feat(plugin): uninstall + clean upgrade/reinstall of external plugins

Add an Uninstall button on installed external plugin cards that deletes
the package folder (effective next restart — the library stays resident
for the session). Reinstalling or upgrading via the marketplace now
clears any stale native library with a different name before writing the
new one, so the loader always picks the freshly installed binary.

Part of the #100 extensibility epic (phase 2).

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

src/app/mod.rs

@@ -1073,6 +1073,8 @@ pub enum Message {
     PluginInstall(String),
     /// Result of an install: the plugin id, or an error message.
     PluginInstalled(Result<String, String>),
+    /// Delete an installed plugin's folder (effective next restart).
+    PluginUninstall(String),
     // ── Point Style (DDPTYPE) dialog ──────────────────────────────────────
     /// Set the full PDMODE value from a glyph-grid cell.
     PointStyleSetMode(i16),

src/app/update.rs

@@ -5699,6 +5699,24 @@ impl OpenCADStudio {
                 self.marketplace_status = format!("Install failed: {e}");
                 Task::none()
             }
+            Message::PluginUninstall(id) => {
+                #[cfg(not(target_arch = "wasm32"))]
+                {
+                    match crate::plugin::external::uninstall(&id) {
+                        Ok(()) => {
+                            self.marketplace_status =
+                                format!("Uninstalled '{id}'. Restart to unload it.");
+                            self.external_plugins = crate::plugin::external::discover();
+                        }
+                        Err(e) => {
+                            self.marketplace_status = format!("Uninstall failed: {e}");
+                        }
+                    }
+                }
+                #[cfg(target_arch = "wasm32")]
+                let _ = id;
+                Task::none()
+            }
             Message::PointStyleSetMode(mode) => {
                 self.set_point_mode_bits(!0, mode);
                 Task::none()

src/plugin/external.rs

@@ -76,6 +76,16 @@ pub fn plugins_dir() -> Option<PathBuf> {
     Some(p)
 }
 
+/// Delete an installed package's folder. It stays loaded for the current
+/// session (the library is resident); the removal takes effect on next start.
+pub fn uninstall(id: &str) -> Result<(), String> {
+    let dir = plugins_dir().ok_or("cannot locate the plugins folder")?.join(id);
+    if dir.is_dir() {
+        std::fs::remove_dir_all(&dir).map_err(|e| e.to_string())?;
+    }
+    Ok(())
+}
+
 /// Native dynamic-library extension for the current platform (no dot).
 fn lib_extension() -> &'static str {
     if cfg!(target_os = "windows") {

src/plugin/marketplace.rs

@@ -192,6 +192,19 @@ pub fn install(release: &Release) -> Result<String, String> {
     std::fs::create_dir_all(&dir).map_err(|e| e.to_string())?;
 
     let bytes = download_bytes(&lib.url)?;
+    // Clean upgrade / reinstall: drop any previously-installed native library
+    // with a different name so the loader doesn't pick a stale one. The
+    // currently-resident library (if loaded) keeps running until restart.
+    let ext = external_lib_ext();
+    if let Ok(rd) = std::fs::read_dir(&dir) {
+        for old in rd.flatten() {
+            let p = old.path();
+            let is_lib = p.extension().and_then(|s| s.to_str()) == Some(ext);
+            if is_lib && p.file_name().and_then(|s| s.to_str()) != Some(lib.name.as_str()) {
+                let _ = std::fs::remove_file(&p);
+            }
+        }
+    }
     std::fs::write(dir.join(&lib.name), bytes).map_err(|e| e.to_string())?;
     std::fs::write(dir.join("plugin.toml"), toml_text).map_err(|e| e.to_string())?;
     Ok(manifest.id)

src/ui/plugin_manager.rs

@@ -150,6 +150,12 @@ fn external_card<'a>(p: &ExternalPlugin, loaded: bool, disabled: bool) -> Elemen
         header = header.push(Space::new().width(10));
         header = header.push(toggle_button(&p.id, disabled));
     }
+    header = header.push(Space::new().width(6));
+    header = header.push(pill_button(
+        "Uninstall",
+        Message::PluginUninstall(p.id.clone()),
+        Color { r: 0.4, g: 0.25, b: 0.25, a: 1.0 },
+    ));
 
     let id_line = text(p.id.clone()).size(11).color(ACCENT);
     let mut body = column![header, id_line].spacing(5);