diff --git a/src/__phutil_library_map__.php b/src/__phutil_library_map__.php
--- a/src/__phutil_library_map__.php
+++ b/src/__phutil_library_map__.php
@@ -1094,7 +1094,6 @@
     'HarbormasterBuildableTransactionQuery' => 'applications/harbormaster/query/HarbormasterBuildableTransactionQuery.php',
     'HarbormasterBuildableViewController' => 'applications/harbormaster/controller/HarbormasterBuildableViewController.php',
     'HarbormasterBuiltinBuildStepGroup' => 'applications/harbormaster/stepgroup/HarbormasterBuiltinBuildStepGroup.php',
-    'HarbormasterCommandBuildStepImplementation' => 'applications/harbormaster/step/HarbormasterCommandBuildStepImplementation.php',
     'HarbormasterConduitAPIMethod' => 'applications/harbormaster/conduit/HarbormasterConduitAPIMethod.php',
     'HarbormasterController' => 'applications/harbormaster/controller/HarbormasterController.php',
     'HarbormasterCreateArtifactConduitAPIMethod' => 'applications/harbormaster/conduit/HarbormasterCreateArtifactConduitAPIMethod.php',
@@ -1108,7 +1107,6 @@
     'HarbormasterFileArtifact' => 'applications/harbormaster/artifact/HarbormasterFileArtifact.php',
     'HarbormasterHTTPRequestBuildStepImplementation' => 'applications/harbormaster/step/HarbormasterHTTPRequestBuildStepImplementation.php',
     'HarbormasterHostArtifact' => 'applications/harbormaster/artifact/HarbormasterHostArtifact.php',
-    'HarbormasterLeaseHostBuildStepImplementation' => 'applications/harbormaster/step/HarbormasterLeaseHostBuildStepImplementation.php',
     'HarbormasterLeaseWorkingCopyBuildStepImplementation' => 'applications/harbormaster/step/HarbormasterLeaseWorkingCopyBuildStepImplementation.php',
     'HarbormasterLintMessagesController' => 'applications/harbormaster/controller/HarbormasterLintMessagesController.php',
     'HarbormasterLintPropertyView' => 'applications/harbormaster/view/HarbormasterLintPropertyView.php',
@@ -5259,7 +5257,6 @@
     'HarbormasterBuildableTransactionQuery' => 'PhabricatorApplicationTransactionQuery',
     'HarbormasterBuildableViewController' => 'HarbormasterController',
     'HarbormasterBuiltinBuildStepGroup' => 'HarbormasterBuildStepGroup',
-    'HarbormasterCommandBuildStepImplementation' => 'HarbormasterBuildStepImplementation',
     'HarbormasterConduitAPIMethod' => 'ConduitAPIMethod',
     'HarbormasterController' => 'PhabricatorController',
     'HarbormasterCreateArtifactConduitAPIMethod' => 'HarbormasterConduitAPIMethod',
@@ -5273,7 +5270,6 @@
     'HarbormasterFileArtifact' => 'HarbormasterArtifact',
     'HarbormasterHTTPRequestBuildStepImplementation' => 'HarbormasterBuildStepImplementation',
     'HarbormasterHostArtifact' => 'HarbormasterDrydockLeaseArtifact',
-    'HarbormasterLeaseHostBuildStepImplementation' => 'HarbormasterBuildStepImplementation',
     'HarbormasterLeaseWorkingCopyBuildStepImplementation' => 'HarbormasterBuildStepImplementation',
     'HarbormasterLintMessagesController' => 'HarbormasterController',
     'HarbormasterLintPropertyView' => 'AphrontView',
diff --git a/src/applications/harbormaster/controller/HarbormasterPlanViewController.php b/src/applications/harbormaster/controller/HarbormasterPlanViewController.php
--- a/src/applications/harbormaster/controller/HarbormasterPlanViewController.php
+++ b/src/applications/harbormaster/controller/HarbormasterPlanViewController.php
@@ -105,31 +105,31 @@
         $i++;
       }
 
+      $step_id = $step->getID();
+      $view_uri = $this->getApplicationURI("step/view/{$step_id}/");
+
+      $item = id(new PHUIObjectItemView())
+        ->setObjectName(pht('Step %d.%d', $depth, $i))
+        ->setHeader($step->getName())
+        ->setHref($view_uri);
+
+      $step_list->addItem($item);
+
       $implementation = null;
       try {
         $implementation = $step->getStepImplementation();
       } catch (Exception $ex) {
         // We can't initialize the implementation. This might be because
         // it's been renamed or no longer exists.
-        $item = id(new PHUIObjectItemView())
-          ->setObjectName(pht('Step %d.%d', $depth, $i))
-          ->setHeader(pht('Unknown Implementation'))
+        $item
           ->setStatusIcon('fa-warning red')
           ->addAttribute(pht(
             'This step has an invalid implementation (%s).',
             $step->getClassName()));
-        $step_list->addItem($item);
         continue;
       }
-      $item = id(new PHUIObjectItemView())
-        ->setObjectName(pht('Step %d.%d', $depth, $i))
-        ->setHeader($step->getName());
 
       $item->addAttribute($implementation->getDescription());
-
-      $step_id = $step->getID();
-
-      $view_uri = $this->getApplicationURI("step/view/{$step_id}/");
       $item->setHref($view_uri);
 
       $depends = $step->getStepImplementation()->getDependencies($step);
diff --git a/src/applications/harbormaster/controller/HarbormasterStepViewController.php b/src/applications/harbormaster/controller/HarbormasterStepViewController.php
--- a/src/applications/harbormaster/controller/HarbormasterStepViewController.php
+++ b/src/applications/harbormaster/controller/HarbormasterStepViewController.php
@@ -18,8 +18,6 @@
     $plan_id = $plan->getID();
     $plan_uri = $this->getApplicationURI("plan/{$plan_id}/");
 
-    $implementation = $step->getStepImplementation();
-
     $field_list = PhabricatorCustomField::getObjectFields(
       $step,
       PhabricatorCustomField::ROLE_VIEW);
@@ -65,6 +63,25 @@
       ->setUser($viewer)
       ->setObject($step);
 
+    try {
+      $implementation = $step->getStepImplementation();
+    } catch (Exception $ex) {
+      $implementation = null;
+    }
+
+    if ($implementation) {
+      $type = $implementation->getName();
+    } else {
+      $type = phutil_tag(
+        'em',
+        array(),
+        pht(
+          'Invalid Implementation ("%s")!',
+          $step->getClassName()));
+    }
+
+    $view->addProperty(pht('Step Type'), $type);
+
     $view->addProperty(
       pht('Created'),
       phabricator_datetime($step->getDateCreated(), $viewer));
diff --git a/src/applications/harbormaster/customfield/HarbormasterBuildStepCoreCustomField.php b/src/applications/harbormaster/customfield/HarbormasterBuildStepCoreCustomField.php
--- a/src/applications/harbormaster/customfield/HarbormasterBuildStepCoreCustomField.php
+++ b/src/applications/harbormaster/customfield/HarbormasterBuildStepCoreCustomField.php
@@ -9,7 +9,12 @@
   }
 
   public function createFields($object) {
-    $impl = $object->getStepImplementation();
+    try {
+      $impl = $object->getStepImplementation();
+    } catch (Exception $ex) {
+      return array();
+    }
+
     $specs = $impl->getFieldSpecifications();
 
     if ($impl->supportsWaitForMessage()) {
diff --git a/src/applications/harbormaster/engine/HarbormasterBuildGraph.php b/src/applications/harbormaster/engine/HarbormasterBuildGraph.php
--- a/src/applications/harbormaster/engine/HarbormasterBuildGraph.php
+++ b/src/applications/harbormaster/engine/HarbormasterBuildGraph.php
@@ -48,7 +48,12 @@
     $map = array();
     foreach ($nodes as $node) {
       $step = $this->stepMap[$node];
-      $deps = $step->getStepImplementation()->getDependencies($step);
+
+      try {
+        $deps = $step->getStepImplementation()->getDependencies($step);
+      } catch (Exception $ex) {
+        $deps = array();
+      }
 
       $map[$node] = array();
       foreach ($deps as $dep) {
diff --git a/src/applications/harbormaster/step/HarbormasterCommandBuildStepImplementation.php b/src/applications/harbormaster/step/HarbormasterCommandBuildStepImplementation.php
deleted file mode 100644
--- a/src/applications/harbormaster/step/HarbormasterCommandBuildStepImplementation.php
+++ /dev/null
@@ -1,149 +0,0 @@
-<?php
-
-final class HarbormasterCommandBuildStepImplementation
-  extends HarbormasterBuildStepImplementation {
-
-  private $platform;
-
-  public function getName() {
-    return pht('Run Command');
-  }
-
-  public function getGenericDescription() {
-    return pht('Run a command on Drydock host.');
-  }
-
-  public function getBuildStepGroupKey() {
-    return HarbormasterPrototypeBuildStepGroup::GROUPKEY;
-  }
-
-  public function getDescription() {
-    return pht(
-      'Run command %s on host %s.',
-      $this->formatSettingForDescription('command'),
-      $this->formatSettingForDescription('hostartifact'));
-  }
-
-  public function escapeCommand($pattern, array $args) {
-    array_unshift($args, $pattern);
-
-    $mode = PhutilCommandString::MODE_DEFAULT;
-    if ($this->platform == 'windows') {
-      $mode = PhutilCommandString::MODE_POWERSHELL;
-    }
-
-    return id(new PhutilCommandString($args))
-      ->setEscapingMode($mode);
-  }
-
-  public function execute(
-    HarbormasterBuild $build,
-    HarbormasterBuildTarget $build_target) {
-    $viewer = PhabricatorUser::getOmnipotentUser();
-
-    $settings = $this->getSettings();
-    $variables = $build_target->getVariables();
-
-    $artifact = $build_target->loadArtifact($settings['hostartifact']);
-    $impl = $artifact->getArtifactImplementation();
-    $lease = $impl->loadArtifactLease($viewer);
-
-    $this->platform = $lease->getAttribute('platform');
-
-    $command = $this->mergeVariables(
-      array($this, 'escapeCommand'),
-      $settings['command'],
-      $variables);
-
-    $this->platform = null;
-
-    $interface = $lease->getInterface('command');
-
-    $future = $interface->getExecFuture('%C', $command);
-
-    $log_stdout = $build->createLog($build_target, 'remote', 'stdout');
-    $log_stderr = $build->createLog($build_target, 'remote', 'stderr');
-
-    $start_stdout = $log_stdout->start();
-    $start_stderr = $log_stderr->start();
-
-    $build_update = 5;
-
-    // Read the next amount of available output every second.
-    $futures = new FutureIterator(array($future));
-    foreach ($futures->setUpdateInterval(1) as $key => $future_iter) {
-      if ($future_iter === null) {
-
-        // Check to see if we should abort.
-        if ($build_update <= 0) {
-          $build->reload();
-          if ($this->shouldAbort($build, $build_target)) {
-            $future->resolveKill();
-            throw new HarbormasterBuildAbortedException();
-          } else {
-            $build_update = 5;
-          }
-        } else {
-          $build_update -= 1;
-        }
-
-        // Command is still executing.
-
-        // Read more data as it is available.
-        list($stdout, $stderr) = $future->read();
-        $log_stdout->append($stdout);
-        $log_stderr->append($stderr);
-        $future->discardBuffers();
-      } else {
-        // Command execution is complete.
-
-        // Get the return value so we can log that as well.
-        list($err) = $future->resolve();
-
-        // Retrieve the last few bits of information.
-        list($stdout, $stderr) = $future->read();
-        $log_stdout->append($stdout);
-        $log_stderr->append($stderr);
-        $future->discardBuffers();
-
-        break;
-      }
-    }
-
-    $log_stdout->finalize($start_stdout);
-    $log_stderr->finalize($start_stderr);
-
-    if ($err) {
-      throw new HarbormasterBuildFailureException();
-    }
-  }
-
-  public function getArtifactInputs() {
-    return array(
-      array(
-        'name' => pht('Run on Host'),
-        'key' => $this->getSetting('hostartifact'),
-        'type' => HarbormasterHostArtifact::ARTIFACTCONST,
-      ),
-    );
-  }
-
-  public function getFieldSpecifications() {
-    return array(
-      'command' => array(
-        'name' => pht('Command'),
-        'type' => 'text',
-        'required' => true,
-        'caption' => pht(
-          "Under Windows, this is executed under PowerShell. ".
-          "Under UNIX, this is executed using the user's shell."),
-      ),
-      'hostartifact' => array(
-        'name' => pht('Host'),
-        'type' => 'text',
-        'required' => true,
-      ),
-    );
-  }
-
-}
diff --git a/src/applications/harbormaster/step/HarbormasterLeaseHostBuildStepImplementation.php b/src/applications/harbormaster/step/HarbormasterLeaseHostBuildStepImplementation.php
deleted file mode 100644
--- a/src/applications/harbormaster/step/HarbormasterLeaseHostBuildStepImplementation.php
+++ /dev/null
@@ -1,74 +0,0 @@
-<?php
-
-final class HarbormasterLeaseHostBuildStepImplementation
-  extends HarbormasterBuildStepImplementation {
-
-  public function getName() {
-    return pht('Lease Host');
-  }
-
-  public function getGenericDescription() {
-    return pht('Obtain a lease on a Drydock host for performing builds.');
-  }
-
-  public function getBuildStepGroupKey() {
-    return HarbormasterPrototypeBuildStepGroup::GROUPKEY;
-  }
-
-  public function execute(
-    HarbormasterBuild $build,
-    HarbormasterBuildTarget $build_target) {
-
-    $settings = $this->getSettings();
-
-    // Create the lease.
-    $lease = id(new DrydockLease())
-      ->setResourceType('host')
-      ->setOwnerPHID($build_target->getPHID())
-      ->setAttributes(
-        array(
-          'platform' => $settings['platform'],
-        ))
-      ->queueForActivation();
-
-    // Wait until the lease is fulfilled.
-    // TODO: This will throw an exception if the lease can't be fulfilled;
-    // we should treat that as build failure not build error.
-    $lease->waitUntilActive();
-
-    // Create the associated artifact.
-    $artifact = $build_target->createArtifact(
-      PhabricatorUser::getOmnipotentUser(),
-      $settings['name'],
-      HarbormasterHostArtifact::ARTIFACTCONST,
-      array(
-        'drydockLeasePHID' => $lease->getPHID(),
-      ));
-  }
-
-  public function getArtifactOutputs() {
-    return array(
-      array(
-        'name' => pht('Leased Host'),
-        'key' => $this->getSetting('name'),
-        'type' => HarbormasterHostArtifact::ARTIFACTCONST,
-      ),
-    );
-  }
-
-  public function getFieldSpecifications() {
-    return array(
-      'name' => array(
-        'name' => pht('Artifact Name'),
-        'type' => 'text',
-        'required' => true,
-      ),
-      'platform' => array(
-        'name' => pht('Platform'),
-        'type' => 'text',
-        'required' => true,
-      ),
-    );
-  }
-
-}