feat(plugin): ModuleEvent::PluginFileDialog for native file import

Add-ons had no way to request a file picker — only the host's own Open
dialog. PluginFileDialog lets a plugin tool ask the host to open a native
picker; on selection the host dispatches "<command> <path>" back to the
plugin with original case preserved (bypassing the command-line
upper-casing that mangles case-sensitive paths on Linux/macOS). The demo
plugin gains an Import tool exercising it.

Part of the #100 extensibility epic (surfaced in #106).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

crates/ocs_plugin_api/src/ribbon.rs

@@ -17,6 +17,21 @@ pub enum ModuleEvent {
     SetWireframe(bool),
     /// Toggle the layer manager panel.
     ToggleLayers,
+    /// Ask the host to open a native file picker. On selection the host
+    /// dispatches `"<command> <path>"` back to the plugin (full original case,
+    /// bypassing the command line so case-sensitive paths/args survive); on
+    /// cancel nothing happens. Lets an add-on import files without owning any
+    /// dialog UI.
+    PluginFileDialog {
+        /// Plugin command to dispatch with the chosen path appended.
+        command: String,
+        /// Dialog window title.
+        title: String,
+        /// Human label for the file-type filter (e.g. "PNEZD Points").
+        filter_name: String,
+        /// Accepted extensions, without the dot (e.g. `["csv", "txt"]`).
+        extensions: Vec<String>,
+    },
 }
 
 // ── Data types ────────────────────────────────────────────────────────────

docs/plugin-architecture.md

@@ -257,6 +257,7 @@ This mirrors QGIS: the application ships core menus; plugins add tabs/tools with
 - [~] Extract `ocs_plugin_api` crate — manifest + ribbon/`CadModule` done; `acadrust`-typed host surface pending
 - [x] Plugin manager UI (list installed, versions) — `PLUGINS` / `PLUGINMANAGER` command, or the Start-page "Plugins" button
 - [x] Enable/disable plugins from the manager — a disabled plugin drops its ribbon tab and command dispatch; persisted in `settings.txt` (`disabled_plugins=`)
+- [x] `ModuleEvent::PluginFileDialog` — a plugin tool requests a native file picker; the host opens it and dispatches `"<command> <path>"` back to the plugin with original case preserved (bypasses the command-line upper-casing)
 
 ### Phase 2 — Dynamic loading (desktop)
 

src/app/mod.rs

@@ -722,6 +722,13 @@ pub enum Message {
         tool_id: String,
         event: ModuleEvent,
     },
+    /// Result of a plugin-requested file picker (`ModuleEvent::PluginFileDialog`).
+    /// `path` is `None` when the user cancels. On `Some`, the host dispatches
+    /// `"<command> <path>"` to the plugins with original case preserved.
+    PluginFileDialogResult {
+        command: String,
+        path: Option<std::path::PathBuf>,
+    },
     // ── Application menu ──────────────────────────────────────────────────
     ToggleAppMenu,
     CloseAppMenu,

src/app/update.rs

@@ -1027,6 +1027,42 @@ impl OpenCADStudio {
                     ModuleEvent::ToggleLayers => {
                         return Task::done(Message::ToggleLayers);
                     }
+                    ModuleEvent::PluginFileDialog {
+                        command,
+                        title,
+                        filter_name,
+                        extensions,
+                    } => {
+                        return Task::perform(
+                            async move {
+                                let exts: Vec<&str> =
+                                    extensions.iter().map(|s| s.as_str()).collect();
+                                let path = rfd::AsyncFileDialog::new()
+                                    .set_title(title)
+                                    .add_filter(filter_name, &exts)
+                                    .add_filter("All Files", &["*"])
+                                    .pick_file()
+                                    .await
+                                    .map(|h| crate::sys::handle_path(&h));
+                                (command, path)
+                            },
+                            |(command, path)| Message::PluginFileDialogResult { command, path },
+                        );
+                    }
+                }
+                Task::none()
+            }
+            Message::PluginFileDialogResult { command, path } => {
+                if let Some(path) = path {
+                    // Dispatch "<command> <path>" with original case intact —
+                    // the command line would upper-case the whole string and
+                    // mangle case-sensitive paths on Linux/macOS.
+                    let line = format!("{} {}", command, path.to_string_lossy());
+                    let i = self.active_tab;
+                    if !crate::plugin::try_dispatch(self, i, &line) {
+                        self.command_line
+                            .push_error(&format!("No plugin handled: {command}"));
+                    }
                 }
                 Task::none()
             }

src/modules/demo_plugin/dispatch.rs

@@ -1,6 +1,12 @@
 use crate::plugin::host::HostSession;
 
 pub fn handle(host: &mut HostSession<'_>, cmd: &str) -> bool {
+    // "DP_IMPORT <path>" arrives from ModuleEvent::PluginFileDialog with the
+    // path in its original case (the command line is bypassed).
+    if let Some(path) = cmd.strip_prefix("DP_IMPORT ") {
+        host.push_info(&format!("demo_plugin imported: {path}"));
+        return true;
+    }
     match cmd {
         "DP_HELLO" => {
             host.push_info("Hello from demo_plugin (plugin host OK).");

src/modules/demo_plugin/mod.rs

@@ -8,7 +8,7 @@ pub mod register;
 use crate::modules::{CadModule, IconKind, ModuleEvent, RibbonGroup, RibbonItem, ToolDef};
 
 inventory::submit!(crate::command::CommandRegistration {
-    names: &["DP_HELLO"]
+    names: &["DP_HELLO", "DP_IMPORT"]
 });
 
 pub struct DemoPluginModule;
@@ -25,12 +25,27 @@ impl CadModule for DemoPluginModule {
     fn ribbon_groups(&self) -> Vec<RibbonGroup> {
         vec![RibbonGroup {
             title: "Smoke",
-            tools: vec![RibbonItem::LargeTool(ToolDef {
+            tools: vec![
+                RibbonItem::LargeTool(ToolDef {
                     id: "DP_HELLO",
                     label: "Hello",
                     icon: IconKind::Glyph("★"),
                     event: ModuleEvent::Command("DP_HELLO".to_string()),
-            })],
+                }),
+                // Exercises ModuleEvent::PluginFileDialog: the host opens a
+                // native picker and dispatches "DP_IMPORT <path>" back here.
+                RibbonItem::LargeTool(ToolDef {
+                    id: "DP_IMPORT",
+                    label: "Import",
+                    icon: IconKind::Glyph("📂"),
+                    event: ModuleEvent::PluginFileDialog {
+                        command: "DP_IMPORT".to_string(),
+                        title: "Import Demo File".to_string(),
+                        filter_name: "Text".to_string(),
+                        extensions: vec!["txt".to_string(), "csv".to_string()],
+                    },
+                }),
+            ],
         }]
     }
 }

src/plugin/registry.rs

@@ -139,6 +139,20 @@ mod tests {
         );
     }
 
+    #[test]
+    fn plugin_file_dialog_dispatch_preserves_case() {
+        // ModuleEvent::PluginFileDialog dispatches "<command> <path>" verbatim;
+        // the mixed-case path must reach the plugin unaltered.
+        let mut app = OpenCADStudio::new_for_test();
+        let line = "DP_IMPORT /home/User/My Points.CSV";
+        assert!(try_dispatch(&mut app, 0, line));
+        let info = app.command_history_info();
+        assert!(
+            info.iter().any(|t| t.contains("/home/User/My Points.CSV")),
+            "path case not preserved; info: {info:?}"
+        );
+    }
+
     #[test]
     fn unknown_plugin_command_falls_through() {
         let mut app = OpenCADStudio::new_for_test();

src/ui/ribbon/widgets.rs

@@ -1269,6 +1269,12 @@ pub fn module_event_to_message(event: ModuleEvent) -> Message {
         ModuleEvent::ClearModels => Message::ClearScene,
         ModuleEvent::SetWireframe(w) => Message::SetWireframe(w),
         ModuleEvent::ToggleLayers => Message::ToggleLayers,
+        // Needs the tool context + async picker — route through the normal
+        // ribbon-click handler rather than a direct 1:1 message.
+        e @ ModuleEvent::PluginFileDialog { .. } => Message::RibbonToolClick {
+            tool_id: String::new(),
+            event: e,
+        },
     }
 }