwg", "DWG"])
@@ -103,7 +103,7 @@ pub async fn open_path_with_phase(
 #[cfg(target_arch = "wasm32")]
 pub async fn pick_and_load_web(
 ) -> Result<(String, PathBuf, CadDocument, DerivedCaches), String> {
-    let handle = rfd::AsyncFileDialog::new()
+    let handle = crate::sys::file_dialog()
         .set_title("Open CAD file")
         .add_filter("CAD Files", &["dwg", "dxf", "DWG", "DXF"])
         .add_filter("All Files", &["*"])
@@ -364,7 +364,7 @@ pub fn write_backup(path: &std::path::Path) {
 
 /// Show a file-open dialog and load the selected CTB or STB file.
 pub async fn pick_plot_style() -> Option<plot_style::PlotStyleTable> {
-    let handle = rfd::AsyncFileDialog::new()
+    let handle = crate::sys::file_dialog()
         .set_title("Load Plot Style Table")
         .add_filter("Plot Style Tables", &["ctb", "stb", "CTB", "STB"])
         .add_filter("CTB Files", &["ctb", "CTB"])
@@ -380,7 +380,7 @@ pub async fn pick_plot_style() -> Option<plot_style::PlotStyleTable> {
 /// Show a file-open dialog for raster images and decode the selected file.
 /// Returns `(path, pixel_width, pixel_height)` or an error string.
 pub async fn pick_image_file() -> Result<(PathBuf, u32, u32), String> {
-    let handle = rfd::AsyncFileDialog::new()
+    let handle = crate::sys::file_dialog()
         .set_title("Select Image File")
         .add_filter("Images", &["png", "jpg", "jpeg", "bmp", "tiff", "tif"])
         .add_filter("PNG", &["png"])

src/io/pdf_export.rs

@@ -100,7 +100,7 @@ pub fn export_pdf(
 /// Show a PDF save-file dialog and return the chosen path (or None if cancelled).
 #[cfg(not(target_arch = "wasm32"))]
 pub async fn pick_pdf_path_owned(stem: String) -> Option<std::path::PathBuf> {
-    rfd::AsyncFileDialog::new()
+    crate::sys::file_dialog()
         .set_title("Export as PDF")
         .set_file_name(&format!("{stem}.pdf"))
         .add_filter("PDF Files", &["pdf"])

src/sys.rs

@@ -39,7 +39,11 @@ pub async fn read_clipboard_text() -> Option<String> {
 /// (a follow-up).
 #[cfg(not(target_arch = "wasm32"))]
 pub fn handle_path(h: &rfd::FileHandle) -> std::path::PathBuf {
-    h.path().to_path_buf()
+    let p = h.path().to_path_buf();
+    // Every dialog result funnels through here — remember its folder so the
+    // next dialog opens where the user left off.
+    crate::config::remember_dialog_dir(&p);
+    p
 }
 
 #[cfg(target_arch = "wasm32")]
@@ -47,6 +51,23 @@ pub fn handle_path(h: &rfd::FileHandle) -> std::path::PathBuf {
     std::path::PathBuf::from(h.file_name())
 }
 
+/// New async file dialog seeded with the last directory a dialog was used in.
+/// All pickers should start from this instead of `rfd::AsyncFileDialog::new()`.
+#[cfg(not(target_arch = "wasm32"))]
+pub fn file_dialog() -> rfd::AsyncFileDialog {
+    let dlg = rfd::AsyncFileDialog::new();
+    match crate::config::last_dialog_dir() {
+        Some(dir) => dlg.set_directory(dir),
+        None => dlg,
+    }
+}
+
+/// Web: no filesystem paths, nothing to remember.
+#[cfg(target_arch = "wasm32")]
+pub fn file_dialog() -> rfd::AsyncFileDialog {
+    rfd::AsyncFileDialog::new()
+}
+
 /// Trigger a browser download of `bytes` as `name`. Builds a Blob, points a
 /// hidden `<a download>` at it and clicks it programmatically — because this
 /// runs inside the Save button's click (a user gesture), the file downloads