Index: src/__phutil_library_map__.php
===================================================================
--- src/__phutil_library_map__.php
+++ src/__phutil_library_map__.php
@@ -26,6 +26,7 @@
     'ArcanistBranchWorkflow' => 'workflow/ArcanistBranchWorkflow.php',
     'ArcanistBritishTestCase' => 'configuration/__tests__/ArcanistBritishTestCase.php',
     'ArcanistBrowseWorkflow' => 'workflow/ArcanistBrowseWorkflow.php',
+    'ArcanistBuildAgentWorkflow' => 'workflow/ArcanistBuildAgentWorkflow.php',
     'ArcanistBundle' => 'parser/ArcanistBundle.php',
     'ArcanistBundleTestCase' => 'parser/__tests__/ArcanistBundleTestCase.php',
     'ArcanistCSSLintLinter' => 'lint/linter/ArcanistCSSLintLinter.php',
@@ -167,6 +168,7 @@
     'ArcanistXHPASTLinter' => 'lint/linter/ArcanistXHPASTLinter.php',
     'ArcanistXHPASTLinterTestCase' => 'lint/linter/__tests__/ArcanistXHPASTLinterTestCase.php',
     'ArcanistXUnitTestResultParser' => 'unit/engine/ArcanistXUnitTestResultParser.php',
+    'BuildStepImplementation' => 'build/BuildStepImplementation.php',
     'CSharpToolsTestEngine' => 'unit/engine/CSharpToolsTestEngine.php',
     'ComprehensiveLintEngine' => 'lint/engine/ComprehensiveLintEngine.php',
     'ExampleLintEngine' => 'lint/engine/ExampleLintEngine.php',
@@ -180,6 +182,7 @@
     'PhutilUnitTestEngine' => 'unit/engine/PhutilUnitTestEngine.php',
     'PhutilUnitTestEngineTestCase' => 'unit/engine/__tests__/PhutilUnitTestEngineTestCase.php',
     'PytestTestEngine' => 'unit/engine/PytestTestEngine.php',
+    'SleepBuildStepImplementation' => 'build/SleepBuildStepImplementation.php',
     'UnitTestableArcanistLintEngine' => 'lint/engine/UnitTestableArcanistLintEngine.php',
     'XUnitTestEngine' => 'unit/engine/XUnitTestEngine.php',
     'XUnitTestResultParserTestCase' => 'unit/engine/__tests__/XUnitTestResultParserTestCase.php',
@@ -202,6 +205,7 @@
     'ArcanistBranchWorkflow' => 'ArcanistFeatureWorkflow',
     'ArcanistBritishTestCase' => 'ArcanistTestCase',
     'ArcanistBrowseWorkflow' => 'ArcanistBaseWorkflow',
+    'ArcanistBuildAgentWorkflow' => 'ArcanistBaseWorkflow',
     'ArcanistBundleTestCase' => 'ArcanistTestCase',
     'ArcanistCSSLintLinter' => 'ArcanistExternalLinter',
     'ArcanistCSSLintLinterTestCase' => 'ArcanistArcanistLinterTestCase',
@@ -323,6 +327,7 @@
     'PhutilUnitTestEngine' => 'ArcanistBaseUnitTestEngine',
     'PhutilUnitTestEngineTestCase' => 'ArcanistTestCase',
     'PytestTestEngine' => 'ArcanistBaseUnitTestEngine',
+    'SleepBuildStepImplementation' => 'BuildStepImplementation',
     'UnitTestableArcanistLintEngine' => 'ArcanistLintEngine',
     'XUnitTestEngine' => 'ArcanistBaseUnitTestEngine',
     'XUnitTestResultParserTestCase' => 'ArcanistTestCase',
Index: src/build/BuildStepImplementation.php
===================================================================
--- /dev/null
+++ src/build/BuildStepImplementation.php
@@ -0,0 +1,88 @@
+<?php
+
+abstract class BuildStepImplementation {
+
+  private $settings;
+
+  const SETTING_TYPE_STRING = 'string';
+  const SETTING_TYPE_INTEGER = 'integer';
+  const SETTING_TYPE_BOOLEAN = 'boolean';
+
+  public static function getImplementations() {
+    $symbols = id(new PhutilSymbolLoader())
+      ->setAncestorClass("BuildStepImplementation")
+      ->setConcreteOnly(true)
+      ->selectAndLoadSymbols();
+    return ipull($symbols, 'name');
+  }
+
+  /**
+   * The name of the implementation.
+   */
+  abstract public function getName();
+
+  /**
+   * The generic description of the implementation.
+   */
+  public function getGenericDescription() {
+    return '';
+  }
+
+  /**
+   * The description of the implementation, based on the current settings.
+   */
+  public function getDescription() {
+    return '';
+  }
+
+  /**
+   * Run the build step against the specified build.
+   */
+  abstract public function execute(RemoteHarbormasterBuild $build);
+
+  /**
+   * Gets the settings for this build step.
+   */
+  public function getSettings() {
+    return $this->settings;
+  }
+
+  /**
+   * Validate the current settings of this build step.
+   */
+  public function validate() {
+    return true;
+  }
+
+  /**
+   * Loads the settings for this build step implementation from the build step.
+   */
+  public final function loadSettings(array $details) {
+    $this->settings = array();
+    $this->validateSettingDefinitions();
+    foreach ($this->getSettingDefinitions() as $name => $opt) {
+      $this->settings[$name] = idx($details, $name, null);
+    }
+    return $this->settings;
+  }
+
+  /**
+   * Validates that the setting definitions for this implementation are valid.
+   */
+  public final function validateSettingDefinitions() {
+    foreach ($this->getSettingDefinitions() as $name => $opt) {
+      if (!isset($opt['type'])) {
+        throw new Exception(
+          'Setting definition \''.$name.
+          '\' is missing type requirement.');
+      }
+    }
+  }
+
+  /**
+   * Return an array of settings for this step implementation.
+   */
+  public function getSettingDefinitions() {
+    return array();
+  }
+}
Index: src/build/RemoteHarbormasterBuild.php
===================================================================
--- /dev/null
+++ src/build/RemoteHarbormasterBuild.php
@@ -0,0 +1,5 @@
+<?php
+
+final class RemoteHarbormasterBuild {
+
+}
Index: src/build/SleepBuildStepImplementation.php
===================================================================
--- /dev/null
+++ src/build/SleepBuildStepImplementation.php
@@ -0,0 +1,45 @@
+<?php
+
+final class SleepBuildStepImplementation extends BuildStepImplementation {
+
+  public function getName() {
+    return pht('Sleep');
+  }
+
+  public function getGenericDescription() {
+    return pht('Sleep for a specified number of seconds.');
+  }
+
+  public function getDescription() {
+    $settings = $this->getSettings();
+
+    return pht('Sleep for %s seconds.', $settings['seconds']);
+  }
+
+  public function execute(RemoteHarbormasterBuild $build) {
+    $settings = $this->getSettings();
+
+    sleep($settings['seconds']);
+  }
+
+  public function validateSettings() {
+    $settings = $this->getSettings();
+
+    if ($settings['seconds'] === null) {
+      return false;
+    }
+    if (!is_int($settings['seconds'])) {
+      return false;
+    }
+    return true;
+  }
+
+  public function getSettingDefinitions() {
+    return array(
+      'seconds' => array(
+        'name' => 'Seconds',
+        'description' => 'The number of seconds to sleep for.',
+        'type' => BuildStepImplementation::SETTING_TYPE_INTEGER));
+  }
+
+}
Index: src/workflow/ArcanistBuildAgentWorkflow.php
===================================================================
--- /dev/null
+++ src/workflow/ArcanistBuildAgentWorkflow.php
@@ -0,0 +1,75 @@
+<?php
+/**
+ * Runs a harbormaster build agent on the local machine
+ * @group workflow
+ */
+
+final class ArcanistBuildAgentWorkflow extends ArcanistBaseWorkflow {
+
+  public function getWorkflowName() {
+    return 'agent';
+  }
+
+  public function requiresConduit() {
+    return true;
+  }
+
+  public function requiresAuthentication() {
+    return true;
+  }
+
+  public function getCommandSynopses() {
+    return phutil_console_format(<<<EOTEXT
+      **agent** [__options__]
+EOTEXT
+    );
+  }
+
+  public function getCommandHelp() {
+    return phutil_console_format(<<<EOTEXT
+          Supports: http, https
+          Runs a Harbormaster agent on the current machine.  You must
+          explicitly provide the Conduit URI for this command.
+EOTEXT
+    );
+  }
+
+  public function getArguments() {
+    return array(
+      'category' => array(
+        'short' => 'c',
+        'param' => 'category',
+        'help'  => "Specify the category of the build agent.",
+      )
+    );
+  }
+
+  public function run() {
+    $console = PhutilConsole::getConsole();
+    $console->writeOut("Starting build agent...\n");
+
+    // Pool for agent instructions.
+    $conduit = $this->getConduit();
+    while (true) {
+      $item = $conduit->callMethodSynchronous('agent.nextbuild', array());
+      if ($item["exists"]) {
+        $steps = $item["steps"];
+
+        // $steps is an array like so:
+        // array(
+        //   array(
+        //     "class" => "SleepBuildStepImplementation",
+        //     "details" => "{\"seconds\":5}"),
+        //   array(
+        //     "class" => "SleepBuildStepImplementation",
+        //     "details" => "{\"seconds\":15}"))
+        // TODO: Do something with this.
+      } else {
+        $console->writeOut("> No build to pick up. \n");
+        sleep(15);
+      }
+    }
+
+  }
+}
+