diff --git a/src/applications/diffusion/conduit/DiffusionBranchQueryConduitAPIMethod.php b/src/applications/diffusion/conduit/DiffusionBranchQueryConduitAPIMethod.php
--- a/src/applications/diffusion/conduit/DiffusionBranchQueryConduitAPIMethod.php
+++ b/src/applications/diffusion/conduit/DiffusionBranchQueryConduitAPIMethod.php
@@ -56,7 +56,10 @@
     } else {
       $refs = id(new DiffusionLowLevelGitRefQuery())
         ->setRepository($repository)
-        ->withIsOriginBranch(true)
+        ->withRefTypes(
+          array(
+            PhabricatorRepositoryRefCursor::TYPE_BRANCH,
+          ))
         ->execute();
     }
 
diff --git a/src/applications/diffusion/conduit/DiffusionTagsQueryConduitAPIMethod.php b/src/applications/diffusion/conduit/DiffusionTagsQueryConduitAPIMethod.php
--- a/src/applications/diffusion/conduit/DiffusionTagsQueryConduitAPIMethod.php
+++ b/src/applications/diffusion/conduit/DiffusionTagsQueryConduitAPIMethod.php
@@ -72,7 +72,10 @@
 
     $refs = id(new DiffusionLowLevelGitRefQuery())
       ->setRepository($repository)
-      ->withIsTag(true)
+      ->withRefTypes(
+        array(
+          PhabricatorRepositoryRefCursor::TYPE_TAG,
+        ))
       ->execute();
 
     $tags = array();
diff --git a/src/applications/diffusion/editor/DiffusionURIEditor.php b/src/applications/diffusion/editor/DiffusionURIEditor.php
--- a/src/applications/diffusion/editor/DiffusionURIEditor.php
+++ b/src/applications/diffusion/editor/DiffusionURIEditor.php
@@ -463,6 +463,8 @@
       break;
     }
 
+    $was_hosted = $repository->isHosted();
+
     if ($observe_uri) {
       $repository
         ->setHosted(false)
@@ -477,6 +479,17 @@
 
     $repository->save();
 
+    $is_hosted = $repository->isHosted();
+
+    // If we've swapped the repository from hosted to observed or vice versa,
+    // reset all the cluster version clocks.
+    if ($was_hosted != $is_hosted) {
+      $cluster_engine = id(new DiffusionRepositoryClusterEngine())
+        ->setViewer($this->getActor())
+        ->setRepository($repository)
+        ->synchronizeWorkingCopyAfterHostingChange();
+    }
+
     return $xactions;
   }
 
diff --git a/src/applications/diffusion/management/DiffusionRepositoryStorageManagementPanel.php b/src/applications/diffusion/management/DiffusionRepositoryStorageManagementPanel.php
--- a/src/applications/diffusion/management/DiffusionRepositoryStorageManagementPanel.php
+++ b/src/applications/diffusion/management/DiffusionRepositoryStorageManagementPanel.php
@@ -137,12 +137,28 @@
         $version = idx($versions, $device->getPHID());
         if ($version) {
           $version_number = $version->getRepositoryVersion();
-          $version_number = phutil_tag(
-            'a',
-            array(
-              'href' => "/diffusion/pushlog/view/{$version_number}/",
-            ),
-            $version_number);
+
+          $href = null;
+          if ($repository->isHosted()) {
+            $href = "/diffusion/pushlog/view/{$version_number}/";
+          } else {
+            $commit = id(new DiffusionCommitQuery())
+              ->setViewer($viewer)
+              ->withIDs(array($version_number))
+              ->executeOne();
+            if ($commit) {
+              $href = $commit->getURI();
+            }
+          }
+
+          if ($href) {
+            $version_number = phutil_tag(
+              'a',
+              array(
+                'href' => $href,
+              ),
+              $version_number);
+          }
         } else {
           $version_number = '-';
         }
diff --git a/src/applications/diffusion/protocol/DiffusionRepositoryClusterEngine.php b/src/applications/diffusion/protocol/DiffusionRepositoryClusterEngine.php
--- a/src/applications/diffusion/protocol/DiffusionRepositoryClusterEngine.php
+++ b/src/applications/diffusion/protocol/DiffusionRepositoryClusterEngine.php
@@ -85,6 +85,53 @@
   /**
    * @task sync
    */
+  public function synchronizeWorkingCopyAfterHostingChange() {
+    if (!$this->shouldEnableSynchronization()) {
+      return;
+    }
+
+    $repository = $this->getRepository();
+    $repository_phid = $repository->getPHID();
+
+    $versions = PhabricatorRepositoryWorkingCopyVersion::loadVersions(
+      $repository_phid);
+    $versions = mpull($versions, null, 'getDevicePHID');
+
+    // After converting a hosted repository to observed, or vice versa, we
+    // need to reset version numbers because the clocks for observed and hosted
+    // repositories run on different units.
+
+    // We identify all the cluster leaders and reset their version to 0.
+    // We identify all the cluster followers and demote them.
+
+    // This allows the cluter to start over again at version 0 but keep the
+    // same leaders.
+
+    if ($versions) {
+      $max_version = (int)max(mpull($versions, 'getRepositoryVersion'));
+      foreach ($versions as $version) {
+        $device_phid = $version->getDevicePHID();
+
+        if ($version->getRepositoryVersion() == $max_version) {
+          PhabricatorRepositoryWorkingCopyVersion::updateVersion(
+            $repository_phid,
+            $device_phid,
+            0);
+        } else {
+          PhabricatorRepositoryWorkingCopyVersion::demoteDevice(
+            $repository_phid,
+            $device_phid);
+        }
+      }
+    }
+
+    return $this;
+  }
+
+
+  /**
+   * @task sync
+   */
   public function synchronizeWorkingCopyBeforeRead() {
     if (!$this->shouldEnableSynchronization()) {
       return;
@@ -149,14 +196,18 @@
 
       $max_version = (int)max(mpull($versions, 'getRepositoryVersion'));
       if ($max_version > $this_version) {
-        $fetchable = array();
-        foreach ($versions as $version) {
-          if ($version->getRepositoryVersion() == $max_version) {
-            $fetchable[] = $version->getDevicePHID();
+        if ($repository->isHosted()) {
+          $fetchable = array();
+          foreach ($versions as $version) {
+            if ($version->getRepositoryVersion() == $max_version) {
+              $fetchable[] = $version->getDevicePHID();
+            }
           }
-        }
 
-        $this->synchronizeWorkingCopyFromDevices($fetchable);
+          $this->synchronizeWorkingCopyFromDevices($fetchable);
+        } else {
+          $this->synchornizeWorkingCopyFromRemote();
+        }
 
         PhabricatorRepositoryWorkingCopyVersion::updateVersion(
           $repository_phid,
@@ -329,6 +380,47 @@
   }
 
 
+  public function synchronizeWorkingCopyAfterDiscovery($new_version) {
+    if (!$this->shouldEnableSynchronization()) {
+      return;
+    }
+
+    $repository = $this->getRepository();
+    $repository_phid = $repository->getPHID();
+    if ($repository->isHosted()) {
+      return;
+    }
+
+    $viewer = $this->getViewer();
+
+    $device = AlmanacKeys::getLiveDevice();
+    $device_phid = $device->getPHID();
+
+    // NOTE: We are not holding a lock here because this method is only called
+    // from PhabricatorRepositoryDiscoveryEngine, which already holds a device
+    // lock. Even if we do race here and record an older version, the
+    // consequences are mild: we only do extra work to correct it later.
+
+    $versions = PhabricatorRepositoryWorkingCopyVersion::loadVersions(
+      $repository_phid);
+    $versions = mpull($versions, null, 'getDevicePHID');
+
+    $this_version = idx($versions, $device_phid);
+    if ($this_version) {
+      $this_version = (int)$this_version->getRepositoryVersion();
+    } else {
+      $this_version = -1;
+    }
+
+    if ($new_version > $this_version) {
+      PhabricatorRepositoryWorkingCopyVersion::updateVersion(
+        $repository_phid,
+        $device_phid,
+        $new_version);
+    }
+  }
+
+
   /**
    * @task sync
    */
@@ -471,13 +563,6 @@
       return false;
     }
 
-    // TODO: It may eventually make sense to try to version and synchronize
-    // observed repositories (so that daemons don't do reads against out-of
-    // date hosts), but don't bother for now.
-    if (!$repository->isHosted()) {
-      return false;
-    }
-
     $device = AlmanacKeys::getLiveDevice();
     if (!$device) {
       return false;
@@ -490,6 +575,50 @@
   /**
    * @task internal
    */
+  private function synchornizeWorkingCopyFromRemote() {
+    $repository = $this->getRepository();
+    $device = AlmanacKeys::getLiveDevice();
+
+    $local_path = $repository->getLocalPath();
+    $fetch_uri = $repository->getRemoteURIEnvelope();
+
+    if ($repository->isGit()) {
+      $this->requireWorkingCopy();
+
+      $argv = array(
+        'fetch --prune -- %P %s',
+        $fetch_uri,
+        '+refs/*:refs/*',
+      );
+    } else {
+      throw new Exception(pht('Remote sync only supported for git!'));
+    }
+
+    $future = DiffusionCommandEngine::newCommandEngine($repository)
+      ->setArgv($argv)
+      ->setSudoAsDaemon(true)
+      ->setCredentialPHID($repository->getCredentialPHID())
+      ->setProtocol($repository->getRemoteProtocol())
+      ->newFuture();
+
+    $future->setCWD($local_path);
+
+    try {
+      $future->resolvex();
+    } catch (Exception $ex) {
+      $this->logLine(
+        pht(
+          'Synchronization of "%s" from remote failed: %s',
+          $device->getName(),
+          $ex->getMessage()));
+      throw $ex;
+    }
+  }
+
+
+  /**
+   * @task internal
+   */
   private function synchronizeWorkingCopyFromDevices(array $device_phids) {
     $repository = $this->getRepository();
 
@@ -560,17 +689,7 @@
     $local_path = $repository->getLocalPath();
 
     if ($repository->isGit()) {
-      if (!Filesystem::pathExists($local_path)) {
-        throw new Exception(
-          pht(
-            'Repository "%s" does not have a working copy on this device '.
-            'yet, so it can not be synchronized. Wait for the daemons to '.
-            'construct one or run `bin/repository update %s` on this host '.
-            '("%s") to build it explicitly.',
-            $repository->getDisplayName(),
-            $repository->getMonogram(),
-            $device->getName()));
-      }
+      $this->requireWorkingCopy();
 
       $argv = array(
         'fetch --prune -- %s %s',
@@ -622,4 +741,24 @@
     }
     return $this;
   }
+
+  private function requireWorkingCopy() {
+    $repository = $this->getRepository();
+    $local_path = $repository->getLocalPath();
+
+    if (!Filesystem::pathExists($local_path)) {
+      $device = AlmanacKeys::getLiveDevice();
+
+      throw new Exception(
+        pht(
+          'Repository "%s" does not have a working copy on this device '.
+          'yet, so it can not be synchronized. Wait for the daemons to '.
+          'construct one or run `bin/repository update %s` on this host '.
+          '("%s") to build it explicitly.',
+          $repository->getDisplayName(),
+          $repository->getMonogram(),
+          $device->getName()));
+    }
+  }
+
 }
diff --git a/src/applications/diffusion/query/lowlevel/DiffusionLowLevelGitRefQuery.php b/src/applications/diffusion/query/lowlevel/DiffusionLowLevelGitRefQuery.php
--- a/src/applications/diffusion/query/lowlevel/DiffusionLowLevelGitRefQuery.php
+++ b/src/applications/diffusion/query/lowlevel/DiffusionLowLevelGitRefQuery.php
@@ -6,30 +6,33 @@
  */
 final class DiffusionLowLevelGitRefQuery extends DiffusionLowLevelQuery {
 
-  private $isTag;
-  private $isOriginBranch;
+  private $refTypes;
 
-  public function withIsTag($is_tag) {
-    $this->isTag = $is_tag;
-    return $this;
-  }
-
-  public function withIsOriginBranch($is_origin_branch) {
-    $this->isOriginBranch = $is_origin_branch;
+  public function withRefTypes(array $ref_types) {
+    $this->refTypes = $ref_types;
     return $this;
   }
 
   protected function executeQuery() {
+    $ref_types = $this->refTypes;
+    if ($ref_types) {
+      $type_branch = PhabricatorRepositoryRefCursor::TYPE_BRANCH;
+      $type_tag = PhabricatorRepositoryRefCursor::TYPE_TAG;
+
+      $ref_types = array_fuse($ref_types);
+
+      $with_branches = isset($ref_types[$type_branch]);
+      $with_tags = isset($ref_types[$type_tag]);
+    } else {
+      $with_branches = true;
+      $with_tags = true;
+    }
+
     $repository = $this->getRepository();
 
     $prefixes = array();
 
-    $any = ($this->isTag || $this->isOriginBranch);
-    if (!$any) {
-      throw new Exception(pht('Specify types of refs to query.'));
-    }
-
-    if ($this->isOriginBranch) {
+    if ($with_branches) {
       if ($repository->isWorkingCopyBare()) {
         $prefix = 'refs/heads/';
       } else {
@@ -39,7 +42,7 @@
       $prefixes[] = $prefix;
     }
 
-    if ($this->isTag) {
+    if ($with_tags) {
       $prefixes[] = 'refs/tags/';
     }
 
diff --git a/src/applications/diffusion/query/lowlevel/DiffusionLowLevelResolveRefsQuery.php b/src/applications/diffusion/query/lowlevel/DiffusionLowLevelResolveRefsQuery.php
--- a/src/applications/diffusion/query/lowlevel/DiffusionLowLevelResolveRefsQuery.php
+++ b/src/applications/diffusion/query/lowlevel/DiffusionLowLevelResolveRefsQuery.php
@@ -66,8 +66,11 @@
     // First, resolve branches and tags.
     $ref_map = id(new DiffusionLowLevelGitRefQuery())
       ->setRepository($repository)
-      ->withIsTag(true)
-      ->withIsOriginBranch(true)
+      ->withRefTypes(
+        array(
+          PhabricatorRepositoryRefCursor::TYPE_BRANCH,
+          PhabricatorRepositoryRefCursor::TYPE_TAG,
+        ))
       ->execute();
     $ref_map = mgroup($ref_map, 'getShortName');
 
diff --git a/src/applications/repository/engine/PhabricatorRepositoryDiscoveryEngine.php b/src/applications/repository/engine/PhabricatorRepositoryDiscoveryEngine.php
--- a/src/applications/repository/engine/PhabricatorRepositoryDiscoveryEngine.php
+++ b/src/applications/repository/engine/PhabricatorRepositoryDiscoveryEngine.php
@@ -63,6 +63,7 @@
 
   private function discoverCommitsWithLock() {
     $repository = $this->getRepository();
+    $viewer = $this->getViewer();
 
     $vcs = $repository->getVersionControlSystem();
     switch ($vcs) {
@@ -104,6 +105,14 @@
       $this->commitCache[$ref->getIdentifier()] = true;
     }
 
+    $version = $this->getObservedVersion($repository);
+    if ($version !== null) {
+      id(new DiffusionRepositoryClusterEngine())
+        ->setViewer($viewer)
+        ->setRepository($repository)
+        ->synchronizeWorkingCopyAfterDiscovery($version);
+    }
+
     return $refs;
   }
 
@@ -121,9 +130,15 @@
       $this->verifyGitOrigin($repository);
     }
 
+    // TODO: This should also import tags, but some of the logic is still
+    // branch-specific today.
+
     $branches = id(new DiffusionLowLevelGitRefQuery())
       ->setRepository($repository)
-      ->withIsOriginBranch(true)
+      ->withRefTypes(
+        array(
+          PhabricatorRepositoryRefCursor::TYPE_BRANCH,
+        ))
       ->execute();
 
     if (!$branches) {
@@ -642,4 +657,49 @@
     return true;
   }
 
+
+  private function getObservedVersion(PhabricatorRepository $repository) {
+    if ($repository->isHosted()) {
+      return null;
+    }
+
+    if ($repository->isGit()) {
+      return $this->getGitObservedVersion($repository);
+    }
+
+    return null;
+  }
+
+  private function getGitObservedVersion(PhabricatorRepository $repository) {
+    $refs = id(new DiffusionLowLevelGitRefQuery())
+     ->setRepository($repository)
+     ->execute();
+    if (!$refs) {
+      return null;
+    }
+
+    // In Git, the observed version is the most recently discovered commit
+    // at any repository HEAD. It's possible for this to regress temporarily
+    // if a branch is pushed and then deleted. This is acceptable because it
+    // doesn't do anything meaningfully bad and will fix itself on the next
+    // push.
+
+    $ref_identifiers = mpull($refs, 'getCommitIdentifier');
+    $ref_identifiers = array_fuse($ref_identifiers);
+
+    $version = queryfx_one(
+      $repository->establishConnection('w'),
+      'SELECT MAX(id) version FROM %T WHERE repositoryID = %d
+        AND commitIdentifier IN (%Ls)',
+      id(new PhabricatorRepositoryCommit())->getTableName(),
+      $repository->getID(),
+      $ref_identifiers);
+
+    if (!$version) {
+      return null;
+    }
+
+    return (int)$version['version'];
+  }
+
 }
diff --git a/src/applications/repository/engine/PhabricatorRepositoryPullEngine.php b/src/applications/repository/engine/PhabricatorRepositoryPullEngine.php
--- a/src/applications/repository/engine/PhabricatorRepositoryPullEngine.php
+++ b/src/applications/repository/engine/PhabricatorRepositoryPullEngine.php
@@ -108,27 +108,27 @@
         } else {
           $this->executeSubversionCreate();
         }
-      } else {
-        if (!$repository->isHosted()) {
-          $this->logPull(
-            pht(
-              'Updating the working copy for repository "%s".',
-              $repository->getDisplayName()));
-          if ($is_git) {
-            $this->verifyGitOrigin($repository);
-            $this->executeGitUpdate();
-          } else if ($is_hg) {
-            $this->executeMercurialUpdate();
-          }
+      }
+
+      id(new DiffusionRepositoryClusterEngine())
+        ->setViewer($viewer)
+        ->setRepository($repository)
+        ->synchronizeWorkingCopyBeforeRead();
+
+      if (!$repository->isHosted()) {
+        $this->logPull(
+          pht(
+            'Updating the working copy for repository "%s".',
+            $repository->getDisplayName()));
+        if ($is_git) {
+          $this->verifyGitOrigin($repository);
+          $this->executeGitUpdate();
+        } else if ($is_hg) {
+          $this->executeMercurialUpdate();
         }
       }
 
       if ($repository->isHosted()) {
-        id(new DiffusionRepositoryClusterEngine())
-          ->setViewer($viewer)
-          ->setRepository($repository)
-          ->synchronizeWorkingCopyBeforeRead();
-
         if ($is_git) {
           $this->installGitHook();
         } else if ($is_svn) {
diff --git a/src/applications/repository/engine/PhabricatorRepositoryRefEngine.php b/src/applications/repository/engine/PhabricatorRepositoryRefEngine.php
--- a/src/applications/repository/engine/PhabricatorRepositoryRefEngine.php
+++ b/src/applications/repository/engine/PhabricatorRepositoryRefEngine.php
@@ -452,7 +452,10 @@
   private function loadGitBranchPositions(PhabricatorRepository $repository) {
     return id(new DiffusionLowLevelGitRefQuery())
       ->setRepository($repository)
-      ->withIsOriginBranch(true)
+      ->withRefTypes(
+        array(
+          PhabricatorRepositoryRefCursor::TYPE_BRANCH,
+        ))
       ->execute();
   }
 
@@ -463,7 +466,10 @@
   private function loadGitTagPositions(PhabricatorRepository $repository) {
     return id(new DiffusionLowLevelGitRefQuery())
       ->setRepository($repository)
-      ->withIsTag(true)
+      ->withRefTypes(
+        array(
+          PhabricatorRepositoryRefCursor::TYPE_TAG,
+        ))
       ->execute();
   }