refactor(io): set up file association once, not on every launch (#205)

Drop the every-launch (re)registration thread. File association is now set up
once via the first-launch prompt (Yes → register + set default; No → decline,
persisted as file_assoc_enabled) and managed afterwards by the FILEASSOC
command. set_default_app now registers the handler entries (.desktop / mime /
ProgIDs) itself before asking the OS to default to us, since boot no longer
does — so the default never points at a missing handler.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

src/app/mod.rs

@@ -2150,22 +2150,9 @@ impl OpenCADStudio {
     #[cfg(not(target_arch = "wasm32"))]
     fn boot() -> (Self, Task<Message>) {
         use helpers::build_window_icon;
-        // Silently (re)register this binary as a .dwg/.dxf handler so it appears
-        // in the OS "Open with" list. Best-effort and idempotent; covers the
-        // portable .exe / AppImage that no installer has registered. Detached so
-        // it never delays startup.
-        std::thread::spawn(|| {
-            // Honour the FILEASSOC toggle: skip (re)registration when the user
-            // has turned file association off.
-            let enabled = settings::UserSettings::load()
-                .map(|s| s.file_assoc_enabled)
-                .unwrap_or(true);
-            if enabled {
-                if let Err(e) = crate::io::file_association::register_as_handler() {
-                    eprintln!("file association: handler registration failed: {e}");
-                }
-            }
-        });
+        // File association is no longer re-registered on every launch. It is set
+        // up once via the first-launch prompt below (when the user hasn't been
+        // asked yet) and afterwards managed entirely by the FILEASSOC command.
         let state = Self::new();
         let (id, open_task) = window::open(window::Settings {
             maximized: true,

src/app/update/mod.rs

@@ -2590,14 +2590,18 @@ impl OpenCADStudio {
                 Task::none()
             }
             Message::AssocPromptYes => {
+                self.file_assoc_enabled = true;
                 self.mark_assoc_prompted();
                 self.active_modal = None;
+                // set_default_app registers the handler first, then makes us the
+                // default — boot no longer does this automatically.
                 Task::perform(
                     crate::io::file_association::set_default_app(),
                     Message::AssocResult,
                 )
             }
             Message::AssocPromptNo => {
+                self.file_assoc_enabled = false;
                 self.mark_assoc_prompted();
                 self.active_modal = None;
                 Task::none()

src/io/file_association.rs

@@ -96,6 +96,10 @@ pub async fn set_default_app() -> Result<String, String> {
 }
 
 fn set_default_app_blocking() -> Result<String, String> {
+    // Boot no longer auto-registers, so make sure the handler entries (the
+    // .desktop / mime package / ProgIDs) exist before asking the OS to default
+    // to us — otherwise the default would point at nothing.
+    register_as_handler()?;
     #[cfg(target_os = "windows")]
     {
         windows_impl::set_default()