Index: resources/sql/patches/20131105.buildstep.sql
===================================================================
--- /dev/null
+++ resources/sql/patches/20131105.buildstep.sql
@@ -0,0 +1,11 @@
+CREATE TABLE {$NAMESPACE}_harbormaster.harbormaster_buildstep (
+  id INT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,
+  phid VARCHAR(64) NOT NULL COLLATE utf8_bin,
+  buildPlanPHID VARCHAR(64) NOT NULL COLLATE utf8_bin,
+  className VARCHAR(255) NOT NULL COLLATE utf8_bin,
+  details LONGTEXT CHARACTER SET utf8 COLLATE utf8_bin NOT NULL,
+  dateCreated INT UNSIGNED NOT NULL,
+  dateModified INT UNSIGNED NOT NULL,
+  KEY `key_plan` (buildPlanPHID),
+  UNIQUE KEY `key_phid` (phid)
+) ENGINE=InnoDB, COLLATE utf8_general_ci;
Index: src/__phutil_library_map__.php
===================================================================
--- src/__phutil_library_map__.php
+++ src/__phutil_library_map__.php
@@ -91,6 +91,7 @@
     'AphrontView' => 'view/AphrontView.php',
     'AphrontWebpageResponse' => 'aphront/response/AphrontWebpageResponse.php',
     'AuditActionMenuEventListener' => 'applications/audit/events/AuditActionMenuEventListener.php',
+    'BuildStepImplementation' => 'applications/harbormaster/step/BuildStepImplementation.php',
     'CelerityAPI' => 'infrastructure/celerity/CelerityAPI.php',
     'CelerityPhabricatorResourceController' => 'infrastructure/celerity/CelerityPhabricatorResourceController.php',
     'CelerityResourceController' => 'infrastructure/celerity/CelerityResourceController.php',
@@ -2195,6 +2196,7 @@
     'ReleephStatusFieldSpecification' => 'applications/releeph/field/specification/ReleephStatusFieldSpecification.php',
     'ReleephSummaryFieldSpecification' => 'applications/releeph/field/specification/ReleephSummaryFieldSpecification.php',
     'ReleephUserView' => 'applications/releeph/view/user/ReleephUserView.php',
+    'SleepBuildStepImplementation' => 'applications/harbormaster/step/SleepBuildStepImplementation.php',
     'SlowvoteEmbedView' => 'applications/slowvote/view/SlowvoteEmbedView.php',
     'SlowvoteRemarkupRule' => 'applications/slowvote/remarkup/SlowvoteRemarkupRule.php',
   ),
@@ -2872,7 +2874,11 @@
     'HarbormasterBuildPlanTransactionComment' => 'PhabricatorApplicationTransactionComment',
     'HarbormasterBuildPlanTransactionQuery' => 'PhabricatorApplicationTransactionQuery',
     'HarbormasterBuildQuery' => 'PhabricatorCursorPagedPolicyAwareQuery',
-    'HarbormasterBuildStep' => 'HarbormasterDAO',
+    'HarbormasterBuildStep' =>
+    array(
+      0 => 'HarbormasterDAO',
+      1 => 'PhabricatorPolicyInterface',
+    ),
     'HarbormasterBuildStepQuery' => 'PhabricatorCursorPagedPolicyAwareQuery',
     'HarbormasterBuildTarget' => 'HarbormasterDAO',
     'HarbormasterBuildTargetQuery' => 'PhabricatorCursorPagedPolicyAwareQuery',
@@ -4651,6 +4657,7 @@
     'ReleephStatusFieldSpecification' => 'ReleephFieldSpecification',
     'ReleephSummaryFieldSpecification' => 'ReleephFieldSpecification',
     'ReleephUserView' => 'AphrontView',
+    'SleepBuildStepImplementation' => 'BuildStepImplementation',
     'SlowvoteEmbedView' => 'AphrontView',
     'SlowvoteRemarkupRule' => 'PhabricatorRemarkupRuleObject',
   ),
Index: src/applications/harbormaster/query/HarbormasterBuildStepQuery.php
===================================================================
--- src/applications/harbormaster/query/HarbormasterBuildStepQuery.php
+++ src/applications/harbormaster/query/HarbormasterBuildStepQuery.php
@@ -5,6 +5,7 @@
 
   private $ids;
   private $phids;
+  private $buildPlanPHIDs;
 
   public function withIDs(array $ids) {
     $this->ids = $ids;
@@ -16,6 +17,11 @@
     return $this;
   }
 
+  public function withBuildPlanPHIDs(array $phids) {
+    $this->buildPlanPHIDs = $phids;
+    return $this;
+  }
+
   protected function loadPage() {
     $table = new HarbormasterBuildStep();
     $conn_r = $table->establishConnection('r');
@@ -48,11 +54,43 @@
         $this->phids);
     }
 
+    if ($this->buildPlanPHIDs) {
+      $where[] = qsprintf(
+        $conn_r,
+        'buildPlanPHID in (%Ls)',
+        $this->buildPlanPHIDs);
+    }
+
     $where[] = $this->buildPagingClause($conn_r);
 
     return $this->formatWhereClause($where);
   }
 
+  protected function willFilterPage(array $page) {
+    $plans = array();
+
+    $buildplan_phids = array_filter(mpull($page, 'getBuildPlanPHID'));
+    if ($buildplan_phids) {
+      $plans = id(new PhabricatorObjectQuery())
+        ->setViewer($this->getViewer())
+        ->withPHIDs($buildplan_phids)
+        ->setParentQuery($this)
+        ->execute();
+      $plans = mpull($plans, null, 'getPHID');
+    }
+
+    foreach ($page as $key => $build) {
+      $buildable_phid = $build->getBuildPlanPHID();
+      if (empty($plans[$buildable_phid])) {
+        unset($page[$key]);
+        continue;
+      }
+      $build->attachBuildPlan($plans[$buildable_phid]);
+    }
+
+    return $page;
+  }
+
   public function getQueryApplicationClass() {
     return 'PhabricatorApplicationHarbormaster';
   }
Index: src/applications/harbormaster/step/BuildStepImplementation.php
===================================================================
--- /dev/null
+++ src/applications/harbormaster/step/BuildStepImplementation.php
@@ -0,0 +1,48 @@
+<?php
+
+abstract class BuildStepImplementation {
+
+  private $settings;
+
+  /**
+   * The name of the implementation.
+   */
+  abstract public function getName();
+
+  /**
+   * The description of the implementation.
+   */
+  public function getDescription() {
+    return '';
+  }
+
+  /**
+   * Run the build step against the specified build.
+   */
+  abstract public function execute(HarbormasterBuild $build);
+
+  /**
+   * Gets the settings for this build step.
+   */
+  protected function getSettings() {
+    return $this->settings;
+  }
+
+  /**
+   * Loads the settings for this build step implementation from the build step.
+   */
+  public final function loadSettings(HarbormasterBuildStep $build_step) {
+    $this->settings = array();
+    foreach ($this->getSettingDefinitions() as $name => $opt) {
+      $this->settings[$name] = $build_step->getDetail($name);
+    }
+    return $this->settings;
+  }
+
+  /**
+   * Return an array of settings for this step implementation.
+   */
+  public function getSettingDefinitions() {
+    return array();
+  }
+}
Index: src/applications/harbormaster/step/SleepBuildStepImplementation.php
===================================================================
--- /dev/null
+++ src/applications/harbormaster/step/SleepBuildStepImplementation.php
@@ -0,0 +1,24 @@
+<?php
+
+final class SleepBuildStepImplementation extends BuildStepImplementation {
+
+  public function getName() {
+    return pht('Sleep');
+  }
+
+  public function getDescription() {
+    return pht('Sleep for a specified number of seconds.');
+  }
+
+  public function execute(HarbormasterBuild $build) {
+    $settings = $this->getSettings();
+
+    sleep($settings['seconds']);
+  }
+
+  public function getSettingDefinitions() {
+    return array(
+      'seconds' => array());
+  }
+
+}
Index: src/applications/harbormaster/storage/configuration/HarbormasterBuildStep.php
===================================================================
--- src/applications/harbormaster/storage/configuration/HarbormasterBuildStep.php
+++ src/applications/harbormaster/storage/configuration/HarbormasterBuildStep.php
@@ -1,14 +1,20 @@
 <?php
 
-final class HarbormasterBuildStep extends HarbormasterDAO {
+final class HarbormasterBuildStep extends HarbormasterDAO
+  implements PhabricatorPolicyInterface {
 
   protected $buildPlanPHID;
+  protected $className;
+  protected $details = array();
 
   private $buildPlan = self::ATTACHABLE;
 
   public function getConfiguration() {
     return array(
       self::CONFIG_AUX_PHID => true,
+      self::CONFIG_SERIALIZATION => array(
+        'details' => self::SERIALIZATION_JSON,
+      )
     ) + parent::getConfiguration();
   }
 
@@ -26,4 +32,47 @@
     return $this->assertAttached($this->buildPlan);
   }
 
+  public function getDetail($key, $default = null) {
+    return idx($this->details, $key, $default);
+  }
+
+  public function setDetail($key, $value) {
+    $this->details[$key] = $value;
+    return $this;
+  }
+
+  public function getStepImplementation() {
+    if ($this->className === null) {
+      throw new Exception("No implementation set for the given step.");
+    }
+
+    // TODO: We should look up the class in phutil's system to ensure
+    // that it actually extends BuildStepImplementation.
+    $class = $this->className;
+    $implementation = newv($class, array());
+    $implementation->loadSettings($this);
+    return $implementation;
+  }
+
+
+/* -(  PhabricatorPolicyInterface  )----------------------------------------- */
+
+
+  public function getCapabilities() {
+    return array(
+      PhabricatorPolicyCapability::CAN_VIEW,
+    );
+  }
+
+  public function getPolicy($capability) {
+    return $this->getBuildPlan()->getPolicy($capability);
+  }
+
+  public function hasAutomaticCapability($capability, PhabricatorUser $viewer) {
+    return $this->getBuildPlan()->hasAutomaticCapability($capability, $viewer);
+  }
+
+  public function describeAutomaticCapability($capability) {
+    return pht('A build step has the same policies as its build plan.');
+  }
 }
Index: src/applications/harbormaster/worker/HarbormasterBuildWorker.php
===================================================================
--- src/applications/harbormaster/worker/HarbormasterBuildWorker.php
+++ src/applications/harbormaster/worker/HarbormasterBuildWorker.php
@@ -32,11 +32,25 @@
       $buildable = $build->getBuildable();
       $plan = $build->getBuildPlan();
 
-      // TODO: Do the actual build here.
-      sleep(15);
+      $steps = id(new HarbormasterBuildStepQuery())
+        ->setViewer(PhabricatorUser::getOmnipotentUser())
+        ->withBuildPlanPHIDs(array($plan->getPHID()))
+        ->execute();
 
-      // If we get to here, then the build has passed.
-      $build->setBuildStatus(HarbormasterBuild::STATUS_PASSED);
+      // Perform the build.
+      foreach ($steps as $step) {
+        $implementation = $step->getStepImplementation();
+        $implementation->execute($build);
+        if ($build->getBuildStatus() !== HarbormasterBuild::STATUS_BUILDING) {
+          break;
+        }
+      }
+
+      // If we get to here, then the build has finished.  Set it to passed
+      // if no build step explicitly set the status.
+      if ($build->getBuildStatus() === HarbormasterBuild::STATUS_BUILDING) {
+        $build->setBuildStatus(HarbormasterBuild::STATUS_PASSED);
+      }
       $build->save();
     } catch (Exception $e) {
       // If any exception is raised, the build is marked as a failure and
Index: src/infrastructure/storage/patch/PhabricatorBuiltinPatchList.php
===================================================================
--- src/infrastructure/storage/patch/PhabricatorBuiltinPatchList.php
+++ src/infrastructure/storage/patch/PhabricatorBuiltinPatchList.php
@@ -1720,6 +1720,10 @@
         'type' => 'sql',
         'name' => $this->getPatchPath('20131031.vcspassword.sql'),
       ),
+      '20131105.buildstep.sql' => array(
+        'type' => 'sql',
+        'name' => $this->getPatchPath('20131105.buildstep.sql'),
+      ),
     );
   }
 }