diff --git a/src/applications/harbormaster/conduit/HarbormasterSendMessageConduitAPIMethod.php b/src/applications/harbormaster/conduit/HarbormasterSendMessageConduitAPIMethod.php
--- a/src/applications/harbormaster/conduit/HarbormasterSendMessageConduitAPIMethod.php
+++ b/src/applications/harbormaster/conduit/HarbormasterSendMessageConduitAPIMethod.php
@@ -9,18 +9,222 @@
 
   public function getMethodSummary() {
     return pht(
-      'Send a message about the status of a build target to Harbormaster, '.
-      'notifying the application of build results in an external system.');
+      'Modify running builds, and report build results.');
   }
 
   public function getMethodDescription() {
+    return pht(<<<EOREMARKUP
+Pause, abort, restart, and report results for builds.
+EOREMARKUP
+      );
+  }
+
+  protected function newDocumentationPages(PhabricatorUser $viewer) {
+    $pages = array();
+
+    $pages[] = $this->newSendingDocumentationBoxPage($viewer);
+    $pages[] = $this->newBuildsDocumentationBoxPage($viewer);
+    $pages[] = $this->newCommandsDocumentationBoxPage($viewer);
+    $pages[] = $this->newTargetsDocumentationBoxPage($viewer);
+    $pages[] = $this->newUnitDocumentationBoxPage($viewer);
+    $pages[] = $this->newLintDocumentationBoxPage($viewer);
+
+    return $pages;
+  }
+
+  private function newSendingDocumentationBoxPage(PhabricatorUser $viewer) {
+    $title = pht('Sending Messages');
+    $content = pht(<<<EOREMARKUP
+Harbormaster build objects work somewhat differently from objects in many other
+applications. Most application objects can be edited directly using synchronous
+APIs (like `maniphest.edit`, `differential.revision.edit`, and so on).
+
+However, builds require long-running background processing and Habormaster
+objects have a more complex lifecycle than most other application objects and
+may spend significant periods of time locked by daemon processes during build
+execition. A synchronous edit might need to wait an arbitrarily long amount of
+time for this lock to become available so the edit could be applied.
+
+Additionally, some edits may also require an arbitrarily long amount of time to
+//complete//. For example, aborting a build may execute cleanup steps which
+take minutes (or even hours) to complete.
+
+Since a synchronous API could not guarantee it could return results to the
+caller in a reasonable amount of time, the edit API for Harbormaster build
+objects is asynchronous: to update a Harbormaster build or build target, use
+this API (`harbormaster.sendmessage`) to send it a message describing an edit
+you would like to effect or additional information you want to provide.
+The message will be processed by the daemons once the build or target reaches
+a suitable state to receive messages.
+
+Select an object to send a message to using the `receiver` parameter. This
+API method can send messages to multiple types of objects:
+
+<table>
+  <tr>
+    <th>Object Type</th>
+    <th>PHID Example</th>
+    <th>Description</th>
+  </tr>
+  <tr>
+    <td>Harbormaster Buildable</td>
+    <td>`PHID-HMBB-...`</td>
+    <td>%s</td>
+  </tr>
+  <tr>
+    <td>Harbormaster Build</td>
+    <td>`PHID-HMBD-...`</td>
+    <td>%s</td>
+  </tr>
+  <tr>
+    <td>Harbormaster Build Target</td>
+    <td>`PHID-HMBT-...`</td>
+    <td>%s</td>
+  </tr>
+</table>
+
+See below for specifics on sending messages to different object types.
+EOREMARKUP
+      ,
+      pht(
+        'Buildables may receive control commands like "abort" and "restart". '.
+        'Sending a control command to a Buildable is the same as sending it '.
+        'to each Build for the Buildable.'),
+      pht(
+        'Builds may receive control commands like "pause", "resume", "abort", '.
+        'and "restart".'),
+      pht(
+        'Build Targets may receive build status and result messages, like '.
+        '"pass" or "fail".'));
+
+    $content = $this->newRemarkupDocumentationView($content);
+
+    return $this->newDocumentationBoxPage($viewer, $title, $content)
+      ->setAnchor('sending')
+      ->setIconIcon('fa-envelope-o');
+  }
+
+  private function newBuildsDocumentationBoxPage(PhabricatorUser $viewer) {
+    $title = pht('Updating Builds');
+
+    $content = pht(<<<EOREMARKUP
+You can use this method (`harbormaster.sendmessage`) to send control commands
+to Buildables and Builds.
+
+Specify the Build or Buildable to receive the control command by providing its
+PHID in the `receiver` parameter.
+
+Sending a control command to a Buildable has the same effect as sending it to
+each Build for the Buildable. For example, sending a "Pause" message to a
+Buildable will pause all builds for the Buildable (or at least attempt to).
+
+When sending control commands, the `unit` and `lint` parameters of this API
+method must be omitted. You can not report lint or unit results directly to
+a Build or Buildable, and can not report them alongside a control command.
+
+More broadly, you can not report build results directly to a Build or
+Buildable. Instead, report results to a Build Target.
+
+See below for a list of control commands.
+
+EOREMARKUP
+      );
+
+    $content = $this->newRemarkupDocumentationView($content);
+
+    return $this->newDocumentationBoxPage($viewer, $title, $content)
+      ->setAnchor('builds')
+      ->setIconIcon('fa-cubes');
+  }
+
+  private function newCommandsDocumentationBoxPage(PhabricatorUser $viewer) {
+    $messages = HarbormasterBuildMessageTransaction::getAllMessages();
+
+    $rows = array();
+
+    $rows[] = '<tr>';
+    $rows[] = '<th>'.pht('Message Type').'</th>';
+    $rows[] = '<th>'.pht('Description').'</th>';
+    $rows[] = '</tr>';
+
+    foreach ($messages as $message) {
+      $row = array();
+
+      $row[] = sprintf(
+        '<td>`%s`</td>',
+        $message->getHarbormasterBuildMessageType());
+
+      $row[] = sprintf(
+        '<td>%s</td>',
+        $message->getHarbormasterBuildMessageDescription());
+
+      $rows[] = sprintf(
+        '<tr>%s</tr>',
+        implode("\n", $row));
+    }
+
+    $message_table = sprintf(
+      '<table>%s</table>',
+      implode("\n", $rows));
+
+    $title = pht('Control Commands');
+
+    $content = pht(<<<EOREMARKUP
+You can use this method to send control commands to Buildables and Builds.
+
+This table summarizes which object types may receive control commands:
+
+<table>
+  <tr>
+    <th>Object Type</th>
+    <th>PHID Example</th>
+    <th />
+    <th>Description</th>
+  </tr>
+  <tr>
+    <td>Harbormaster Buildable</td>
+    <td>`PHID-HMBB-...`</td>
+    <td>{icon check color=green}</td>
+    <td>Buildables may receive control commands.</td>
+  </tr>
+  <tr>
+    <td>Harbormaster Build</td>
+    <td>`PHID-HMBD-...`</td>
+    <td>{icon check color=green}</td>
+    <td>Builds may receive control commands.</td>
+  </tr>
+  <tr>
+    <td>Harbormaster Build Target</td>
+    <td>`PHID-HMBT-...`</td>
+    <td>{icon times color=red}</td>
+    <td>You may **NOT** send control commands to build targets.</td>
+  </tr>
+</table>
+
+You can send these commands:
+
+%s
+
+To send a command message, specify the PHID of the object you would like to
+receive the message using the `receiver` parameter, and specify the message
+type using the `type` parameter.
+
+EOREMARKUP
+      ,
+      $message_table);
+
+    $content = $this->newRemarkupDocumentationView($content);
+
+    return $this->newDocumentationBoxPage($viewer, $title, $content)
+      ->setAnchor('commands')
+      ->setIconIcon('fa-exclamation-triangle');
+  }
+
+  private function newTargetsDocumentationBoxPage(PhabricatorUser $viewer) {
     $messages = HarbormasterMessageType::getAllMessages();
 
-    $head_type = pht('Constant');
-    $head_desc = pht('Description');
-    $head_key = pht('Key');
     $head_type = pht('Type');
-    $head_name = pht('Name');
+    $head_desc = pht('Description');
 
     $rows = array();
     $rows[] = "| {$head_type} | {$head_desc} |";
@@ -31,6 +235,84 @@
     }
     $message_table = implode("\n", $rows);
 
+    $content = pht(<<<EOREMARKUP
+If you run external builds, you can use this method to publish build results
+back into Harbormaster after the external system finishes work (or as it makes
+progress).
+
+To report build status or results, you must send a message to the appropriate
+Build Target. This table summarizes which object types may receive build status
+and result messages:
+
+<table>
+  <tr>
+    <th>Object Type</th>
+    <th>PHID Example</th>
+    <th />
+    <th>Description</th>
+  </tr>
+  <tr>
+    <td>Harbormaster Buildable</td>
+    <td>`PHID-HMBB-...`</td>
+    <td>{icon times color=red}</td>
+    <td>Buildables may **NOT** receive status or result messages.</td>
+  </tr>
+  <tr>
+    <td>Harbormaster Build</td>
+    <td>`PHID-HMBD-...`</td>
+    <td>{icon times color=red}</td>
+    <td>Builds may **NOT** receive status or result messages.</td>
+  </tr>
+  <tr>
+    <td>Harbormaster Build Target</td>
+    <td>`PHID-HMBT-...`</td>
+    <td>{icon check color=green}</td>
+    <td>Report build status and results to Build Targets.</td>
+  </tr>
+</table>
+
+The simplest way to use this method to report build results is to call it once
+after the build finishes with a `pass` or `fail` message. This will record the
+build result, and continue the next step in the build if the build was waiting
+for a result.
+
+When you send a status message about a build target, you can optionally include
+detailed `lint` or `unit` results alongside the message. See below for details.
+
+If you want to report intermediate results but a build hasn't completed yet,
+you can use the `work` message. This message doesn't have any direct effects,
+but allows you to send additional data to update the progress of the build
+target. The target will continue waiting for a completion message, but the UI
+will update to show the progress which has been made.
+
+When sending a message to a build target to report the status or results of
+a build, your message must include a `type` which describes the overall state
+of the build. For example, use `pass` to tell Harbormaster that a build target
+completed successfully.
+
+Supported message types are:
+
+%s
+
+EOREMARKUP
+      ,
+      $message_table);
+
+    $title = pht('Updating Build Targets');
+
+    $content = $this->newRemarkupDocumentationView($content);
+
+    return $this->newDocumentationBoxPage($viewer, $title, $content)
+      ->setAnchor('targets')
+      ->setIconIcon('fa-bullseye');
+  }
+
+  private function newUnitDocumentationBoxPage(PhabricatorUser $viewer) {
+    $head_key = pht('Key');
+    $head_desc = pht('Description');
+    $head_name = pht('Name');
+    $head_type = pht('Type');
+
     $rows = array();
     $rows[] = "| {$head_key} | {$head_type} | {$head_desc} |";
     $rows[] = '|-------------|--------------|--------------|';
@@ -55,6 +337,64 @@
     }
     $result_table = implode("\n", $rows);
 
+    $valid_unit = array(
+      array(
+        'name' => 'PassingTest',
+        'result' => ArcanistUnitTestResult::RESULT_PASS,
+      ),
+      array(
+        'name' => 'FailingTest',
+        'result' => ArcanistUnitTestResult::RESULT_FAIL,
+      ),
+    );
+
+    $json = new PhutilJSON();
+    $valid_unit = $json->encodeAsList($valid_unit);
+
+
+    $title = pht('Reporting Unit Results');
+
+    $content = pht(<<<EOREMARKUP
+You can report test results when updating the state of a build target. The
+simplest way to do this is to report all the results alongside a `pass` or
+`fail` message, but you can also send a `work` message to report intermediate
+results.
+
+
+To provide unit test results, pass a list of results in the `unit`
+parameter. Each result should be a dictionary with these keys:
+
+%s
+
+The `result` parameter recognizes these test results:
+
+%s
+
+This is a simple, valid value for the `unit` parameter. It reports one passing
+test and one failing test:
+
+```lang=json
+%s
+```
+EOREMARKUP
+      ,
+      $unit_table,
+      $result_table,
+      $valid_unit);
+
+    $content = $this->newRemarkupDocumentationView($content);
+
+    return $this->newDocumentationBoxPage($viewer, $title, $content)
+      ->setAnchor('unit');
+  }
+
+  private function newLintDocumentationBoxPage(PhabricatorUser $viewer) {
+
+    $head_key = pht('Key');
+    $head_desc = pht('Description');
+    $head_name = pht('Name');
+    $head_type = pht('Type');
+
     $rows = array();
     $rows[] = "| {$head_key} | {$head_type} | {$head_desc} |";
     $rows[] = '|-------------|--------------|--------------|';
@@ -76,17 +416,6 @@
     }
     $severity_table = implode("\n", $rows);
 
-    $valid_unit = array(
-      array(
-        'name' => 'PassingTest',
-        'result' => ArcanistUnitTestResult::RESULT_PASS,
-      ),
-      array(
-        'name' => 'FailingTest',
-        'result' => ArcanistUnitTestResult::RESULT_FAIL,
-      ),
-    );
-
     $valid_lint = array(
       array(
         'name' => pht('Syntax Error'),
@@ -109,104 +438,58 @@
     );
 
     $json = new PhutilJSON();
-    $valid_unit = $json->encodeAsList($valid_unit);
     $valid_lint = $json->encodeAsList($valid_lint);
 
-    return pht(
-      "Send a message about the status of a build target to Harbormaster, ".
-      "notifying the application of build results in an external system.".
-      "\n\n".
-      "Sending Messages\n".
-      "================\n".
-      "If you run external builds, you can use this method to publish build ".
-      "results back into Harbormaster after the external system finishes work ".
-      "or as it makes progress.".
-      "\n\n".
-      "The simplest way to use this method is to call it once after the ".
-      "build finishes with a `pass` or `fail` message. This will record the ".
-      "build result, and continue the next step in the build if the build was ".
-      "waiting for a result.".
-      "\n\n".
-      "When you send a status message about a build target, you can ".
-      "optionally include detailed `lint` or `unit` results alongside the ".
-      "message. See below for details.".
-      "\n\n".
-      "If you want to report intermediate results but a build hasn't ".
-      "completed yet, you can use the `work` message. This message doesn't ".
-      "have any direct effects, but allows you to send additional data to ".
-      "update the progress of the build target. The target will continue ".
-      "waiting for a completion message, but the UI will update to show the ".
-      "progress which has been made.".
-      "\n\n".
-      "Message Types\n".
-      "=============\n".
-      "When you send Harbormaster a message, you must include a `type`, ".
-      "which describes the overall state of the build. For example, use ".
-      "`pass` to tell Harbormaster that a build completed successfully.".
-      "\n\n".
-      "Supported message types are:".
-      "\n\n".
-      "%s".
-      "\n\n".
-      "Unit Results\n".
-      "============\n".
-      "You can report test results alongside a message. The simplest way to ".
-      "do this is to report all the results alongside a `pass` or `fail` ".
-      "message, but you can also send a `work` message to report intermediate ".
-      "results.\n\n".
-      "To provide unit test results, pass a list of results in the `unit` ".
-      "parameter. Each result should be a dictionary with these keys:".
-      "\n\n".
-      "%s".
-      "\n\n".
-      "The `result` parameter recognizes these test results:".
-      "\n\n".
-      "%s".
-      "\n\n".
-      "This is a simple, valid value for the `unit` parameter. It reports ".
-      "one passing test and one failing test:\n\n".
-      "\n\n".
-      "```lang=json\n".
-      "%s".
-      "```".
-      "\n\n".
-      "Lint Results\n".
-      "============\n".
-      "Like unit test results, you can report lint results alongside a ".
-      "message. The `lint` parameter should contain results as a list of ".
-      "dictionaries with these keys:".
-      "\n\n".
-      "%s".
-      "\n\n".
-      "The `severity` parameter recognizes these severity levels:".
-      "\n\n".
-      "%s".
-      "\n\n".
-      "This is a simple, valid value for the `lint` parameter. It reports one ".
-      "error and one warning:".
-      "\n\n".
-      "```lang=json\n".
-      "%s".
-      "```".
-      "\n\n",
-      $message_table,
-      $unit_table,
-      $result_table,
-      $valid_unit,
+    $title = pht('Reporting Lint Results');
+    $content = pht(<<<EOREMARKUP
+Like unit test results, you can report lint results when updating the state
+of a build target. The `lint` parameter should contain results as a list of
+dictionaries with these keys:
+
+%s
+
+The `severity` parameter recognizes these severity levels:
+
+%s
+
+This is a simple, valid value for the `lint` parameter. It reports one error
+and one warning:
+
+```lang=json
+%s
+```
+
+EOREMARKUP
+      ,
       $lint_table,
       $severity_table,
       $valid_lint);
+
+    $content = $this->newRemarkupDocumentationView($content);
+
+    return $this->newDocumentationBoxPage($viewer, $title, $content)
+      ->setAnchor('lint');
   }
 
   protected function defineParamTypes() {
     $messages = HarbormasterMessageType::getAllMessages();
+
+    $more_messages = HarbormasterBuildMessageTransaction::getAllMessages();
+    $more_messages = mpull($more_messages, 'getHarbormasterBuildMessageType');
+
+    $messages = array_merge($messages, $more_messages);
+    $messages = array_unique($messages);
+
+    sort($messages);
+
     $type_const = $this->formatStringConstants($messages);
 
     return array(
-      'buildTargetPHID' => 'required phid',
+      'receiver' => 'required string|phid',
       'type' => 'required '.$type_const,
       'unit' => 'optional list<wild>',
       'lint' => 'optional list<wild>',
+      'buildTargetPHID' => 'deprecated optional phid',
     );
   }
 
@@ -215,19 +498,90 @@
   }
 
   protected function execute(ConduitAPIRequest $request) {
-    $viewer = $request->getUser();
+    $viewer = $request->getViewer();
+
+    $receiver_name = $request->getValue('receiver');
 
     $build_target_phid = $request->getValue('buildTargetPHID');
+    if ($build_target_phid !== null) {
+      if ($receiver_name === null) {
+        $receiver_name = $build_target_phid;
+      } else {
+        throw new Exception(
+          pht(
+            'Call specifies both "receiver" and "buildTargetPHID". '.
+            'When using the modern "receiver" parameter, omit the '.
+            'deprecated "buildTargetPHID" parameter.'));
+      }
+    }
+
+    if (!strlen($receiver_name)) {
+      throw new Exception(
+        pht(
+          'Call omits required "receiver" parameter. Specify the PHID '.
+          'of the object you want to send a message to.'));
+    }
+
     $message_type = $request->getValue('type');
+    if (!strlen($message_type)) {
+      throw new Exception(
+        pht(
+          'Call omits required "type" parameter. Specify the type of '.
+          'message you want to send.'));
+    }
 
-    $build_target = id(new HarbormasterBuildTargetQuery())
+    $receiver_object = id(new PhabricatorObjectQuery())
       ->setViewer($viewer)
-      ->withPHIDs(array($build_target_phid))
+      ->withNames(array($receiver_name))
       ->executeOne();
-    if (!$build_target) {
-      throw new Exception(pht('No such build target!'));
+    if (!$receiver_object) {
+      throw new Exception(
+        pht(
+          'Unable to load object "%s" to receive message.',
+          $receiver_name));
+    }
+
+    $is_target = ($receiver_object instanceof HarbormasterBuildTarget);
+    if ($is_target) {
+      return $this->sendToTarget($request, $message_type, $receiver_object);
+    }
+
+    if ($request->getValue('unit') !== null) {
+      throw new Exception(
+        pht(
+          'Call includes "unit" parameter. This parameter must be omitted '.
+          'when the receiver is not a Build Target.'));
+    }
+
+    if ($request->getValue('lint') !== null) {
+      throw new Exception(
+        pht(
+          'Call includes "lint" parameter. This parameter must be omitted '.
+          'when the receiver is not a Build Target.'));
+    }
+
+    $is_build = ($receiver_object instanceof HarbormasterBuild);
+    if ($is_build) {
+      return $this->sendToBuild($request, $message_type, $receiver_object);
+    }
+
+    $is_buildable = ($receiver_object instanceof HarbormasterBuildable);
+    if ($is_buildable) {
+      return $this->sendToBuildable($request, $message_type, $receiver_object);
     }
 
+    throw new Exception(
+      pht(
+        'Receiver object (of class "%s") is not a valid receiver.',
+        get_class($receiver_object)));
+  }
+
+  private function sendToTarget(
+    ConduitAPIRequest $request,
+    $message_type,
+    HarbormasterBuildTarget $build_target) {
+    $viewer = $request->getViewer();
+
     $save = array();
 
     $lint_messages = $request->getValue('lint', array());
@@ -270,4 +624,67 @@
     return null;
   }
 
+  private function sendToBuild(
+    ConduitAPIRequest $request,
+    $message_type,
+    HarbormasterBuild $build) {
+    $viewer = $request->getViewer();
+
+    $xaction =
+      HarbormasterBuildMessageTransaction::getTransactionObjectForMessageType(
+        $message_type);
+    if (!$xaction) {
+      throw new Exception(
+        pht(
+          'Message type "%s" is not supported.',
+          $message_type));
+    }
+
+    // NOTE: This is a slightly weaker check than we perform in the web UI.
+    // We allow API callers to send a "pause" message to a pausing build,
+    // for example, even though the message will have no effect.
+    $xaction->assertCanApplyMessage($viewer, $build);
+
+    $build->sendMessage($viewer, $xaction->getHarbormasterBuildMessageType());
+  }
+
+  private function sendToBuildable(
+    ConduitAPIRequest $request,
+    $message_type,
+    HarbormasterBuildable $buildable) {
+    $viewer = $request->getViewer();
+
+    $xaction =
+      HarbormasterBuildMessageTransaction::getTransactionObjectForMessageType(
+        $message_type);
+    if (!$xaction) {
+      throw new Exception(
+        pht(
+          'Message type "%s" is not supported.',
+          $message_type));
+    }
+
+    // Reload the Buildable to load Builds.
+    $buildable = id(new HarbormasterBuildableQuery())
+      ->setViewer($viewer)
+      ->withIDs(array($buildable->getID()))
+      ->needBuilds(true)
+      ->executeOne();
+
+    $can_send = array();
+    foreach ($buildable->getBuilds() as $build) {
+      if ($xaction->canApplyMessage($viewer, $build)) {
+        $can_send[] = $build;
+      }
+    }
+
+    // NOTE: This doesn't actually apply a transaction to the Buildable,
+    // but that transaction is purely informational and should probably be
+    // implemented as a Message.
+
+    foreach ($can_send as $build) {
+      $build->sendMessage($viewer, $xaction->getHarbormasterBuildMessageType());
+    }
+  }
+
 }
diff --git a/src/applications/harbormaster/exception/HarbormasterRestartException.php b/src/applications/harbormaster/exception/HarbormasterRestartException.php
--- a/src/applications/harbormaster/exception/HarbormasterRestartException.php
+++ b/src/applications/harbormaster/exception/HarbormasterRestartException.php
@@ -9,7 +9,11 @@
     $this->setTitle($title);
     $this->appendParagraph($body);
 
-    parent::__construct($title);
+    parent::__construct(
+      pht(
+        '%s: %s',
+        $title,
+        $body));
   }
 
   public function setTitle($title) {
diff --git a/src/applications/harbormaster/xaction/build/HarbormasterBuildMessageAbortTransaction.php b/src/applications/harbormaster/xaction/build/HarbormasterBuildMessageAbortTransaction.php
--- a/src/applications/harbormaster/xaction/build/HarbormasterBuildMessageAbortTransaction.php
+++ b/src/applications/harbormaster/xaction/build/HarbormasterBuildMessageAbortTransaction.php
@@ -27,6 +27,10 @@
       'Progress on this build will be discarded. Really abort build?');
   }
 
+  public function getHarbormasterBuildMessageDescription() {
+    return pht('Abort the build, discarding progress.');
+  }
+
   public function newBuildableConfirmPromptTitle(
     array $builds,
     array $sendable) {
diff --git a/src/applications/harbormaster/xaction/build/HarbormasterBuildMessagePauseTransaction.php b/src/applications/harbormaster/xaction/build/HarbormasterBuildMessagePauseTransaction.php
--- a/src/applications/harbormaster/xaction/build/HarbormasterBuildMessagePauseTransaction.php
+++ b/src/applications/harbormaster/xaction/build/HarbormasterBuildMessagePauseTransaction.php
@@ -28,6 +28,11 @@
       'complete. You can resume the build later.');
   }
 
+
+  public function getHarbormasterBuildMessageDescription() {
+    return pht('Pause the build.');
+  }
+
   public function newBuildableConfirmPromptTitle(
     array $builds,
     array $sendable) {
diff --git a/src/applications/harbormaster/xaction/build/HarbormasterBuildMessageRestartTransaction.php b/src/applications/harbormaster/xaction/build/HarbormasterBuildMessageRestartTransaction.php
--- a/src/applications/harbormaster/xaction/build/HarbormasterBuildMessageRestartTransaction.php
+++ b/src/applications/harbormaster/xaction/build/HarbormasterBuildMessageRestartTransaction.php
@@ -28,6 +28,11 @@
       'Side effects of the build will occur again. Really restart build?');
   }
 
+
+  public function getHarbormasterBuildMessageDescription() {
+    return pht('Restart the build, discarding all progress.');
+  }
+
   public function newBuildableConfirmPromptTitle(
     array $builds,
     array $sendable) {
diff --git a/src/applications/harbormaster/xaction/build/HarbormasterBuildMessageResumeTransaction.php b/src/applications/harbormaster/xaction/build/HarbormasterBuildMessageResumeTransaction.php
--- a/src/applications/harbormaster/xaction/build/HarbormasterBuildMessageResumeTransaction.php
+++ b/src/applications/harbormaster/xaction/build/HarbormasterBuildMessageResumeTransaction.php
@@ -27,6 +27,10 @@
       'Work will continue on the build. Really resume?');
   }
 
+  public function getHarbormasterBuildMessageDescription() {
+    return pht('Resume work on a previously paused build.');
+  }
+
   public function newBuildableConfirmPromptTitle(
     array $builds,
     array $sendable) {
@@ -77,7 +81,7 @@
           'You can not resume a build that uses an autoplan.'));
     }
 
-    if (!$build->isPaused()) {
+    if (!$build->isPaused() && !$build->isPausing()) {
       throw new HarbormasterRestartException(
         pht('Unable to Resume Build'),
         pht(
diff --git a/src/applications/harbormaster/xaction/build/HarbormasterBuildMessageTransaction.php b/src/applications/harbormaster/xaction/build/HarbormasterBuildMessageTransaction.php
--- a/src/applications/harbormaster/xaction/build/HarbormasterBuildMessageTransaction.php
+++ b/src/applications/harbormaster/xaction/build/HarbormasterBuildMessageTransaction.php
@@ -8,6 +8,7 @@
   }
 
   abstract public function getHarbormasterBuildMessageName();
+  abstract public function getHarbormasterBuildMessageDescription();
   abstract public function getHarbormasterBuildableMessageName();
   abstract public function getHarbormasterBuildableMessageEffect();
 
@@ -42,12 +43,18 @@
     );
   }
 
-  final public static function getTransactionObjectForMessageType(
-    $message_type) {
+  final public static function getAllMessages() {
     $message_xactions = id(new PhutilClassMapQuery())
       ->setAncestorClass(__CLASS__)
       ->execute();
 
+    return $message_xactions;
+  }
+
+  final public static function getTransactionObjectForMessageType(
+    $message_type) {
+    $message_xactions = self::getAllMessages();
+
     foreach ($message_xactions as $message_xaction) {
       $xaction_type = $message_xaction->getHarbormasterBuildMessageType();
       if ($xaction_type === $message_type) {