macOS launcher: re-assert Accessory policy after handling an event

Handling a document-open Apple Event (a warm "Open With" while the app
is already running) silently promotes this process from
NSApplicationActivationPolicyAccessory to a normal foreground app —
confirmed with lsappinfo, not assumed: its own entry flips from
type="UIElement" to type="Foreground" the instant it handles a second
Apple Event (a cold launch's own first event doesn't trigger this).
That gave the launcher its own, contentless Dock icon sitting next to
the real editor's, both apparently "the same app" to the user but
actually two separate Dock entries.

Re-set Accessory explicitly right after relaying, in the one place
every open (cold fallback, document open, and reopen-while-running)
already funnels through.

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

src/bin/ocs_launcher.rs

@@ -103,13 +103,32 @@ fn real_binary_path() -> PathBuf {
 /// running or about to claim it on its own.
 fn deliver_or_launch(files: &[String]) {
     let paths: Vec<PathBuf> = files.iter().map(PathBuf::from).collect();
-    if let Some(stream) = single_instance::try_connect_existing() {
-        if single_instance::handoff(stream, &paths) {
-            return;
+    let delivered = single_instance::try_connect_existing()
+        .map(|stream| single_instance::handoff(stream, &paths))
+        .unwrap_or(false);
+    if !delivered {
+        if let Err(err) = std::process::Command::new(real_binary_path()).args(files).spawn() {
+            eprintln!("OpenCADStudio launcher: failed to launch the real binary: {err}");
         }
     }
-    if let Err(err) = std::process::Command::new(real_binary_path()).args(files).spawn() {
-        eprintln!("OpenCADStudio launcher: failed to launch the real binary: {err}");
+    reassert_accessory_policy();
+}
+
+/// AppKit activates this process — promoting it from
+/// NSApplicationActivationPolicyAccessory (no Dock icon, set at startup) to
+/// a normal foreground app with its own Dock icon — as a side effect of
+/// handling an open-document Apple Event, even though nothing here ever
+/// shows a window. Measured via `lsappinfo`, not assumed: the launcher's own
+/// entry flips from type="UIElement" to type="Foreground" the moment it
+/// handles a *second* Apple Event (a fresh cold launch's own first event
+/// doesn't trigger this — the policy is presumably still settling at that
+/// point). Set it back immediately after relaying, so a warm "Open With"
+/// doesn't leave a second, contentless Dock icon sitting next to the real
+/// editor's.
+fn reassert_accessory_policy() {
+    if let Some(mtm) = MainThreadMarker::new() {
+        NSApplication::sharedApplication(mtm)
+            .setActivationPolicy(NSApplicationActivationPolicy::Accessory);
     }
 }