Index: src/__phutil_library_map__.php
===================================================================
--- src/__phutil_library_map__.php
+++ src/__phutil_library_map__.php
@@ -2282,6 +2282,7 @@
     'PonderVoteSaveController' => 'applications/ponder/controller/PonderVoteSaveController.php',
     'ProjectCapabilityCreateProjects' => 'applications/project/capability/ProjectCapabilityCreateProjects.php',
     'ProjectRemarkupRule' => 'applications/project/remarkup/ProjectRemarkupRule.php',
+    'PublishFragmentBuildStepImplementation' => 'applications/harbormaster/step/PublishFragmentBuildStepImplementation.php',
     'QueryFormattingTestCase' => 'infrastructure/storage/__tests__/QueryFormattingTestCase.php',
     'ReleephAuthorFieldSpecification' => 'applications/releeph/field/specification/ReleephAuthorFieldSpecification.php',
     'ReleephBranch' => 'applications/releeph/storage/ReleephBranch.php',
@@ -4947,6 +4948,7 @@
     'PonderVoteSaveController' => 'PonderController',
     'ProjectCapabilityCreateProjects' => 'PhabricatorPolicyCapability',
     'ProjectRemarkupRule' => 'PhabricatorRemarkupRuleObject',
+    'PublishFragmentBuildStepImplementation' => 'VariableBuildStepImplementation',
     'QueryFormattingTestCase' => 'PhabricatorTestCase',
     'ReleephAuthorFieldSpecification' => 'ReleephFieldSpecification',
     'ReleephBranch' =>
Index: src/applications/harbormaster/step/LeaseHostBuildStepImplementation.php
===================================================================
--- src/applications/harbormaster/step/LeaseHostBuildStepImplementation.php
+++ src/applications/harbormaster/step/LeaseHostBuildStepImplementation.php
@@ -53,7 +53,7 @@
     $settings = $this->getSettings();
 
     return array(
-      $settings['name'] => 'host');
+      $settings['name'] => HarbormasterBuildArtifact::TYPE_HOST);
   }
 
   public function validateSettings() {
Index: src/applications/harbormaster/step/PublishFragmentBuildStepImplementation.php
===================================================================
--- /dev/null
+++ src/applications/harbormaster/step/PublishFragmentBuildStepImplementation.php
@@ -0,0 +1,91 @@
+<?php
+
+final class PublishFragmentBuildStepImplementation
+  extends VariableBuildStepImplementation {
+
+  public function getName() {
+    return pht('Publish Fragment');
+  }
+
+  public function getGenericDescription() {
+    return pht('Publish a fragment based on a file artifact.');
+  }
+
+  public function getDescription() {
+    $settings = $this->getSettings();
+
+    return pht(
+      'Publish file artifact \'%s\' to the fragment path \'%s\'.',
+      $settings['artifact'],
+      $settings['path']);
+  }
+
+  public function execute(
+    HarbormasterBuild $build,
+    HarbormasterBuildTarget $build_target) {
+
+    $settings = $this->getSettings();
+    $variables = $build_target->getVariables();
+
+    $path = $this->mergeVariables(
+      'vsprintf',
+      $settings['path'],
+      $variables);
+
+    $artifact = $build->loadArtifact($settings['artifact']);
+
+    $file = $artifact->loadPhabricatorFile();
+
+    $fragment = id(new PhragmentFragmentQuery())
+      ->setViewer(PhabricatorUser::getOmnipotentUser())
+      ->withPaths(array($path))
+      ->executeOne();
+
+    if ($fragment === null) {
+      PhragmentFragment::createFromFile(
+        PhabricatorUser::getOmnipotentUser(),
+        $file,
+        $path,
+        PhabricatorPolicies::getMostOpenPolicy(),
+        PhabricatorPolicies::POLICY_USER);
+    } else {
+      if ($file->getMimeType() === "application/zip") {
+        $fragment->updateFromZIP(PhabricatorUser::getOmnipotentUser(), $file);
+      } else {
+        $fragment->updateFromFile(PhabricatorUser::getOmnipotentUser(), $file);
+      }
+    }
+  }
+
+  public function validateSettings() {
+    $settings = $this->getSettings();
+
+    if ($settings['path'] === null || !is_string($settings['path'])) {
+      return false;
+    }
+    if ($settings['artifact'] === null ||
+      !is_string($settings['artifact'])) {
+      return false;
+    }
+
+    // TODO: Check if the file artifact is provided by previous build steps.
+
+    return true;
+  }
+
+  public function getSettingDefinitions() {
+    return array(
+      'path' => array(
+        'name' => 'Path',
+        'description' =>
+          'The path of the fragment that will be published.',
+        'type' => BuildStepImplementation::SETTING_TYPE_STRING),
+      'artifact' => array(
+        'name' => 'File Artifact',
+        'description' =>
+          'The file artifact that will be published to Phragment.',
+        'type' => BuildStepImplementation::SETTING_TYPE_ARTIFACT,
+        'artifact_type' => HarbormasterBuildArtifact::TYPE_FILE));
+  }
+
+}
Index: src/applications/harbormaster/step/UploadArtifactBuildStepImplementation.php
===================================================================
--- src/applications/harbormaster/step/UploadArtifactBuildStepImplementation.php
+++ src/applications/harbormaster/step/UploadArtifactBuildStepImplementation.php
@@ -51,6 +51,13 @@
     $artifact->save();
   }
 
+  public function getArtifactMappings() {
+    $settings = $this->getSettings();
+
+    return array(
+      $settings['name'] => HarbormasterBuildArtifact::TYPE_FILE);
+  }
+
   public function validateSettings() {
     $settings = $this->getSettings();
 
Index: src/applications/harbormaster/storage/build/HarbormasterBuildArtifact.php
===================================================================
--- src/applications/harbormaster/storage/build/HarbormasterBuildArtifact.php
+++ src/applications/harbormaster/storage/build/HarbormasterBuildArtifact.php
@@ -96,6 +96,28 @@
     return $lease;
   }
 
+  public function loadPhabricatorFile() {
+    if ($this->getArtifactType() !== self::TYPE_FILE) {
+      throw new Exception(
+        "`loadPhabricatorFile` may only be called on file artifacts.");
+    }
+
+    $data = $this->getArtifactData();
+
+    // The data for TYPE_FILE is an array with a single PHID in it.
+    $phid = $data["filePHID"];
+
+    $file = id(new PhabricatorFileQuery())
+      ->setViewer(PhabricatorUser::getOmnipotentUser())
+      ->withPHIDs(array($phid))
+      ->executeOne();
+    if ($file === null) {
+      throw new Exception("Associated file not found!");
+    }
+    return $file;
+  }
+
+
 /* -(  PhabricatorPolicyInterface  )----------------------------------------- */