cm: only notify the user once all sessions have closed

remove_connection fired the "session ended" banner for every connection
that closed. With multiple concurrent sessions (a second supporter, or a
file-transfer session running alongside remote control) the user saw one
banner per close even though support was still ongoing.

Track the remaining approved-session count under the same lock and show the
banner only when the last session has ended. Denied/never-approved
connections still produce no banner.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/cm_popup.rs

@@ -140,9 +140,26 @@ impl InvokeUiCM for HeadlessCm {
 
     fn remove_connection(&self, id: i32, _close: bool) {
         trace(&format!("remove_connection: id={id}"));
-        let entry = self.approved.lock().unwrap().remove(&id);
+        // Remove this session and read how many approved sessions remain, while
+        // holding the lock so the check is atomic against concurrent add/remove.
+        let (entry, remaining) = {
+            let mut approved = self.approved.lock().unwrap();
+            let entry = approved.remove(&id);
+            (entry, approved.len())
+        };
         if let Some((peer_id, name)) = entry {
-            std::thread::spawn(move || show_session_ended(&peer_id, &name));
+            // Only notify once EVERY approved session has ended. With multiple
+            // concurrent sessions (a second supporter, or a file-transfer
+            // session running alongside remote control) the user shouldn't get
+            // a "session ended" banner while other sessions are still open —
+            // they'd see one banner per close even though support is ongoing.
+            if remaining == 0 {
+                std::thread::spawn(move || show_session_ended(&peer_id, &name));
+            } else {
+                trace(&format!(
+                    "remove_connection: {remaining} approved session(s) still open; suppressing banner"
+                ));
+            }
         }
     }