fix: use single-intent shortcut so FLAG_ACTIVITY_NEW_DOCUMENT task matching works

FLAG_ACTIVITY_NEW_DOCUMENT document-task matching (same URI → reuse
existing task) only works with single-intent startActivity(). When
ShortcutInfoCompat.setIntents() passes a multi-intent array, Android
internally calls startActivities(), which does not honour the document-
task model: different shortcuts end up sharing a task, and opening the
same app from chat and from a shortcut creates duplicate tasks.

Fix: replace setIntents(getWebxdcIntentWithParentStack()) with
setIntent(getWebxdcIntent()) so the shortcut fires the exact same
single intent as a direct open. The now-unused
getWebxdcIntentWithParentStack helper and TaskStackBuilder import
are removed.

src/main/java/org/thoughtcrime/securesms/WebxdcActivity.java

@@ -28,7 +28,6 @@ import android.widget.Toast;
 import androidx.annotation.NonNull;
 import androidx.annotation.RequiresApi;
 import androidx.appcompat.app.ActionBar;
-import androidx.core.app.TaskStackBuilder;
 import androidx.core.content.pm.ShortcutInfoCompat;
 import androidx.core.content.pm.ShortcutManagerCompat;
 import androidx.core.graphics.drawable.IconCompat;
@@ -133,30 +132,20 @@ public class WebxdcActivity extends WebViewActivity implements DcEventCenter.DcE
   private static Intent getWebxdcIntent(
       Context context, int msgId, boolean hideActionBar, String href) {
     DcContext dcContext = DcHelper.getContext(context);
+    int accountId = dcContext.getAccountId();
     Intent intent = new Intent(context, WebxdcActivity.class);
     intent.setAction(Intent.ACTION_VIEW);
-    intent.putExtra(EXTRA_ACCOUNT_ID, dcContext.getAccountId());
+    // Unique URI per webxdc instance so FLAG_ACTIVITY_NEW_DOCUMENT can identify the document:
+    // same app → same URI → existing task reused; different apps → different URIs → separate tasks.
+    intent.setData(Uri.parse("webxdc://" + accountId + "/" + msgId));
+    intent.putExtra(EXTRA_ACCOUNT_ID, accountId);
     intent.putExtra(EXTRA_APP_MSG_ID, msgId);
     intent.putExtra(EXTRA_HIDE_ACTION_BAR, hideActionBar);
     intent.putExtra(EXTRA_HREF, href);
+    intent.addFlags(Intent.FLAG_ACTIVITY_NEW_DOCUMENT);
     return intent;
   }
 
-  private static Intent[] getWebxdcIntentWithParentStack(Context context, int msgId) {
-    DcContext dcContext = DcHelper.getContext(context);
-
-    final Intent chatIntent =
-        new Intent(context, ConversationActivity.class)
-            .putExtra(ConversationActivity.CHAT_ID_EXTRA, dcContext.getMsg(msgId).getChatId())
-            .setAction(Intent.ACTION_VIEW);
-
-    final Intent webxdcIntent = getWebxdcIntent(context, msgId, false, "");
-
-    return TaskStackBuilder.create(context)
-        .addNextIntentWithParentStack(chatIntent)
-        .addNextIntent(webxdcIntent)
-        .getIntents();
-  }
 
   @Override
   protected boolean immersiveMode() {
@@ -554,7 +543,7 @@ public class WebxdcActivity extends WebViewActivity implements DcEventCenter.DcE
                   IconCompat.createWithBitmap(
                       bitmap)) // createWithAdaptiveBitmap() removes decorations but cuts out a too
               // small circle and defamiliarize the icon too much
-              .setIntents(getWebxdcIntentWithParentStack(context, msgId))
+              .setIntent(getWebxdcIntent(context, msgId, false, ""))
               .build();
 
       Toast.makeText(context, R.string.one_moment, Toast.LENGTH_SHORT).show();