diff --git a/resources/sql/autopatches/20190127.project.01.subtype.sql b/resources/sql/autopatches/20190127.project.01.subtype.sql
new file mode 100644
index 0000000000..107f9202d4
--- /dev/null
+++ b/resources/sql/autopatches/20190127.project.01.subtype.sql
@@ -0,0 +1,2 @@
+ALTER TABLE {$NAMESPACE}_project.project
+  ADD subtype VARCHAR(64) COLLATE {$COLLATE_TEXT} NOT NULL;
diff --git a/resources/sql/autopatches/20190127.project.02.default.sql b/resources/sql/autopatches/20190127.project.02.default.sql
new file mode 100644
index 0000000000..1a74506cf7
--- /dev/null
+++ b/resources/sql/autopatches/20190127.project.02.default.sql
@@ -0,0 +1,2 @@
+UPDATE {$NAMESPACE}_project.project
+  SET subtype = 'default' WHERE subtype = '';
diff --git a/resources/sql/autopatches/20190129.project.01.spaces.php b/resources/sql/autopatches/20190129.project.01.spaces.php
new file mode 100644
index 0000000000..845b4ff25d
--- /dev/null
+++ b/resources/sql/autopatches/20190129.project.01.spaces.php
@@ -0,0 +1,18 @@
+<?php
+
+// See PHI1046. The "spacePHID" column for milestones may have fallen out of
+// sync; correct all existing values.
+
+$table = new PhabricatorProject();
+$conn = $table->establishConnection('w');
+$table_name = $table->getTableName();
+
+foreach (new LiskRawMigrationIterator($conn, $table_name) as $project_row) {
+  queryfx(
+    $conn,
+    'UPDATE %R SET spacePHID = %ns
+      WHERE parentProjectPHID = %s AND milestoneNumber IS NOT NULL',
+    $table,
+    $project_row['spacePHID'],
+    $project_row['phid']);
+}
diff --git a/scripts/mail/mail_handler.php b/scripts/mail/mail_handler.php
index 1c3c71f305..bf6f315f3a 100755
--- a/scripts/mail/mail_handler.php
+++ b/scripts/mail/mail_handler.php
@@ -55,8 +55,8 @@ foreach (array('text', 'html') as $part) {
 }
 
 $headers = $parser->getHeaders();
-$headers['subject'] = iconv_mime_decode($headers['subject'], 0, 'UTF-8');
-$headers['from'] = iconv_mime_decode($headers['from'], 0, 'UTF-8');
+$headers['subject'] = phutil_decode_mime_header($headers['subject']);
+$headers['from'] = phutil_decode_mime_header($headers['from']);
 
 if ($args->getArg('process-duplicates')) {
   $headers['message-id'] = Filesystem::readRandomCharacters(64);
diff --git a/src/__phutil_library_map__.php b/src/__phutil_library_map__.php
index c5723894d5..324fc3c5de 100644
--- a/src/__phutil_library_map__.php
+++ b/src/__phutil_library_map__.php
@@ -183,7 +183,6 @@ phutil_register_library_map(array(
     'AphrontCalendarEventView' => 'applications/calendar/view/AphrontCalendarEventView.php',
     'AphrontController' => 'aphront/AphrontController.php',
     'AphrontCursorPagerView' => 'view/control/AphrontCursorPagerView.php',
-    'AphrontDefaultApplicationConfiguration' => 'aphront/configuration/AphrontDefaultApplicationConfiguration.php',
     'AphrontDialogResponse' => 'aphront/response/AphrontDialogResponse.php',
     'AphrontDialogView' => 'view/AphrontDialogView.php',
     'AphrontEpochHTTPParameterType' => 'aphront/httpparametertype/AphrontEpochHTTPParameterType.php',
@@ -2235,8 +2234,10 @@ phutil_register_library_map(array(
     'PhabricatorAuthFactorProviderEditController' => 'applications/auth/controller/mfa/PhabricatorAuthFactorProviderEditController.php',
     'PhabricatorAuthFactorProviderEditEngine' => 'applications/auth/editor/PhabricatorAuthFactorProviderEditEngine.php',
     'PhabricatorAuthFactorProviderEditor' => 'applications/auth/editor/PhabricatorAuthFactorProviderEditor.php',
+    'PhabricatorAuthFactorProviderEnrollMessageTransaction' => 'applications/auth/xaction/PhabricatorAuthFactorProviderEnrollMessageTransaction.php',
     'PhabricatorAuthFactorProviderListController' => 'applications/auth/controller/mfa/PhabricatorAuthFactorProviderListController.php',
     'PhabricatorAuthFactorProviderMFAEngine' => 'applications/auth/engine/PhabricatorAuthFactorProviderMFAEngine.php',
+    'PhabricatorAuthFactorProviderMessageController' => 'applications/auth/controller/mfa/PhabricatorAuthFactorProviderMessageController.php',
     'PhabricatorAuthFactorProviderNameTransaction' => 'applications/auth/xaction/PhabricatorAuthFactorProviderNameTransaction.php',
     'PhabricatorAuthFactorProviderQuery' => 'applications/auth/query/PhabricatorAuthFactorProviderQuery.php',
     'PhabricatorAuthFactorProviderStatus' => 'applications/auth/constants/PhabricatorAuthFactorProviderStatus.php',
@@ -3061,6 +3062,8 @@ phutil_register_library_map(array(
     'PhabricatorEditPage' => 'applications/transactions/editengine/PhabricatorEditPage.php',
     'PhabricatorEditType' => 'applications/transactions/edittype/PhabricatorEditType.php',
     'PhabricatorEditor' => 'infrastructure/PhabricatorEditor.php',
+    'PhabricatorEditorExtension' => 'applications/transactions/engineextension/PhabricatorEditorExtension.php',
+    'PhabricatorEditorExtensionModule' => 'applications/transactions/engineextension/PhabricatorEditorExtensionModule.php',
     'PhabricatorEditorMailEngineExtension' => 'applications/transactions/engineextension/PhabricatorEditorMailEngineExtension.php',
     'PhabricatorEditorMultipleSetting' => 'applications/settings/setting/PhabricatorEditorMultipleSetting.php',
     'PhabricatorEditorSetting' => 'applications/settings/setting/PhabricatorEditorSetting.php',
@@ -4114,6 +4117,8 @@ phutil_register_library_map(array(
     'PhabricatorProjectSubprojectWarningController' => 'applications/project/controller/PhabricatorProjectSubprojectWarningController.php',
     'PhabricatorProjectSubprojectsController' => 'applications/project/controller/PhabricatorProjectSubprojectsController.php',
     'PhabricatorProjectSubprojectsProfileMenuItem' => 'applications/project/menuitem/PhabricatorProjectSubprojectsProfileMenuItem.php',
+    'PhabricatorProjectSubtypeDatasource' => 'applications/project/typeahead/PhabricatorProjectSubtypeDatasource.php',
+    'PhabricatorProjectSubtypesConfigType' => 'applications/project/config/PhabricatorProjectSubtypesConfigType.php',
     'PhabricatorProjectTestDataGenerator' => 'applications/project/lipsum/PhabricatorProjectTestDataGenerator.php',
     'PhabricatorProjectTransaction' => 'applications/project/storage/PhabricatorProjectTransaction.php',
     'PhabricatorProjectTransactionEditor' => 'applications/project/editor/PhabricatorProjectTransactionEditor.php',
@@ -5625,7 +5630,6 @@ phutil_register_library_map(array(
     'AphrontCalendarEventView' => 'AphrontView',
     'AphrontController' => 'Phobject',
     'AphrontCursorPagerView' => 'AphrontView',
-    'AphrontDefaultApplicationConfiguration' => 'AphrontApplicationConfiguration',
     'AphrontDialogResponse' => 'AphrontResponse',
     'AphrontDialogView' => array(
       'AphrontView',
@@ -7971,8 +7975,10 @@ phutil_register_library_map(array(
     'PhabricatorAuthFactorProviderEditController' => 'PhabricatorAuthFactorProviderController',
     'PhabricatorAuthFactorProviderEditEngine' => 'PhabricatorEditEngine',
     'PhabricatorAuthFactorProviderEditor' => 'PhabricatorApplicationTransactionEditor',
+    'PhabricatorAuthFactorProviderEnrollMessageTransaction' => 'PhabricatorAuthFactorProviderTransactionType',
     'PhabricatorAuthFactorProviderListController' => 'PhabricatorAuthProviderController',
     'PhabricatorAuthFactorProviderMFAEngine' => 'PhabricatorEditEngineMFAEngine',
+    'PhabricatorAuthFactorProviderMessageController' => 'PhabricatorAuthFactorProviderController',
     'PhabricatorAuthFactorProviderNameTransaction' => 'PhabricatorAuthFactorProviderTransactionType',
     'PhabricatorAuthFactorProviderQuery' => 'PhabricatorCursorPagedPolicyAwareQuery',
     'PhabricatorAuthFactorProviderStatus' => 'Phobject',
@@ -8925,6 +8931,8 @@ phutil_register_library_map(array(
     'PhabricatorEditPage' => 'Phobject',
     'PhabricatorEditType' => 'Phobject',
     'PhabricatorEditor' => 'Phobject',
+    'PhabricatorEditorExtension' => 'Phobject',
+    'PhabricatorEditorExtensionModule' => 'PhabricatorConfigModule',
     'PhabricatorEditorMailEngineExtension' => 'PhabricatorMailEngineExtension',
     'PhabricatorEditorMultipleSetting' => 'PhabricatorSelectSetting',
     'PhabricatorEditorSetting' => 'PhabricatorStringSetting',
@@ -10029,6 +10037,7 @@ phutil_register_library_map(array(
       'PhabricatorConduitResultInterface',
       'PhabricatorColumnProxyInterface',
       'PhabricatorSpacesInterface',
+      'PhabricatorEditEngineSubtypeInterface',
     ),
     'PhabricatorProjectAddHeraldAction' => 'PhabricatorProjectHeraldAction',
     'PhabricatorProjectApplication' => 'PhabricatorApplication',
@@ -10156,6 +10165,8 @@ phutil_register_library_map(array(
     'PhabricatorProjectSubprojectWarningController' => 'PhabricatorProjectController',
     'PhabricatorProjectSubprojectsController' => 'PhabricatorProjectController',
     'PhabricatorProjectSubprojectsProfileMenuItem' => 'PhabricatorProfileMenuItem',
+    'PhabricatorProjectSubtypeDatasource' => 'PhabricatorTypeaheadDatasource',
+    'PhabricatorProjectSubtypesConfigType' => 'PhabricatorJSONConfigType',
     'PhabricatorProjectTestDataGenerator' => 'PhabricatorTestDataGenerator',
     'PhabricatorProjectTransaction' => 'PhabricatorModularTransaction',
     'PhabricatorProjectTransactionEditor' => 'PhabricatorApplicationTransactionEditor',
diff --git a/src/aphront/configuration/AphrontApplicationConfiguration.php b/src/aphront/configuration/AphrontApplicationConfiguration.php
index 60b12557c9..8d36bbc880 100644
--- a/src/aphront/configuration/AphrontApplicationConfiguration.php
+++ b/src/aphront/configuration/AphrontApplicationConfiguration.php
@@ -5,55 +5,81 @@
  * @task response Response Handling
  * @task exception Exception Handling
  */
-abstract class AphrontApplicationConfiguration extends Phobject {
+final class AphrontApplicationConfiguration
+  extends Phobject {
 
   private $request;
   private $host;
   private $path;
   private $console;
 
-  abstract public function buildRequest();
-  abstract public function build404Controller();
-  abstract public function buildRedirectController($uri, $external);
+  public function buildRequest() {
+    $parser = new PhutilQueryStringParser();
 
-  final public function setRequest(AphrontRequest $request) {
+    $data = array();
+    $data += $_POST;
+    $data += $parser->parseQueryString(idx($_SERVER, 'QUERY_STRING', ''));
+
+    $cookie_prefix = PhabricatorEnv::getEnvConfig('phabricator.cookie-prefix');
+
+    $request = new AphrontRequest($this->getHost(), $this->getPath());
+    $request->setRequestData($data);
+    $request->setApplicationConfiguration($this);
+    $request->setCookiePrefix($cookie_prefix);
+
+    return $request;
+  }
+
+  public function build404Controller() {
+    return array(new Phabricator404Controller(), array());
+  }
+
+  public function buildRedirectController($uri, $external) {
+    return array(
+      new PhabricatorRedirectController(),
+      array(
+        'uri' => $uri,
+        'external' => $external,
+      ),
+    );
+  }
+
+  public function setRequest(AphrontRequest $request) {
     $this->request = $request;
     return $this;
   }
 
-  final public function getRequest() {
+  public function getRequest() {
     return $this->request;
   }
 
-  final public function getConsole() {
+  public function getConsole() {
     return $this->console;
   }
 
-  final public function setConsole($console) {
+  public function setConsole($console) {
     $this->console = $console;
     return $this;
   }
 
-  final public function setHost($host) {
+  public function setHost($host) {
     $this->host = $host;
     return $this;
   }
 
-  final public function getHost() {
+  public function getHost() {
     return $this->host;
   }
 
-  final public function setPath($path) {
+  public function setPath($path) {
     $this->path = $path;
     return $this;
   }
 
-  final public function getPath() {
+  public function getPath() {
     return $this->path;
   }
 
-  public function willBuildRequest() {}
-
 
   /**
    * @phutil-external-symbol class PhabricatorStartup
@@ -83,6 +109,8 @@ abstract class AphrontApplicationConfiguration extends Phobject {
 
     PhabricatorStartup::beginStartupPhase('env.init');
 
+    self::readHTTPPOSTData();
+
     try {
       PhabricatorEnv::initializeWebEnvironment();
       $database_exception = null;
@@ -142,16 +170,10 @@ abstract class AphrontApplicationConfiguration extends Phobject {
     $host = AphrontRequest::getHTTPHeader('Host');
     $path = $_REQUEST['__path__'];
 
-    switch ($host) {
-      default:
-        $config_key = 'aphront.default-application-configuration-class';
-        $application = PhabricatorEnv::newObjectFromConfig($config_key);
-        break;
-    }
+    $application = new self();
 
     $application->setHost($host);
     $application->setPath($path);
-    $application->willBuildRequest();
     $request = $application->buildRequest();
 
     // Now that we have a request, convert the write guard into one which
@@ -313,7 +335,7 @@ abstract class AphrontApplicationConfiguration extends Phobject {
    *                                      parameters.
    * @task routing
    */
-  final private function buildController() {
+  private function buildController() {
     $request = $this->getRequest();
 
     // If we're configured to operate in cluster mode, reject requests which
@@ -708,4 +730,88 @@ abstract class AphrontApplicationConfiguration extends Phobject {
       ->setContent($result);
   }
 
+  private static function readHTTPPOSTData() {
+    $request_method = idx($_SERVER, 'REQUEST_METHOD');
+    if ($request_method === 'PUT') {
+      // For PUT requests, do nothing: in particular, do NOT read input. This
+      // allows us to stream input later and process very large PUT requests,
+      // like those coming from Git LFS.
+      return;
+    }
+
+
+    // For POST requests, we're going to read the raw input ourselves here
+    // if we can. Among other things, this corrects variable names with
+    // the "." character in them, which PHP normally converts into "_".
+
+    // There are two major considerations here: whether the
+    // `enable_post_data_reading` option is set, and whether the content
+    // type is "multipart/form-data" or not.
+
+    // If `enable_post_data_reading` is off, we're free to read the entire
+    // raw request body and parse it -- and we must, because $_POST and
+    // $_FILES are not built for us. If `enable_post_data_reading` is on,
+    // which is the default, we may not be able to read the body (the
+    // documentation says we can't, but empirically we can at least some
+    // of the time).
+
+    // If the content type is "multipart/form-data", we need to build both
+    // $_POST and $_FILES, which is involved. The body itself is also more
+    // difficult to parse than other requests.
+    $raw_input = PhabricatorStartup::getRawInput();
+    $parser = new PhutilQueryStringParser();
+
+    if (strlen($raw_input)) {
+      $content_type = idx($_SERVER, 'CONTENT_TYPE');
+      $is_multipart = preg_match('@^multipart/form-data@i', $content_type);
+      if ($is_multipart && !ini_get('enable_post_data_reading')) {
+        $multipart_parser = id(new AphrontMultipartParser())
+          ->setContentType($content_type);
+
+        $multipart_parser->beginParse();
+        $multipart_parser->continueParse($raw_input);
+        $parts = $multipart_parser->endParse();
+
+        // We're building and then parsing a query string so that requests
+        // with arrays (like "x[]=apple&x[]=banana") work correctly. This also
+        // means we can't use "phutil_build_http_querystring()", since it
+        // can't build a query string with duplicate names.
+
+        $query_string = array();
+        foreach ($parts as $part) {
+          if (!$part->isVariable()) {
+            continue;
+          }
+
+          $name = $part->getName();
+          $value = $part->getVariableValue();
+          $query_string[] = rawurlencode($name).'='.rawurlencode($value);
+        }
+        $query_string = implode('&', $query_string);
+        $post = $parser->parseQueryString($query_string);
+
+        $files = array();
+        foreach ($parts as $part) {
+          if ($part->isVariable()) {
+            continue;
+          }
+
+          $files[$part->getName()] = $part->getPHPFileDictionary();
+        }
+        $_FILES = $files;
+      } else {
+        $post = $parser->parseQueryString($raw_input);
+      }
+
+      $_POST = $post;
+      PhabricatorStartup::rebuildRequest();
+    } else if ($_POST) {
+      $post = filter_input_array(INPUT_POST, FILTER_UNSAFE_RAW);
+      if (is_array($post)) {
+        $_POST = $post;
+        PhabricatorStartup::rebuildRequest();
+      }
+    }
+  }
+
 }
diff --git a/src/aphront/configuration/AphrontDefaultApplicationConfiguration.php b/src/aphront/configuration/AphrontDefaultApplicationConfiguration.php
deleted file mode 100644
index fb67919576..0000000000
--- a/src/aphront/configuration/AphrontDefaultApplicationConfiguration.php
+++ /dev/null
@@ -1,121 +0,0 @@
-<?php
-
-/**
- * NOTE: Do not extend this!
- *
- * @concrete-extensible
- */
-class AphrontDefaultApplicationConfiguration
-  extends AphrontApplicationConfiguration {
-
-  /**
-   * @phutil-external-symbol class PhabricatorStartup
-   */
-  public function buildRequest() {
-    $parser = new PhutilQueryStringParser();
-    $data   = array();
-
-    $request_method = idx($_SERVER, 'REQUEST_METHOD');
-    if ($request_method === 'PUT') {
-      // For PUT requests, do nothing: in particular, do NOT read input. This
-      // allows us to stream input later and process very large PUT requests,
-      // like those coming from Git LFS.
-    } else {
-      // For POST requests, we're going to read the raw input ourselves here
-      // if we can. Among other things, this corrects variable names with
-      // the "." character in them, which PHP normally converts into "_".
-
-      // There are two major considerations here: whether the
-      // `enable_post_data_reading` option is set, and whether the content
-      // type is "multipart/form-data" or not.
-
-      // If `enable_post_data_reading` is off, we're free to read the entire
-      // raw request body and parse it -- and we must, because $_POST and
-      // $_FILES are not built for us. If `enable_post_data_reading` is on,
-      // which is the default, we may not be able to read the body (the
-      // documentation says we can't, but empirically we can at least some
-      // of the time).
-
-      // If the content type is "multipart/form-data", we need to build both
-      // $_POST and $_FILES, which is involved. The body itself is also more
-      // difficult to parse than other requests.
-      $raw_input = PhabricatorStartup::getRawInput();
-      if (strlen($raw_input)) {
-        $content_type = idx($_SERVER, 'CONTENT_TYPE');
-        $is_multipart = preg_match('@^multipart/form-data@i', $content_type);
-        if ($is_multipart && !ini_get('enable_post_data_reading')) {
-          $multipart_parser = id(new AphrontMultipartParser())
-            ->setContentType($content_type);
-
-          $multipart_parser->beginParse();
-          $multipart_parser->continueParse($raw_input);
-          $parts = $multipart_parser->endParse();
-
-          $query_string = array();
-          foreach ($parts as $part) {
-            if (!$part->isVariable()) {
-              continue;
-            }
-
-            $name = $part->getName();
-            $value = $part->getVariableValue();
-
-            $query_string[] = urlencode($name).'='.urlencode($value);
-          }
-          $query_string = implode('&', $query_string);
-          $post = $parser->parseQueryString($query_string);
-
-          $files = array();
-          foreach ($parts as $part) {
-            if ($part->isVariable()) {
-              continue;
-            }
-
-            $files[$part->getName()] = $part->getPHPFileDictionary();
-          }
-          $_FILES = $files;
-        } else {
-          $post = $parser->parseQueryString($raw_input);
-        }
-
-        $_POST = $post;
-        PhabricatorStartup::rebuildRequest();
-
-        $data += $post;
-      } else if ($_POST) {
-        $post = filter_input_array(INPUT_POST, FILTER_UNSAFE_RAW);
-        if (is_array($post)) {
-          $_POST = $post;
-          PhabricatorStartup::rebuildRequest();
-        }
-        $data += $_POST;
-      }
-    }
-
-    $data += $parser->parseQueryString(idx($_SERVER, 'QUERY_STRING', ''));
-
-    $cookie_prefix = PhabricatorEnv::getEnvConfig('phabricator.cookie-prefix');
-
-    $request = new AphrontRequest($this->getHost(), $this->getPath());
-    $request->setRequestData($data);
-    $request->setApplicationConfiguration($this);
-    $request->setCookiePrefix($cookie_prefix);
-
-    return $request;
-  }
-
-  public function build404Controller() {
-    return array(new Phabricator404Controller(), array());
-  }
-
-  public function buildRedirectController($uri, $external) {
-    return array(
-      new PhabricatorRedirectController(),
-      array(
-        'uri' => $uri,
-        'external' => $external,
-      ),
-    );
-  }
-
-}
diff --git a/src/aphront/handler/PhabricatorHighSecurityRequestExceptionHandler.php b/src/aphront/handler/PhabricatorHighSecurityRequestExceptionHandler.php
index 2a737ecf5c..7f4eddad45 100644
--- a/src/aphront/handler/PhabricatorHighSecurityRequestExceptionHandler.php
+++ b/src/aphront/handler/PhabricatorHighSecurityRequestExceptionHandler.php
@@ -78,15 +78,13 @@ final class PhabricatorHighSecurityRequestExceptionHandler
     $form_layout = $form->buildLayoutView();
 
     if ($is_upgrade) {
-      $messages = array(
-        pht(
-          'You are taking an action which requires you to enter '.
-          'high security.'),
-      );
+      $message = pht(
+        'You are taking an action which requires you to enter '.
+        'high security.');
 
       $info_view = id(new PHUIInfoView())
         ->setSeverity(PHUIInfoView::SEVERITY_MFA)
-        ->setErrors($messages);
+        ->setErrors(array($message));
 
       $dialog
         ->appendChild($info_view)
@@ -100,12 +98,18 @@ final class PhabricatorHighSecurityRequestExceptionHandler
             'period of time. When you are finished taking sensitive '.
             'actions, you should leave high security.'));
     } else {
+      $message = pht(
+        'You are taking an action which requires you to provide '.
+        'multi-factor credentials.');
+
+      $info_view = id(new PHUIInfoView())
+        ->setSeverity(PHUIInfoView::SEVERITY_MFA)
+        ->setErrors(array($message));
+
       $dialog
+        ->appendChild($info_view)
         ->setErrors(
           array(
-            pht(
-              'You are taking an action which requires you to provide '.
-              'multi-factor credentials.'),
           ))
         ->appendChild($form_layout);
     }
diff --git a/src/applications/auth/application/PhabricatorAuthApplication.php b/src/applications/auth/application/PhabricatorAuthApplication.php
index a9ab3be181..df86595b46 100644
--- a/src/applications/auth/application/PhabricatorAuthApplication.php
+++ b/src/applications/auth/application/PhabricatorAuthApplication.php
@@ -95,6 +95,8 @@ final class PhabricatorAuthApplication extends PhabricatorApplication {
             'PhabricatorAuthFactorProviderEditController',
           '(?P<id>[1-9]\d*)/' =>
             'PhabricatorAuthFactorProviderViewController',
+          'message/(?P<id>[1-9]\d*)/' =>
+            'PhabricatorAuthFactorProviderMessageController',
         ),
 
         'message/' => array(
diff --git a/src/applications/auth/controller/mfa/PhabricatorAuthFactorProviderMessageController.php b/src/applications/auth/controller/mfa/PhabricatorAuthFactorProviderMessageController.php
new file mode 100644
index 0000000000..563ee39931
--- /dev/null
+++ b/src/applications/auth/controller/mfa/PhabricatorAuthFactorProviderMessageController.php
@@ -0,0 +1,84 @@
+<?php
+
+final class PhabricatorAuthFactorProviderMessageController
+  extends PhabricatorAuthFactorProviderController {
+
+  public function handleRequest(AphrontRequest $request) {
+    $this->requireApplicationCapability(
+      AuthManageProvidersCapability::CAPABILITY);
+
+    $viewer = $request->getViewer();
+    $id = $request->getURIData('id');
+
+    $provider = id(new PhabricatorAuthFactorProviderQuery())
+      ->setViewer($viewer)
+      ->withIDs(array($id))
+      ->requireCapabilities(
+        array(
+          PhabricatorPolicyCapability::CAN_VIEW,
+          PhabricatorPolicyCapability::CAN_EDIT,
+        ))
+      ->executeOne();
+    if (!$provider) {
+      return new Aphront404Response();
+    }
+
+    $cancel_uri = $provider->getURI();
+    $enroll_key =
+      PhabricatorAuthFactorProviderEnrollMessageTransaction::TRANSACTIONTYPE;
+
+    $message = $provider->getEnrollMessage();
+
+    if ($request->isFormOrHisecPost()) {
+      $message = $request->getStr('message');
+
+      $xactions = array();
+
+      $xactions[] = id(new PhabricatorAuthFactorProviderTransaction())
+        ->setTransactionType($enroll_key)
+        ->setNewValue($message);
+
+      $editor = id(new PhabricatorAuthFactorProviderEditor())
+        ->setActor($viewer)
+        ->setContentSourceFromRequest($request)
+        ->setContinueOnNoEffect(true)
+        ->setContinueOnMissingFields(true)
+        ->setCancelURI($cancel_uri);
+
+      $editor->applyTransactions($provider, $xactions);
+
+      return id(new AphrontRedirectResponse())->setURI($cancel_uri);
+    }
+
+    $default_message = $provider->getEnrollDescription($viewer);
+    $default_message = new PHUIRemarkupView($viewer, $default_message);
+
+    $form = id(new AphrontFormView())
+      ->setViewer($viewer)
+      ->appendRemarkupInstructions(
+        pht(
+          'When users add a factor for this provider, they are given this '.
+          'enrollment guidance by default:'))
+      ->appendControl(
+        id(new AphrontFormMarkupControl())
+          ->setLabel(pht('Default Message'))
+          ->setValue($default_message))
+      ->appendRemarkupInstructions(
+        pht(
+          'You may optionally customize the enrollment message users are '.
+          'presented with by providing a replacement message below:'))
+      ->appendControl(
+        id(new PhabricatorRemarkupControl())
+          ->setLabel(pht('Custom Message'))
+          ->setName('message')
+          ->setValue($message));
+
+    return $this->newDialog()
+      ->setTitle(pht('Change Enroll Message'))
+      ->setWidth(AphrontDialogView::WIDTH_FORM)
+      ->appendForm($form)
+      ->addCancelButton($cancel_uri)
+      ->addSubmitButton(pht('Save'));
+  }
+
+}
diff --git a/src/applications/auth/controller/mfa/PhabricatorAuthFactorProviderViewController.php b/src/applications/auth/controller/mfa/PhabricatorAuthFactorProviderViewController.php
index 3047c8714d..1dac49bcf9 100644
--- a/src/applications/auth/controller/mfa/PhabricatorAuthFactorProviderViewController.php
+++ b/src/applications/auth/controller/mfa/PhabricatorAuthFactorProviderViewController.php
@@ -81,6 +81,16 @@ final class PhabricatorAuthFactorProviderViewController
       pht('Factor Type'),
       $provider->getFactor()->getFactorName());
 
+
+    $custom_enroll = $provider->getEnrollMessage();
+    if (strlen($custom_enroll)) {
+      $view->addSectionHeader(
+        pht('Custom Enroll Message'),
+        PHUIPropertyListView::ICON_SUMMARY);
+      $view->addTextContent(
+        new PHUIRemarkupView($viewer, $custom_enroll));
+    }
+
     return $view;
   }
 
@@ -103,6 +113,14 @@ final class PhabricatorAuthFactorProviderViewController
         ->setDisabled(!$can_edit)
         ->setWorkflow(!$can_edit));
 
+    $curtain->addAction(
+      id(new PhabricatorActionView())
+        ->setName(pht('Customize Enroll Message'))
+        ->setIcon('fa-commenting-o')
+        ->setHref($this->getApplicationURI("mfa/message/{$id}/"))
+        ->setDisabled(!$can_edit)
+        ->setWorkflow(true));
+
     return $curtain;
   }
 
diff --git a/src/applications/auth/factor/PhabricatorAuthFactor.php b/src/applications/auth/factor/PhabricatorAuthFactor.php
index 345ace3df9..ec49f7f748 100644
--- a/src/applications/auth/factor/PhabricatorAuthFactor.php
+++ b/src/applications/auth/factor/PhabricatorAuthFactor.php
@@ -147,7 +147,7 @@ abstract class PhabricatorAuthFactor extends Phobject {
       $viewer,
       $challenges);
 
-    if ($new_challenges instanceof PhabricatorAuthFactorResult) {
+    if ($this->isAuthResult($new_challenges)) {
       unset($unguarded);
       return $new_challenges;
     }
@@ -200,7 +200,7 @@ abstract class PhabricatorAuthFactor extends Phobject {
       return $result;
     }
 
-    if (!($result instanceof PhabricatorAuthFactorResult)) {
+    if (!$this->isAuthResult($result)) {
       throw new Exception(
         pht(
           'Expected "newResultFromIssuedChallenges()" to return null or '.
@@ -232,7 +232,7 @@ abstract class PhabricatorAuthFactor extends Phobject {
       $request,
       $challenges);
 
-    if (!($result instanceof PhabricatorAuthFactorResult)) {
+    if (!$this->isAuthResult($result)) {
       throw new Exception(
         pht(
           'Expected "newResultFromChallengeResponse()" to return an object '.
@@ -408,6 +408,10 @@ abstract class PhabricatorAuthFactor extends Phobject {
         $provider,
         $user);
 
+      if ($this->isAuthResult($properties)) {
+        return $properties;
+      }
+
       foreach ($properties as $key => $value) {
         $sync_token->setTemporaryTokenProperty($key, $value);
       }
@@ -555,4 +559,8 @@ abstract class PhabricatorAuthFactor extends Phobject {
       ->execute();
   }
 
+  final protected function isAuthResult($object) {
+    return ($object instanceof PhabricatorAuthFactorResult);
+  }
+
 }
diff --git a/src/applications/auth/factor/PhabricatorDuoAuthFactor.php b/src/applications/auth/factor/PhabricatorDuoAuthFactor.php
index f5e2455c79..187e011953 100644
--- a/src/applications/auth/factor/PhabricatorDuoAuthFactor.php
+++ b/src/applications/auth/factor/PhabricatorDuoAuthFactor.php
@@ -157,6 +157,10 @@ final class PhabricatorDuoAuthFactor
     PhabricatorUser $user) {
 
     $token = $this->loadMFASyncToken($provider, $request, $form, $user);
+    if ($this->isAuthResult($token)) {
+      $form->appendChild($this->newAutomaticControl($token));
+      return;
+    }
 
     $enroll = $token->getTemporaryTokenProperty('duo.enroll');
     $duo_id = $token->getTemporaryTokenProperty('duo.user-id');
@@ -350,6 +354,7 @@ final class PhabricatorDuoAuthFactor
 
     $external_uri = null;
     $result_code = $result['response']['result'];
+    $status_message = $result['response']['status_msg'];
     switch ($result_code) {
       case 'auth':
       case 'allow':
@@ -376,7 +381,13 @@ final class PhabricatorDuoAuthFactor
         return $this->newResult()
           ->setIsError(true)
           ->setErrorMessage(
-            pht('Your account is not permitted to access this system.'));
+            pht(
+              'Your Duo account ("%s") is not permitted to access this '.
+              'system. Contact your Duo administrator for help. '.
+              'The Duo preauth API responded with status message ("%s"): %s',
+              $duo_user,
+              $result_code,
+              $status_message));
     }
 
     // Duo's "/enroll" API isn't repeatable for the same username. If we're
@@ -476,7 +487,10 @@ final class PhabricatorDuoAuthFactor
           ->setIsError(true)
           ->setErrorMessage(
             pht(
-              'Duo has denied you access. Duo status message ("%s"): %s',
+              'Your Duo account ("%s") is not permitted to access this '.
+              'system. Contact your Duo administrator for help. The Duo '.
+              'preauth API responded with status message ("%s"): %s',
+              $duo_user,
               $next_step,
               $status_message));
     }
@@ -504,10 +518,7 @@ final class PhabricatorDuoAuthFactor
     $push_info = array(
       pht('Domain') => $this->getInstallDisplayName(),
     );
-    foreach ($push_info as $k => $v) {
-      $push_info[$k] = rawurlencode($k).'='.rawurlencode($v);
-    }
-    $push_info = implode('&', $push_info);
+    $push_info = phutil_build_http_querystring($push_info);
 
     $parameters = array(
       'username' => $duo_user,
diff --git a/src/applications/auth/future/PhabricatorDuoFuture.php b/src/applications/auth/future/PhabricatorDuoFuture.php
index fd95906da1..81a5a2a2b8 100644
--- a/src/applications/auth/future/PhabricatorDuoFuture.php
+++ b/src/applications/auth/future/PhabricatorDuoFuture.php
@@ -91,11 +91,7 @@ final class PhabricatorDuoFuture
       $http_method = $this->getHTTPMethod();
 
       ksort($data);
-      $data_parts = array();
-      foreach ($data as $key => $value) {
-        $data_parts[] = rawurlencode($key).'='.rawurlencode($value);
-      }
-      $data_parts = implode('&', $data_parts);
+      $data_parts = phutil_build_http_querystring($data);
 
       $corpus = array(
         $date,
diff --git a/src/applications/auth/storage/PhabricatorAuthFactorProvider.php b/src/applications/auth/storage/PhabricatorAuthFactorProvider.php
index 79acd4f23e..2213535dff 100644
--- a/src/applications/auth/storage/PhabricatorAuthFactorProvider.php
+++ b/src/applications/auth/storage/PhabricatorAuthFactorProvider.php
@@ -57,6 +57,14 @@ final class PhabricatorAuthFactorProvider
     return $this;
   }
 
+  public function getEnrollMessage() {
+    return $this->getAuthFactorProviderProperty('enroll-message');
+  }
+
+  public function setEnrollMessage($message) {
+    return $this->setAuthFactorProviderProperty('enroll-message', $message);
+  }
+
   public function attachFactor(PhabricatorAuthFactor $factor) {
     $this->factor = $factor;
     return $this;
diff --git a/src/applications/auth/xaction/PhabricatorAuthFactorProviderEnrollMessageTransaction.php b/src/applications/auth/xaction/PhabricatorAuthFactorProviderEnrollMessageTransaction.php
new file mode 100644
index 0000000000..d6d26143c1
--- /dev/null
+++ b/src/applications/auth/xaction/PhabricatorAuthFactorProviderEnrollMessageTransaction.php
@@ -0,0 +1,39 @@
+<?php
+
+final class PhabricatorAuthFactorProviderEnrollMessageTransaction
+  extends PhabricatorAuthFactorProviderTransactionType {
+
+  const TRANSACTIONTYPE = 'enroll-message';
+
+  public function generateOldValue($object) {
+    return $object->getEnrollMessage();
+  }
+
+  public function applyInternalEffects($object, $value) {
+    $object->setEnrollMessage($value);
+  }
+
+  public function getTitle() {
+    return pht(
+      '%s updated the enroll message.',
+      $this->renderAuthor());
+  }
+
+  public function hasChangeDetailView() {
+    return true;
+  }
+
+  public function getMailDiffSectionHeader() {
+    return pht('CHANGES TO ENROLL MESSAGE');
+  }
+
+  public function newChangeDetailView() {
+    $viewer = $this->getViewer();
+
+    return id(new PhabricatorApplicationTransactionTextDiffDetailView())
+      ->setViewer($viewer)
+      ->setOldText($this->getOldValue())
+      ->setNewText($this->getNewValue());
+  }
+
+}
diff --git a/src/applications/base/controller/__tests__/PhabricatorAccessControlTestCase.php b/src/applications/base/controller/__tests__/PhabricatorAccessControlTestCase.php
index 98fa948722..7d763d6e64 100644
--- a/src/applications/base/controller/__tests__/PhabricatorAccessControlTestCase.php
+++ b/src/applications/base/controller/__tests__/PhabricatorAccessControlTestCase.php
@@ -12,7 +12,7 @@ final class PhabricatorAccessControlTestCase extends PhabricatorTestCase {
     $root = dirname(phutil_get_library_root('phabricator'));
     require_once $root.'/support/startup/PhabricatorStartup.php';
 
-    $application_configuration = new AphrontDefaultApplicationConfiguration();
+    $application_configuration = new AphrontApplicationConfiguration();
 
     $host = 'meow.example.com';
 
diff --git a/src/applications/config/check/PhabricatorExtensionsSetupCheck.php b/src/applications/config/check/PhabricatorExtensionsSetupCheck.php
index 973c80629b..51105de1c5 100644
--- a/src/applications/config/check/PhabricatorExtensionsSetupCheck.php
+++ b/src/applications/config/check/PhabricatorExtensionsSetupCheck.php
@@ -11,14 +11,13 @@ final class PhabricatorExtensionsSetupCheck extends PhabricatorSetupCheck {
   }
 
   protected function executeChecks() {
-    // TODO: Make 'mbstring' and 'iconv' soft requirements.
+    // TODO: Make 'mbstring' a soft requirement.
 
     $required = array(
       'hash',
       'json',
       'openssl',
       'mbstring',
-      'iconv',
       'ctype',
 
       // There is a tiny chance we might not need this, but a significant
diff --git a/src/applications/config/check/PhabricatorExtraConfigSetupCheck.php b/src/applications/config/check/PhabricatorExtraConfigSetupCheck.php
index d5f44c87c8..1c8a593a78 100644
--- a/src/applications/config/check/PhabricatorExtraConfigSetupCheck.php
+++ b/src/applications/config/check/PhabricatorExtraConfigSetupCheck.php
@@ -416,6 +416,10 @@ final class PhabricatorExtraConfigSetupCheck extends PhabricatorSetupCheck {
       'metamta.pholio.subject-prefix' => $prefix_reason,
       'metamta.phriction.subject-prefix' => $prefix_reason,
 
+      'aphront.default-application-configuration-class' => pht(
+        'This ancient extension point has been replaced with other '.
+        'mechanisms, including "AphrontSite".'),
+
     );
 
     return $ancient_config;
diff --git a/src/applications/config/controller/PhabricatorConfigVersionController.php b/src/applications/config/controller/PhabricatorConfigVersionController.php
index 8a87dec5cc..a9571a1f85 100644
--- a/src/applications/config/controller/PhabricatorConfigVersionController.php
+++ b/src/applications/config/controller/PhabricatorConfigVersionController.php
@@ -63,6 +63,8 @@ final class PhabricatorConfigVersionController
         $version_from_file);
     }
 
+    $version_property_list->addProperty('php', phpversion());
+
     $binaries = PhutilBinaryAnalyzer::getAllBinaries();
     foreach ($binaries as $binary) {
       if (!$binary->isBinaryAvailable()) {
diff --git a/src/applications/config/option/PhabricatorExtendingPhabricatorConfigOptions.php b/src/applications/config/option/PhabricatorExtendingPhabricatorConfigOptions.php
index 28a0f619dd..0a3ea32e44 100644
--- a/src/applications/config/option/PhabricatorExtendingPhabricatorConfigOptions.php
+++ b/src/applications/config/option/PhabricatorExtendingPhabricatorConfigOptions.php
@@ -36,14 +36,6 @@ final class PhabricatorExtendingPhabricatorConfigOptions
             'occur. Specify a list of classes which extend '.
             'PhabricatorEventListener here.'))
         ->addExample('MyEventListener', pht('Valid Setting')),
-       $this->newOption(
-         'aphront.default-application-configuration-class',
-         'class',
-         'AphrontDefaultApplicationConfiguration')
-        ->setLocked(true)
-        ->setBaseClass('AphrontApplicationConfiguration')
-        // TODO: This could probably use some better documentation.
-        ->setDescription(pht('Application configuration class.')),
     );
   }
 
diff --git a/src/applications/differential/editor/DifferentialRevisionEditEngine.php b/src/applications/differential/editor/DifferentialRevisionEditEngine.php
index 07b693044f..9c399036d5 100644
--- a/src/applications/differential/editor/DifferentialRevisionEditEngine.php
+++ b/src/applications/differential/editor/DifferentialRevisionEditEngine.php
@@ -235,6 +235,32 @@ final class DifferentialRevisionEditEngine
       ->setConduitTypeDescription(pht('List of tasks.'))
       ->setValue(array());
 
+    $fields[] = id(new PhabricatorHandlesEditField())
+      ->setKey('parents')
+      ->setUseEdgeTransactions(true)
+      ->setIsFormField(false)
+      ->setTransactionType(PhabricatorTransactions::TYPE_EDGE)
+      ->setMetadataValue(
+        'edge:type',
+        DifferentialRevisionDependsOnRevisionEdgeType::EDGECONST)
+      ->setDescription(pht('Parent revisions of this revision.'))
+      ->setConduitDescription(pht('Change associated parent revisions.'))
+      ->setConduitTypeDescription(pht('List of revisions.'))
+      ->setValue(array());
+
+    $fields[] = id(new PhabricatorHandlesEditField())
+      ->setKey('children')
+      ->setUseEdgeTransactions(true)
+      ->setIsFormField(false)
+      ->setTransactionType(PhabricatorTransactions::TYPE_EDGE)
+      ->setMetadataValue(
+        'edge:type',
+        DifferentialRevisionDependedOnByRevisionEdgeType::EDGECONST)
+      ->setDescription(pht('Child revisions of this revision.'))
+      ->setConduitDescription(pht('Change associated child revisions.'))
+      ->setConduitTypeDescription(pht('List of revisions.'))
+      ->setValue(array());
+
     $actions = DifferentialRevisionActionTransaction::loadAllActions();
     $actions = msortv($actions, 'getRevisionActionOrderVector');
 
diff --git a/src/applications/differential/engine/DifferentialDiffExtractionEngine.php b/src/applications/differential/engine/DifferentialDiffExtractionEngine.php
index d7d7c767e1..861d2ad220 100644
--- a/src/applications/differential/engine/DifferentialDiffExtractionEngine.php
+++ b/src/applications/differential/engine/DifferentialDiffExtractionEngine.php
@@ -177,14 +177,21 @@ final class DifferentialDiffExtractionEngine extends Phobject {
             'repository' => $repository,
           ));
 
-        $response = DiffusionQuery::callConduitWithDiffusionRequest(
-          $viewer,
-          $drequest,
-          'diffusion.filecontentquery',
-          array(
-            'commit' => $identifier,
-            'path' => $path,
-          ));
+        try {
+          $response = DiffusionQuery::callConduitWithDiffusionRequest(
+            $viewer,
+            $drequest,
+            'diffusion.filecontentquery',
+            array(
+              'commit' => $identifier,
+              'path' => $path,
+            ));
+        } catch (Exception $ex) {
+          // TODO: See PHI1044. This call may fail if the diff deleted the
+          // file. If the call fails, just detect a change for now. This should
+          // generally be made cleaner in the future.
+          return true;
+        }
 
         $new_file_phid = $response['filePHID'];
         if (!$new_file_phid) {
diff --git a/src/applications/diffusion/controller/DiffusionServeController.php b/src/applications/diffusion/controller/DiffusionServeController.php
index 5a5c446a29..cb4ad0ba95 100644
--- a/src/applications/diffusion/controller/DiffusionServeController.php
+++ b/src/applications/diffusion/controller/DiffusionServeController.php
@@ -528,7 +528,7 @@ final class DiffusionServeController extends DiffusionController {
         unset($query_data[$key]);
       }
     }
-    $query_string = http_build_query($query_data, '', '&');
+    $query_string = phutil_build_http_querystring($query_data);
 
     // We're about to wipe out PATH with the rest of the environment, so
     // resolve the binary first.
diff --git a/src/applications/diffusion/protocol/DiffusionRepositoryClusterEngine.php b/src/applications/diffusion/protocol/DiffusionRepositoryClusterEngine.php
index c72021f0c1..717e730ab1 100644
--- a/src/applications/diffusion/protocol/DiffusionRepositoryClusterEngine.php
+++ b/src/applications/diffusion/protocol/DiffusionRepositoryClusterEngine.php
@@ -188,7 +188,7 @@ final class DiffusionRepositoryClusterEngine extends Phobject {
     if ($this_version) {
       $this_version = (int)$this_version->getRepositoryVersion();
     } else {
-      $this_version = -1;
+      $this_version = null;
     }
 
     if ($versions) {
@@ -197,7 +197,7 @@ final class DiffusionRepositoryClusterEngine extends Phobject {
       // leader, we want to fetch from a leader and then update our version.
 
       $max_version = (int)max(mpull($versions, 'getRepositoryVersion'));
-      if ($max_version > $this_version) {
+      if (($this_version === null) || ($max_version > $this_version)) {
         if ($repository->isHosted()) {
           $fetchable = array();
           foreach ($versions as $version) {
@@ -206,6 +206,7 @@ final class DiffusionRepositoryClusterEngine extends Phobject {
             }
           }
 
+
           $this->synchronizeWorkingCopyFromDevices(
             $fetchable,
             $this_version,
@@ -445,10 +446,10 @@ final class DiffusionRepositoryClusterEngine extends Phobject {
     if ($this_version) {
       $this_version = (int)$this_version->getRepositoryVersion();
     } else {
-      $this_version = -1;
+      $this_version = null;
     }
 
-    if ($new_version > $this_version) {
+    if (($this_version === null) || ($new_version > $this_version)) {
       PhabricatorRepositoryWorkingCopyVersion::updateVersion(
         $repository_phid,
         $device_phid,
diff --git a/src/applications/diffusion/ssh/DiffusionSSHWorkflow.php b/src/applications/diffusion/ssh/DiffusionSSHWorkflow.php
index 02cacbfe94..b2d1d25f44 100644
--- a/src/applications/diffusion/ssh/DiffusionSSHWorkflow.php
+++ b/src/applications/diffusion/ssh/DiffusionSSHWorkflow.php
@@ -222,8 +222,10 @@ abstract class DiffusionSSHWorkflow extends PhabricatorSSHWorkflow {
         pht('No repository "%s" exists!', $identifier));
     }
 
+    $is_cluster = $this->getIsClusterRequest();
+
     $protocol = PhabricatorRepositoryURI::BUILTIN_PROTOCOL_SSH;
-    if (!$repository->canServeProtocol($protocol, false)) {
+    if (!$repository->canServeProtocol($protocol, false, $is_cluster)) {
       throw new Exception(
         pht(
           'This repository ("%s") is not available over SSH.',
diff --git a/src/applications/project/config/PhabricatorProjectConfigOptions.php b/src/applications/project/config/PhabricatorProjectConfigOptions.php
index c61faa64fb..2d87bf159f 100644
--- a/src/applications/project/config/PhabricatorProjectConfigOptions.php
+++ b/src/applications/project/config/PhabricatorProjectConfigOptions.php
@@ -83,6 +83,34 @@ EOTEXT
 
     $custom_field_type = 'custom:PhabricatorCustomFieldConfigOptionType';
 
+
+    $subtype_type = 'projects.subtypes';
+    $subtype_default_key = PhabricatorEditEngineSubtype::SUBTYPE_DEFAULT;
+    $subtype_example = array(
+      array(
+        'key' => $subtype_default_key,
+        'name' => pht('Project'),
+      ),
+      array(
+        'key' => 'team',
+        'name' => pht('Team'),
+      ),
+    );
+    $subtype_example = id(new PhutilJSON())->encodeAsList($subtype_example);
+
+    $subtype_default = array(
+      array(
+        'key' => $subtype_default_key,
+        'name' => pht('Project'),
+      ),
+    );
+
+    $subtype_description = $this->deformat(pht(<<<EOTEXT
+Allows you to define project subtypes. For a more detailed description of
+subtype configuration, see @{config:maniphest.subtypes}.
+EOTEXT
+      ));
+
     return array(
       $this->newOption('projects.custom-field-definitions', 'wild', array())
         ->setSummary(pht('Custom Projects fields.'))
@@ -102,6 +130,11 @@ EOTEXT
       $this->newOption('projects.colors', $colors_type, $default_colors)
         ->setSummary(pht('Adjust project colors.'))
         ->setDescription($colors_description),
+      $this->newOption('projects.subtypes', $subtype_type, $subtype_default)
+        ->setSummary(pht('Define project subtypes.'))
+        ->setDescription($subtype_description)
+        ->addExample($subtype_example, pht('Simple Subtypes')),
+
     );
   }
 
diff --git a/src/applications/project/config/PhabricatorProjectSubtypesConfigType.php b/src/applications/project/config/PhabricatorProjectSubtypesConfigType.php
new file mode 100644
index 0000000000..7603ad7683
--- /dev/null
+++ b/src/applications/project/config/PhabricatorProjectSubtypesConfigType.php
@@ -0,0 +1,14 @@
+<?php
+
+final class PhabricatorProjectSubtypesConfigType
+  extends PhabricatorJSONConfigType {
+
+  const TYPEKEY = 'projects.subtypes';
+
+  public function validateStoredValue(
+    PhabricatorConfigOption $option,
+    $value) {
+    PhabricatorEditEngineSubtype::validateConfiguration($value);
+  }
+
+}
diff --git a/src/applications/project/controller/PhabricatorProjectProfileController.php b/src/applications/project/controller/PhabricatorProjectProfileController.php
index 1f59398930..6e1e7677e6 100644
--- a/src/applications/project/controller/PhabricatorProjectProfileController.php
+++ b/src/applications/project/controller/PhabricatorProjectProfileController.php
@@ -51,6 +51,12 @@ final class PhabricatorProjectProfileController
     $watch_action = $this->renderWatchAction($project);
     $header->addActionLink($watch_action);
 
+    $subtype = $project->newSubtypeObject();
+    if ($subtype && $subtype->hasTagView()) {
+      $subtype_tag = $subtype->newTagView();
+      $header->addTag($subtype_tag);
+    }
+
     $milestone_list = $this->buildMilestoneList($project);
     $subproject_list = $this->buildSubprojectList($project);
 
diff --git a/src/applications/project/editor/PhabricatorProjectTransactionEditor.php b/src/applications/project/editor/PhabricatorProjectTransactionEditor.php
index ee2c087085..b714f66830 100644
--- a/src/applications/project/editor/PhabricatorProjectTransactionEditor.php
+++ b/src/applications/project/editor/PhabricatorProjectTransactionEditor.php
@@ -249,6 +249,17 @@ final class PhabricatorProjectTransactionEditor
         ->rematerialize($new_parent);
     }
 
+    // See PHI1046. Milestones are always in the Space of their parent project.
+    // Synchronize the database values to match the application values.
+    $conn = $object->establishConnection('w');
+    queryfx(
+      $conn,
+      'UPDATE %R SET spacePHID = %ns
+        WHERE parentProjectPHID = %s AND milestoneNumber IS NOT NULL',
+      $object,
+      $object->getSpacePHID(),
+      $object->getPHID());
+
     return parent::applyFinalEffects($object, $xactions);
   }
 
diff --git a/src/applications/project/query/PhabricatorProjectQuery.php b/src/applications/project/query/PhabricatorProjectQuery.php
index 6f81bc5e68..f6087f7d2a 100644
--- a/src/applications/project/query/PhabricatorProjectQuery.php
+++ b/src/applications/project/query/PhabricatorProjectQuery.php
@@ -24,6 +24,7 @@ final class PhabricatorProjectQuery
   private $maxDepth;
   private $minMilestoneNumber;
   private $maxMilestoneNumber;
+  private $subtypes;
 
   private $status       = 'status-any';
   const STATUS_ANY      = 'status-any';
@@ -131,6 +132,11 @@ final class PhabricatorProjectQuery
     return $this;
   }
 
+  public function withSubtypes(array $subtypes) {
+    $this->subtypes = $subtypes;
+    return $this;
+  }
+
   public function needMembers($need_members) {
     $this->needMembers = $need_members;
     return $this;
@@ -618,6 +624,13 @@ final class PhabricatorProjectQuery
         $this->maxMilestoneNumber);
     }
 
+    if ($this->subtypes !== null) {
+      $where[] = qsprintf(
+        $conn,
+        'subtype IN (%Ls)',
+        $this->subtypes);
+    }
+
     return $where;
   }
 
diff --git a/src/applications/project/query/PhabricatorProjectSearchEngine.php b/src/applications/project/query/PhabricatorProjectSearchEngine.php
index 02e795395a..88a35676cc 100644
--- a/src/applications/project/query/PhabricatorProjectSearchEngine.php
+++ b/src/applications/project/query/PhabricatorProjectSearchEngine.php
@@ -19,6 +19,9 @@ final class PhabricatorProjectSearchEngine
   }
 
   protected function buildCustomSearchFields() {
+    $subtype_map = id(new PhabricatorProject())->newEditEngineSubtypeMap();
+    $hide_subtypes = ($subtype_map->getCount() == 1);
+
     return array(
       id(new PhabricatorSearchTextField())
         ->setLabel(pht('Name'))
@@ -62,6 +65,14 @@ final class PhabricatorProjectSearchEngine
           pht(
             'Pass true to find only milestones, or false to omit '.
             'milestones.')),
+      id(new PhabricatorSearchDatasourceField())
+        ->setLabel(pht('Subtypes'))
+        ->setKey('subtypes')
+        ->setAliases(array('subtype'))
+        ->setDescription(
+          pht('Search for projects with given subtypes.'))
+        ->setDatasource(new PhabricatorProjectSubtypeDatasource())
+        ->setIsHidden($hide_subtypes),
       id(new PhabricatorSearchCheckboxesField())
         ->setLabel(pht('Icons'))
         ->setKey('icons')
@@ -134,6 +145,10 @@ final class PhabricatorProjectSearchEngine
       $query->withAncestorProjectPHIDs($map['ancestorPHIDs']);
     }
 
+    if ($map['subtypes']) {
+      $query->withSubtypes($map['subtypes']);
+    }
+
     return $query;
   }
 
diff --git a/src/applications/project/storage/PhabricatorProject.php b/src/applications/project/storage/PhabricatorProject.php
index 4dae13f3c6..5182a941bf 100644
--- a/src/applications/project/storage/PhabricatorProject.php
+++ b/src/applications/project/storage/PhabricatorProject.php
@@ -12,7 +12,8 @@ final class PhabricatorProject extends PhabricatorProjectDAO
     PhabricatorFerretInterface,
     PhabricatorConduitResultInterface,
     PhabricatorColumnProxyInterface,
-    PhabricatorSpacesInterface {
+    PhabricatorSpacesInterface,
+    PhabricatorEditEngineSubtypeInterface {
 
   protected $name;
   protected $status = PhabricatorProjectStatus::STATUS_ACTIVE;
@@ -40,6 +41,7 @@ final class PhabricatorProject extends PhabricatorProjectDAO
 
   protected $properties = array();
   protected $spacePHID;
+  protected $subtype;
 
   private $memberPHIDs = self::ATTACHABLE;
   private $watcherPHIDs = self::ATTACHABLE;
@@ -102,6 +104,7 @@ final class PhabricatorProject extends PhabricatorProjectDAO
       ->setHasWorkboard(0)
       ->setHasMilestones(0)
       ->setHasSubprojects(0)
+      ->setSubtype(PhabricatorEditEngineSubtype::SUBTYPE_DEFAULT)
       ->attachParentProject(null);
   }
 
@@ -237,6 +240,7 @@ final class PhabricatorProject extends PhabricatorProjectDAO
         'projectPath' => 'hashpath64',
         'projectDepth' => 'uint32',
         'projectPathKey' => 'bytes4',
+        'subtype' => 'text64',
       ),
       self::CONFIG_KEY_SCHEMA => array(
         'key_icon' => array(
@@ -765,6 +769,10 @@ final class PhabricatorProject extends PhabricatorProjectDAO
         ->setKey('slug')
         ->setType('string')
         ->setDescription(pht('Primary slug/hashtag.')),
+      id(new PhabricatorConduitSearchFieldSpecification())
+        ->setKey('subtype')
+        ->setType('string')
+        ->setDescription(pht('Subtype of the project.')),
       id(new PhabricatorConduitSearchFieldSpecification())
         ->setKey('milestone')
         ->setType('int?')
@@ -814,6 +822,7 @@ final class PhabricatorProject extends PhabricatorProjectDAO
     return array(
       'name' => $this->getName(),
       'slug' => $this->getPrimarySlug(),
+      'subtype' => $this->getSubtype(),
       'milestone' => $milestone,
       'depth' => (int)$this->getProjectDepth(),
       'parent' => $parent_ref,
@@ -873,4 +882,26 @@ final class PhabricatorProject extends PhabricatorProjectDAO
   }
 
 
+/* -(  PhabricatorEditEngineSubtypeInterface  )------------------------------ */
+
+
+  public function getEditEngineSubtype() {
+    return $this->getSubtype();
+  }
+
+  public function setEditEngineSubtype($value) {
+    return $this->setSubtype($value);
+  }
+
+  public function newEditEngineSubtypeMap() {
+    $config = PhabricatorEnv::getEnvConfig('projects.subtypes');
+    return PhabricatorEditEngineSubtype::newSubtypeMap($config);
+  }
+
+  public function newSubtypeObject() {
+    $subtype_key = $this->getEditEngineSubtype();
+    $subtype_map = $this->newEditEngineSubtypeMap();
+    return $subtype_map->getSubtype($subtype_key);
+  }
+
 }
diff --git a/src/applications/project/typeahead/PhabricatorProjectSubtypeDatasource.php b/src/applications/project/typeahead/PhabricatorProjectSubtypeDatasource.php
new file mode 100644
index 0000000000..68de11e630
--- /dev/null
+++ b/src/applications/project/typeahead/PhabricatorProjectSubtypeDatasource.php
@@ -0,0 +1,45 @@
+<?php
+
+final class PhabricatorProjectSubtypeDatasource
+  extends PhabricatorTypeaheadDatasource {
+
+  public function getBrowseTitle() {
+    return pht('Browse Subtypes');
+  }
+
+  public function getPlaceholderText() {
+    return pht('Type a project subtype name...');
+  }
+
+  public function getDatasourceApplicationClass() {
+    return 'PhabricatorProjectApplication';
+  }
+
+  public function loadResults() {
+    $results = $this->buildResults();
+    return $this->filterResultsAgainstTokens($results);
+  }
+
+  protected function renderSpecialTokens(array $values) {
+    return $this->renderTokensFromResults($this->buildResults(), $values);
+  }
+
+  private function buildResults() {
+    $results = array();
+
+    $subtype_map = id(new PhabricatorProject())->newEditEngineSubtypeMap();
+    foreach ($subtype_map->getSubtypes() as $key => $subtype) {
+
+      $result = id(new PhabricatorTypeaheadResult())
+        ->setIcon($subtype->getIcon())
+        ->setColor($subtype->getColor())
+        ->setPHID($key)
+        ->setName($subtype->getName());
+
+      $results[$key] = $result;
+    }
+
+    return $results;
+  }
+
+}
diff --git a/src/applications/project/view/PhabricatorProjectListView.php b/src/applications/project/view/PhabricatorProjectListView.php
index 645440d831..d8fb011c2e 100644
--- a/src/applications/project/view/PhabricatorProjectListView.php
+++ b/src/applications/project/view/PhabricatorProjectListView.php
@@ -87,6 +87,13 @@ final class PhabricatorProjectListView extends AphrontView {
         }
       }
 
+      $subtype = $project->newSubtypeObject();
+      if ($subtype && $subtype->hasTagView()) {
+        $subtype_tag = $subtype->newTagView()
+          ->setSlimShady(true);
+        $item->addAttribute($subtype_tag);
+      }
+
       $list->addItem($item);
     }
 
diff --git a/src/applications/repository/daemon/PhabricatorRepositoryPullLocalDaemon.php b/src/applications/repository/daemon/PhabricatorRepositoryPullLocalDaemon.php
index 332d67f7af..125ee833f8 100644
--- a/src/applications/repository/daemon/PhabricatorRepositoryPullLocalDaemon.php
+++ b/src/applications/repository/daemon/PhabricatorRepositoryPullLocalDaemon.php
@@ -73,6 +73,9 @@ final class PhabricatorRepositoryPullLocalDaemon
     $futures = array();
     $queue = array();
 
+    $sync_wait = phutil_units('2 minutes in seconds');
+    $last_sync = array();
+
     while (!$this->shouldExit()) {
       PhabricatorCaches::destroyRequestCache();
       $device = AlmanacKeys::getLiveDevice();
@@ -96,6 +99,37 @@ final class PhabricatorRepositoryPullLocalDaemon
         $retry_after[$message->getRepositoryID()] = time();
       }
 
+      if ($device) {
+        $unsynchronized = $this->loadUnsynchronizedRepositories($device);
+        $now = PhabricatorTime::getNow();
+        foreach ($unsynchronized as $repository) {
+          $id = $repository->getID();
+
+          $this->log(
+            pht(
+              'Cluster repository ("%s") is out of sync on this node ("%s").',
+              $repository->getDisplayName(),
+              $device->getName()));
+
+          // Don't let out-of-sync conditions trigger updates too frequently,
+          // since we don't want to get trapped in a death spiral if sync is
+          // failing.
+          $sync_at = idx($last_sync, $id, 0);
+          $wait_duration = ($now - $sync_at);
+          if ($wait_duration < $sync_wait) {
+            $this->log(
+              pht(
+                'Skipping forced out-of-sync update because the last update '.
+                'was too recent (%s seconds ago).',
+                $wait_duration));
+            continue;
+          }
+
+          $last_sync[$id] = $now;
+          $retry_after[$id] = $now;
+        }
+      }
+
       // If any repositories were deleted, remove them from the retry timer map
       // so we don't end up with a retry timer that never gets updated and
       // causes us to sleep for the minimum amount of time.
@@ -521,4 +555,41 @@ final class PhabricatorRepositoryPullLocalDaemon
     return false;
   }
 
+  private function loadUnsynchronizedRepositories(AlmanacDevice $device) {
+    $viewer = $this->getViewer();
+    $table = new PhabricatorRepositoryWorkingCopyVersion();
+    $conn = $table->establishConnection('r');
+
+    $our_versions = queryfx_all(
+      $conn,
+      'SELECT repositoryPHID, repositoryVersion FROM %R WHERE devicePHID = %s',
+      $table,
+      $device->getPHID());
+    $our_versions = ipull($our_versions, 'repositoryVersion', 'repositoryPHID');
+
+    $max_versions = queryfx_all(
+      $conn,
+      'SELECT repositoryPHID, MAX(repositoryVersion) maxVersion FROM %R
+        GROUP BY repositoryPHID',
+      $table);
+    $max_versions = ipull($max_versions, 'maxVersion', 'repositoryPHID');
+
+    $unsynchronized_phids = array();
+    foreach ($max_versions as $repository_phid => $max_version) {
+      $our_version = idx($our_versions, $repository_phid);
+      if (($our_version === null) || ($our_version < $max_version)) {
+        $unsynchronized_phids[] = $repository_phid;
+      }
+    }
+
+    if (!$unsynchronized_phids) {
+      return array();
+    }
+
+    return id(new PhabricatorRepositoryQuery())
+      ->setViewer($viewer)
+      ->withPHIDs($unsynchronized_phids)
+      ->execute();
+  }
+
 }
diff --git a/src/applications/repository/management/PhabricatorRepositoryManagementWorkflow.php b/src/applications/repository/management/PhabricatorRepositoryManagementWorkflow.php
index 654a974e6c..6d48d7c5d1 100644
--- a/src/applications/repository/management/PhabricatorRepositoryManagementWorkflow.php
+++ b/src/applications/repository/management/PhabricatorRepositoryManagementWorkflow.php
@@ -7,7 +7,7 @@ abstract class PhabricatorRepositoryManagementWorkflow
     $identifiers = $args->getArg($param);
 
     if (!$identifiers) {
-      return null;
+      return array();
     }
 
     $query = id(new PhabricatorRepositoryQuery())
diff --git a/src/applications/repository/storage/PhabricatorRepository.php b/src/applications/repository/storage/PhabricatorRepository.php
index ed90f47f13..e66fb78afa 100644
--- a/src/applications/repository/storage/PhabricatorRepository.php
+++ b/src/applications/repository/storage/PhabricatorRepository.php
@@ -1506,9 +1506,18 @@ final class PhabricatorRepository extends PhabricatorRepositoryDAO
     return $this->setDetail('hosting-enabled', $enabled);
   }
 
-  public function canServeProtocol($protocol, $write) {
-    if (!$this->isTracked()) {
-      return false;
+  public function canServeProtocol(
+    $protocol,
+    $write,
+    $is_intracluster = false) {
+
+    // See T13192. If a repository is inactive, don't serve it to users. We
+    // still synchronize it within the cluster and serve it to other repository
+    // nodes.
+    if (!$is_intracluster) {
+      if (!$this->isTracked()) {
+        return false;
+      }
     }
 
     $clone_uris = $this->getCloneURIs();
diff --git a/src/applications/settings/panel/PhabricatorMultiFactorSettingsPanel.php b/src/applications/settings/panel/PhabricatorMultiFactorSettingsPanel.php
index 4da09dd324..6809b51334 100644
--- a/src/applications/settings/panel/PhabricatorMultiFactorSettingsPanel.php
+++ b/src/applications/settings/panel/PhabricatorMultiFactorSettingsPanel.php
@@ -256,13 +256,16 @@ final class PhabricatorMultiFactorSettingsPanel
     // sometimes requires us to push a challenge to them as a side effect (for
     // example, with SMS).
     if (!$request->isFormPost() || !$request->getBool('mfa.start')) {
-      $description = $selected_provider->getEnrollDescription($viewer);
+      $enroll = $selected_provider->getEnrollMessage();
+      if (!strlen($enroll)) {
+        $enroll = $selected_provider->getEnrollDescription($viewer);
+      }
 
       return $this->newDialog()
         ->addHiddenInput('providerPHID', $selected_provider->getPHID())
         ->addHiddenInput('mfa.start', 1)
         ->setTitle(pht('Add Authentication Factor'))
-        ->appendChild(new PHUIRemarkupView($viewer, $description))
+        ->appendChild(new PHUIRemarkupView($viewer, $enroll))
         ->addCancelButton($cancel_uri)
         ->addSubmitButton($selected_provider->getEnrollButtonText($viewer));
     }
diff --git a/src/applications/transactions/conduit/TransactionSearchConduitAPIMethod.php b/src/applications/transactions/conduit/TransactionSearchConduitAPIMethod.php
index 0394432ff3..0edc0b3f5a 100644
--- a/src/applications/transactions/conduit/TransactionSearchConduitAPIMethod.php
+++ b/src/applications/transactions/conduit/TransactionSearchConduitAPIMethod.php
@@ -68,6 +68,7 @@ final class TransactionSearchConduitAPIMethod
       $object);
 
     $xaction_query
+      ->needHandles(false)
       ->withObjectPHIDs(array($object->getPHID()))
       ->setViewer($viewer);
 
diff --git a/src/applications/transactions/editengine/PhabricatorEditEngine.php b/src/applications/transactions/editengine/PhabricatorEditEngine.php
index b3106d27b2..feb783e724 100644
--- a/src/applications/transactions/editengine/PhabricatorEditEngine.php
+++ b/src/applications/transactions/editengine/PhabricatorEditEngine.php
@@ -1279,14 +1279,41 @@ abstract class PhabricatorEditEngine
 
     $fields = $this->willBuildEditForm($object, $fields);
 
+    $request_path = $request->getRequestURI()
+      ->setQueryParams(array());
+
     $form = id(new AphrontFormView())
       ->setUser($viewer)
+      ->setAction($request_path)
       ->addHiddenInput('editEngine', 'true');
 
     foreach ($this->contextParameters as $param) {
       $form->addHiddenInput($param, $request->getStr($param));
     }
 
+    $requires_mfa = false;
+    if ($object instanceof PhabricatorEditEngineMFAInterface) {
+      $mfa_engine = PhabricatorEditEngineMFAEngine::newEngineForObject($object)
+        ->setViewer($viewer);
+      $requires_mfa = $mfa_engine->shouldRequireMFA();
+    }
+
+    if ($requires_mfa) {
+      $message = pht(
+        'You will be required to provide multi-factor credentials to make '.
+        'changes.');
+      $form->appendChild(
+        id(new PHUIInfoView())
+          ->setSeverity(PHUIInfoView::SEVERITY_MFA)
+          ->setErrors(array($message)));
+
+      // TODO: This should also set workflow on the form, so the user doesn't
+      // lose any form data if they "Cancel". However, Maniphest currently
+      // overrides "newEditResponse()" if the request is Ajax and returns a
+      // bag of view data. This can reasonably be cleaned up when workboards
+      // get their next iteration.
+    }
+
     foreach ($fields as $field) {
       if (!$field->getIsFormField()) {
         continue;
@@ -1565,11 +1592,19 @@ abstract class PhabricatorEditEngine
 
     $comment_uri = $this->getEditURI($object, 'comment/');
 
+    $requires_mfa = false;
+    if ($object instanceof PhabricatorEditEngineMFAInterface) {
+      $mfa_engine = PhabricatorEditEngineMFAEngine::newEngineForObject($object)
+        ->setViewer($viewer);
+      $requires_mfa = $mfa_engine->shouldRequireMFA();
+    }
+
     $view = id(new PhabricatorApplicationTransactionCommentView())
       ->setUser($viewer)
       ->setObjectPHID($object_phid)
       ->setHeaderText($header_text)
       ->setAction($comment_uri)
+      ->setRequiresMFA($requires_mfa)
       ->setSubmitButtonName($button_text);
 
     $draft = PhabricatorVersionedDraft::loadDraft(
diff --git a/src/applications/transactions/editor/PhabricatorApplicationTransactionEditor.php b/src/applications/transactions/editor/PhabricatorApplicationTransactionEditor.php
index c6458b0631..91825eb73d 100644
--- a/src/applications/transactions/editor/PhabricatorApplicationTransactionEditor.php
+++ b/src/applications/transactions/editor/PhabricatorApplicationTransactionEditor.php
@@ -88,6 +88,7 @@ abstract class PhabricatorApplicationTransactionEditor
   private $hasRequiredMFA = false;
   private $request;
   private $cancelURI;
+  private $extensions;
 
   const STORAGE_ENCODING_BINARY = 'binary';
 
@@ -1013,6 +1014,7 @@ abstract class PhabricatorApplicationTransactionEditor
       }
 
       $errors[] = $this->validateAllTransactions($object, $xactions);
+      $errors[] = $this->validateTransactionsWithExtensions($object, $xactions);
       $errors = array_mergev($errors);
 
       $continue_on_missing = $this->getContinueOnMissingFields();
@@ -2667,9 +2669,15 @@ abstract class PhabricatorApplicationTransactionEditor
     $transaction_type) {
     $errors = array();
 
-    $factors = id(new PhabricatorAuthFactorConfig())->loadAllWhere(
-      'userPHID = %s',
-      $this->getActingAsPHID());
+    $factors = id(new PhabricatorAuthFactorConfigQuery())
+      ->setViewer($this->getActor())
+      ->withUserPHIDs(array($this->getActingAsPHID()))
+      ->withFactorProviderStatuses(
+        array(
+          PhabricatorAuthFactorProviderStatus::STATUS_ACTIVE,
+          PhabricatorAuthFactorProviderStatus::STATUS_DEPRECATED,
+        ))
+      ->execute();
 
     foreach ($xactions as $xaction) {
       if (!$factors) {
@@ -3286,7 +3294,7 @@ abstract class PhabricatorApplicationTransactionEditor
       // move the other transactions down so they provide context above the
       // actual comment.
 
-      $comment = $xaction->getBodyForMail();
+      $comment = $this->getBodyForTextMail($xaction);
       if ($comment !== null) {
         $is_comment = true;
         $comments[] = array(
@@ -3299,12 +3307,12 @@ abstract class PhabricatorApplicationTransactionEditor
       }
 
       if (!$is_comment || !$seen_comment) {
-        $header = $xaction->getTitleForTextMail();
+        $header = $this->getTitleForTextMail($xaction);
         if ($header !== null) {
           $headers[] = $header;
         }
 
-        $header_html = $xaction->getTitleForHTMLMail();
+        $header_html = $this->getTitleForHTMLMail($xaction);
         if ($header_html !== null) {
           $headers_html[] = $header_html;
         }
@@ -3384,12 +3392,12 @@ abstract class PhabricatorApplicationTransactionEditor
       // If this is not the first comment in the mail, add the header showing
       // who wrote the comment immediately above the comment.
       if (!$is_initial) {
-        $header = $xaction->getTitleForTextMail();
+        $header = $this->getTitleForTextMail($xaction);
         if ($header !== null) {
           $body->addRawPlaintextSection($header);
         }
 
-        $header_html = $xaction->getTitleForHTMLMail();
+        $header_html = $this->getTitleForHTMLMail($xaction);
         if ($header_html !== null) {
           $body->addRawHTMLSection($header_html);
         }
@@ -4848,6 +4856,13 @@ abstract class PhabricatorApplicationTransactionEditor
   }
 
   private function requireMFA(PhabricatorLiskDAO $object, array $xactions) {
+    $actor = $this->getActor();
+
+    // Let omnipotent editors skip MFA. This is mostly aimed at scripts.
+    if ($actor->isOmnipotent()) {
+      return;
+    }
+
     $editor_class = get_class($this);
 
     $object_phid = $object->getPHID();
@@ -4862,8 +4877,6 @@ abstract class PhabricatorApplicationTransactionEditor
         $editor_class);
     }
 
-    $actor = $this->getActor();
-
     $request = $this->getRequest();
     if ($request === null) {
       $source_type = $this->getContentSource()->getSourceTypeConstant();
@@ -4975,4 +4988,112 @@ abstract class PhabricatorApplicationTransactionEditor
     return $xactions;
   }
 
+  private function getTitleForTextMail(
+    PhabricatorApplicationTransaction $xaction) {
+    $type = $xaction->getTransactionType();
+
+    $xtype = $this->getModularTransactionType($type);
+    if ($xtype) {
+      $xtype = clone $xtype;
+      $xtype->setStorage($xaction);
+      $comment = $xtype->getTitleForTextMail();
+      if ($comment !== false) {
+        return $comment;
+      }
+    }
+
+    return $xaction->getTitleForTextMail();
+  }
+
+  private function getTitleForHTMLMail(
+    PhabricatorApplicationTransaction $xaction) {
+    $type = $xaction->getTransactionType();
+
+    $xtype = $this->getModularTransactionType($type);
+    if ($xtype) {
+      $xtype = clone $xtype;
+      $xtype->setStorage($xaction);
+      $comment = $xtype->getTitleForHTMLMail();
+      if ($comment !== false) {
+        return $comment;
+      }
+    }
+
+    return $xaction->getTitleForHTMLMail();
+  }
+
+
+  private function getBodyForTextMail(
+    PhabricatorApplicationTransaction $xaction) {
+    $type = $xaction->getTransactionType();
+
+    $xtype = $this->getModularTransactionType($type);
+    if ($xtype) {
+      $xtype = clone $xtype;
+      $xtype->setStorage($xaction);
+      $comment = $xtype->getBodyForTextMail();
+      if ($comment !== false) {
+        return $comment;
+      }
+    }
+
+    return $xaction->getBodyForMail();
+  }
+
+
+/* -(  Extensions  )--------------------------------------------------------- */
+
+
+  private function validateTransactionsWithExtensions(
+    PhabricatorLiskDAO $object,
+    array $xactions) {
+    $errors = array();
+
+    $extensions = $this->getEditorExtensions();
+    foreach ($extensions as $extension) {
+      $extension_errors = $extension
+        ->setObject($object)
+        ->validateTransactions($object, $xactions);
+
+      assert_instances_of(
+        $extension_errors,
+        'PhabricatorApplicationTransactionValidationError');
+
+      $errors[] = $extension_errors;
+    }
+
+    return array_mergev($errors);
+  }
+
+  private function getEditorExtensions() {
+    if ($this->extensions === null) {
+      $this->extensions = $this->newEditorExtensions();
+    }
+    return $this->extensions;
+  }
+
+  private function newEditorExtensions() {
+    $extensions = PhabricatorEditorExtension::getAllExtensions();
+
+    $actor = $this->getActor();
+    $object = $this->object;
+    foreach ($extensions as $key => $extension) {
+
+      $extension = id(clone $extension)
+        ->setViewer($actor)
+        ->setEditor($this)
+        ->setObject($object);
+
+      if (!$extension->supportsObject($this, $object)) {
+        unset($extensions[$key]);
+        continue;
+      }
+
+      $extensions[$key] = $extension;
+    }
+
+    return $extensions;
+  }
+
+
 }
diff --git a/src/applications/transactions/engineextension/PhabricatorEditorExtension.php b/src/applications/transactions/engineextension/PhabricatorEditorExtension.php
new file mode 100644
index 0000000000..6ffac522c2
--- /dev/null
+++ b/src/applications/transactions/engineextension/PhabricatorEditorExtension.php
@@ -0,0 +1,83 @@
+<?php
+
+abstract class PhabricatorEditorExtension
+  extends Phobject {
+
+  private $viewer;
+  private $editor;
+  private $object;
+
+  final public function getExtensionKey() {
+    return $this->getPhobjectClassConstant('EXTENSIONKEY');
+  }
+
+  final public function setEditor(
+    PhabricatorApplicationTransactionEditor $editor) {
+    $this->editor = $editor;
+    return $this;
+  }
+
+  final public function getEditor() {
+    return $this->editor;
+  }
+
+  final public function setViewer(PhabricatorUser $viewer) {
+    $this->viewer = $viewer;
+    return $this;
+  }
+
+  final public function getViewer() {
+    return $this->viewer;
+  }
+
+  final public function setObject(
+    PhabricatorApplicationTransactionInterface $object) {
+    $this->object = $object;
+    return $this;
+  }
+
+  final public static function getAllExtensions() {
+    return id(new PhutilClassMapQuery())
+      ->setAncestorClass(__CLASS__)
+      ->setUniqueMethod('getExtensionKey')
+      ->execute();
+  }
+
+  abstract public function getExtensionName();
+
+  public function supportsObject(
+    PhabricatorApplicationTransactionEditor $editor,
+    PhabricatorApplicationTransactionInterface $object) {
+    return true;
+  }
+
+  public function validateTransactions($object, array $xactions) {
+    return array();
+  }
+
+  final protected function newTransactionError(
+    PhabricatorApplicationTransaction $xaction,
+    $title,
+    $message) {
+    return new PhabricatorApplicationTransactionValidationError(
+      $xaction->getTransactionType(),
+      $title,
+      $message,
+      $xaction);
+  }
+
+  final protected function newRequiredTransasctionError(
+    PhabricatorApplicationTransaction $xaction,
+    $message) {
+    return $this->newError($xaction, pht('Required'), $message)
+      ->setIsMissingFieldError(true);
+  }
+
+  final protected function newInvalidTransactionError(
+    PhabricatorApplicationTransaction $xaction,
+    $message) {
+    return $this->newTransactionError($xaction, pht('Invalid'), $message);
+  }
+
+
+}
diff --git a/src/applications/transactions/engineextension/PhabricatorEditorExtensionModule.php b/src/applications/transactions/engineextension/PhabricatorEditorExtensionModule.php
new file mode 100644
index 0000000000..e34a0bb3a7
--- /dev/null
+++ b/src/applications/transactions/engineextension/PhabricatorEditorExtensionModule.php
@@ -0,0 +1,40 @@
+<?php
+
+final class PhabricatorEditorExtensionModule
+  extends PhabricatorConfigModule {
+
+  public function getModuleKey() {
+    return 'editor';
+  }
+
+  public function getModuleName() {
+    return pht('Engine: Editor');
+  }
+
+  public function renderModuleStatus(AphrontRequest $request) {
+    $viewer = $request->getViewer();
+
+    $extensions = PhabricatorEditorExtension::getAllExtensions();
+
+    $rows = array();
+    foreach ($extensions as $extension) {
+      $rows[] = array(
+        get_class($extension),
+        $extension->getExtensionName(),
+      );
+    }
+
+    return id(new AphrontTableView($rows))
+      ->setHeaders(
+        array(
+          pht('Class'),
+          pht('Name'),
+        ))
+      ->setColumnClasses(
+        array(
+          null,
+          'wide pri',
+        ));
+  }
+
+}
diff --git a/src/applications/transactions/storage/PhabricatorApplicationTransaction.php b/src/applications/transactions/storage/PhabricatorApplicationTransaction.php
index efbbdb4a09..6d047fc823 100644
--- a/src/applications/transactions/storage/PhabricatorApplicationTransaction.php
+++ b/src/applications/transactions/storage/PhabricatorApplicationTransaction.php
@@ -740,8 +740,9 @@ abstract class PhabricatorApplicationTransaction
 
     switch ($this->getTransactionType()) {
       case PhabricatorTransactions::TYPE_TOKEN:
+      case PhabricatorTransactions::TYPE_MFA:
         return true;
-     case PhabricatorTransactions::TYPE_EDGE:
+      case PhabricatorTransactions::TYPE_EDGE:
         $edge_type = $this->getMetadataValue('edge:type');
         switch ($edge_type) {
           case PhabricatorObjectMentionsObjectEdgeType::EDGECONST:
diff --git a/src/applications/transactions/storage/PhabricatorModularTransactionType.php b/src/applications/transactions/storage/PhabricatorModularTransactionType.php
index abe7a31025..2d0cb8e7c1 100644
--- a/src/applications/transactions/storage/PhabricatorModularTransactionType.php
+++ b/src/applications/transactions/storage/PhabricatorModularTransactionType.php
@@ -431,4 +431,68 @@ abstract class PhabricatorModularTransactionType
     return false;
   }
 
+  // NOTE: See T12921. These APIs are somewhat aspirational. For now, all of
+  // these use "TARGET_TEXT" (even the HTML methods!) and the body methods
+  // actually return Remarkup, not text or HTML.
+
+  final public function getTitleForTextMail() {
+    return $this->getTitleForMailWithRenderingTarget(
+      PhabricatorApplicationTransaction::TARGET_TEXT);
+  }
+
+  final public function getTitleForHTMLMail() {
+    return $this->getTitleForMailWithRenderingTarget(
+      PhabricatorApplicationTransaction::TARGET_TEXT);
+  }
+
+  final public function getBodyForTextMail() {
+    return $this->getBodyForMailWithRenderingTarget(
+      PhabricatorApplicationTransaction::TARGET_TEXT);
+  }
+
+  final public function getBodyForHTMLMail() {
+    return $this->getBodyForMailWithRenderingTarget(
+      PhabricatorApplicationTransaction::TARGET_TEXT);
+  }
+
+  private function getTitleForMailWithRenderingTarget($target) {
+    $storage = $this->getStorage();
+
+    $old_target = $storage->getRenderingTarget();
+    try {
+      $storage->setRenderingTarget($target);
+      $result = $this->getTitleForMail();
+    } catch (Exception $ex) {
+      $storage->setRenderingTarget($old_target);
+      throw $ex;
+    }
+    $storage->setRenderingTarget($old_target);
+
+    return $result;
+  }
+
+  private function getBodyForMailWithRenderingTarget($target) {
+    $storage = $this->getStorage();
+
+    $old_target = $storage->getRenderingTarget();
+    try {
+      $storage->setRenderingTarget($target);
+      $result = $this->getBodyForMail();
+    } catch (Exception $ex) {
+      $storage->setRenderingTarget($old_target);
+      throw $ex;
+    }
+    $storage->setRenderingTarget($old_target);
+
+    return $result;
+  }
+
+  protected function getTitleForMail() {
+    return false;
+  }
+
+  protected function getBodyForMail() {
+    return false;
+  }
+
 }
diff --git a/src/applications/transactions/view/PhabricatorApplicationTransactionCommentView.php b/src/applications/transactions/view/PhabricatorApplicationTransactionCommentView.php
index d830309119..f6a27d4bcd 100644
--- a/src/applications/transactions/view/PhabricatorApplicationTransactionCommentView.php
+++ b/src/applications/transactions/view/PhabricatorApplicationTransactionCommentView.php
@@ -1,9 +1,7 @@
 <?php
 
-/**
- * @concrete-extensible
- */
-class PhabricatorApplicationTransactionCommentView extends AphrontView {
+final class PhabricatorApplicationTransactionCommentView
+  extends AphrontView {
 
   private $submitButtonName;
   private $action;
@@ -24,6 +22,7 @@ class PhabricatorApplicationTransactionCommentView extends AphrontView {
   private $infoView;
   private $editEngineLock;
   private $noBorder;
+  private $requiresMFA;
 
   private $currentVersion;
   private $versionedDraft;
@@ -160,6 +159,15 @@ class PhabricatorApplicationTransactionCommentView extends AphrontView {
     return $this->editEngineLock;
   }
 
+  public function setRequiresMFA($requires_mfa) {
+    $this->requiresMFA = $requires_mfa;
+    return $this;
+  }
+
+  public function getRequiresMFA() {
+    return $this->requiresMFA;
+  }
+
   public function setTransactionTimeline(
     PhabricatorApplicationTransactionView $timeline) {
 
@@ -187,8 +195,8 @@ class PhabricatorApplicationTransactionCommentView extends AphrontView {
           ));
     }
 
-    $user = $this->getUser();
-    if (!$user->isLoggedIn()) {
+    $viewer = $this->getViewer();
+    if (!$viewer->isLoggedIn()) {
       $uri = id(new PhutilURI('/login/'))
         ->setQueryParam('next', (string)$this->getRequestURI());
       return id(new PHUIObjectBoxView())
@@ -203,6 +211,25 @@ class PhabricatorApplicationTransactionCommentView extends AphrontView {
             pht('Log In to Comment')));
     }
 
+    if ($this->getRequiresMFA()) {
+      if (!$viewer->getIsEnrolledInMultiFactor()) {
+        $viewer->updateMultiFactorEnrollment();
+        if (!$viewer->getIsEnrolledInMultiFactor()) {
+          $messages = array();
+          $messages[] = pht(
+            'You must provide multi-factor credentials to comment or make '.
+            'changes, but you do not have multi-factor authentication '.
+            'configured on your account.');
+          $messages[] = pht(
+            'To continue, configure multi-factor authentication in Settings.');
+
+          return id(new PHUIInfoView())
+            ->setSeverity(PHUIInfoView::SEVERITY_MFA)
+            ->setErrors($messages);
+        }
+      }
+    }
+
     $data = array();
 
     $comment = $this->renderCommentPanel();
@@ -226,7 +253,7 @@ class PhabricatorApplicationTransactionCommentView extends AphrontView {
     }
 
     require_celerity_resource('phui-comment-form-css');
-    $image_uri = $user->getProfileImageURI();
+    $image_uri = $viewer->getProfileImageURI();
     $image = phutil_tag(
       'div',
       array(
@@ -388,6 +415,17 @@ class PhabricatorApplicationTransactionCommentView extends AphrontView {
         $form->appendChild($info_view);
       }
 
+      if ($this->getRequiresMFA()) {
+        $message = pht(
+          'You will be required to provide multi-factor credentials to '.
+          'comment or make changes.');
+
+        $form->appendChild(
+          id(new PHUIInfoView())
+            ->setSeverity(PHUIInfoView::SEVERITY_MFA)
+            ->setErrors(array($message)));
+      }
+
       $form->appendChild($invisi_bar);
       $form->addClass('phui-comment-has-actions');