Try using a less-rich but less-risky thread title in Conpherence handles

Summary: Ref T8478. This is easier than I thought, let's see if it's conspicious?

Test Plan:
  - Embedded `{Z2}` and saw "Private Correspondence".
  - Still saw normal stuff with useful participant lists/titles in all main UIs.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T8478

Differential Revision: https://secure.phabricator.com/D13220

src/applications/conpherence/phid/PhabricatorConpherenceThreadPHIDType.php

@@ -19,9 +19,7 @@ final class PhabricatorConpherenceThreadPHIDType extends PhabricatorPHIDType {
   protected function buildQueryForObjects(
     PhabricatorObjectQuery $query,
     array $phids) {
-
     return id(new ConpherenceThreadQuery())
-      ->needParticipantCache(true)
       ->withPHIDs($phids);
   }
 
@@ -33,7 +31,7 @@ final class PhabricatorConpherenceThreadPHIDType extends PhabricatorPHIDType {
     foreach ($handles as $phid => $handle) {
       $thread = $objects[$phid];
 
-      $title = $thread->getDisplayTitle($query->getViewer());
+      $title = $thread->getStaticTitle();
       $monogram = $thread->getMonogram();
 
       $handle->setName($title);

src/applications/conpherence/storage/ConpherenceThread.php

@@ -199,6 +199,23 @@ final class ConpherenceThread extends ConpherenceDAO
     return PhabricatorUser::getDefaultProfileImageURI();
   }
 
+  /**
+   * Get a thread title which doesn't require handles to be attached.
+   *
+   * This is a less rich title than @{method:getDisplayTitle}, but does not
+   * require handles to be attached. We use it to build thread handles without
+   * risking cycles or recursion while querying.
+   *
+   * @return string Lower quality human-readable title.
+   */
+  public function getStaticTitle() {
+    $title = $this->getTitle();
+    if (strlen($title)) {
+      return $title;
+    }
+
+    return pht('Private Correspondence');
+  }
 
   /**
    * Get the thread's display title for a user.