goblin: return to the calling app after a successful sign-in or authorize (Build 151)

android/app/src/main/java/mw/gri/android/MainActivity.java

@@ -402,6 +402,15 @@ public class MainActivity extends GameActivity {
         finishAndRemoveTask();
     }
 
+    // Called from native code after a successful same-device sign-in/authorize
+    // to hand focus back to the app that deep-linked into us (the browser tab
+    // that is polling the callback). Backgrounds our task so the OS surfaces the
+    // previous app; keeps the process alive (unlike exit()) so the callback POST
+    // finishes and the success toast shows on next foreground.
+    public void returnToCaller() {
+        moveTaskToBack(true);
+    }
+
     @Override
     protected void onDestroy() {
         unregisterReceiver(mBroadcastReceiver);

src/gui/platform/android/mod.rs

@@ -286,6 +286,12 @@ impl PlatformCallbacks for Android {
 	fn vibrate_copy(&self) {
 		let _ = self.call_java_method("vibrateCopy", "()V", &[]);
 	}
+
+	fn return_to_caller(&self) {
+		// Background our task (Activity.moveTaskToBack(true), wrapped Java-side)
+		// so the OS brings the app that deep-linked into us back to the front.
+		let _ = self.call_java_method("returnToCaller", "()V", &[]);
+	}
 }
 
 lazy_static! {

src/gui/platform/mod.rs

@@ -76,4 +76,12 @@ pub trait PlatformCallbacks {
 
 	/// Play a tiny "tick" haptic confirming a successful copy. No-op off Android.
 	fn vibrate_copy(&self) {}
+
+	/// Return the user to the app that deep-linked into Goblin (the same-device
+	/// app-switch flow: a browser hands off a `goblin:login`/`goblin:authorize`
+	/// URI, we sign, then hand focus back). On Android this backgrounds our task
+	/// so the OS surfaces the previous app (the polling browser tab). Best-effort
+	/// and a no-op off Android, where there is no clean "return focus" primitive
+	/// (egui/winit); desktop leaves the window where it is.
+	fn return_to_caller(&self) {}
 }