diff --git a/config/config.exs b/config/config.exs
index 7ea3353..fe9e944 100644
--- a/config/config.exs
+++ b/config/config.exs
@@ -10,7 +10,8 @@ config :parrhesia,
     private_key: nil
   ],
   sync: [
-    path: nil
+    path: nil,
+    start_workers?: true
   ],
   limits: [
     max_frame_bytes: 1_048_576,
diff --git a/config/runtime.exs b/config/runtime.exs
index b0aa688..462981e 100644
--- a/config/runtime.exs
+++ b/config/runtime.exs
@@ -456,7 +456,12 @@ if config_env() == :prod do
       private_key: string_env.("PARRHESIA_IDENTITY_PRIVATE_KEY", nil)
     ],
     sync: [
-      path: string_env.("PARRHESIA_SYNC_PATH", nil)
+      path: string_env.("PARRHESIA_SYNC_PATH", nil),
+      start_workers?:
+        bool_env.(
+          "PARRHESIA_SYNC_START_WORKERS",
+          Keyword.get(Application.get_env(:parrhesia, :sync, []), :start_workers?, true)
+        )
     ],
     moderation_cache_enabled:
       bool_env.("PARRHESIA_MODERATION_CACHE_ENABLED", moderation_cache_enabled_default),
diff --git a/config/test.exs b/config/test.exs
index 0c585cb..235eed7 100644
--- a/config/test.exs
+++ b/config/test.exs
@@ -20,7 +20,8 @@ config :parrhesia,
     private_key: nil
   ],
   sync: [
-    path: Path.join(System.tmp_dir!(), "parrhesia_test_sync.json")
+    path: Path.join(System.tmp_dir!(), "parrhesia_test_sync.json"),
+    start_workers?: false
   ],
   features: [verify_event_signatures: false]
 
diff --git a/lib/parrhesia/api/sync/manager.ex b/lib/parrhesia/api/sync/manager.ex
index 48ba7f0..0b60957 100644
--- a/lib/parrhesia/api/sync/manager.ex
+++ b/lib/parrhesia/api/sync/manager.ex
@@ -5,6 +5,8 @@ defmodule Parrhesia.API.Sync.Manager do
 
   alias Parrhesia.API.Sync
   alias Parrhesia.Protocol.Filter
+  alias Parrhesia.Sync.Transport.WebSockexClient
+  alias Parrhesia.Sync.Worker
 
   require Logger
 
@@ -19,61 +21,63 @@ defmodule Parrhesia.API.Sync.Manager do
     GenServer.start_link(__MODULE__, opts, name: name)
   end
 
-  def put_server(name, server) do
-    GenServer.call(name, {:put_server, server})
-  end
+  def put_server(name, server), do: GenServer.call(name, {:put_server, server})
+  def remove_server(name, server_id), do: GenServer.call(name, {:remove_server, server_id})
+  def get_server(name, server_id), do: GenServer.call(name, {:get_server, server_id})
+  def list_servers(name), do: GenServer.call(name, :list_servers)
+  def start_server(name, server_id), do: GenServer.call(name, {:start_server, server_id})
+  def stop_server(name, server_id), do: GenServer.call(name, {:stop_server, server_id})
+  def sync_now(name, server_id), do: GenServer.call(name, {:sync_now, server_id})
+  def server_stats(name, server_id), do: GenServer.call(name, {:server_stats, server_id})
+  def sync_stats(name), do: GenServer.call(name, :sync_stats)
+  def sync_health(name), do: GenServer.call(name, :sync_health)
 
-  def remove_server(name, server_id) do
-    GenServer.call(name, {:remove_server, server_id})
-  end
-
-  def get_server(name, server_id) do
-    GenServer.call(name, {:get_server, server_id})
-  end
-
-  def list_servers(name) do
-    GenServer.call(name, :list_servers)
-  end
-
-  def start_server(name, server_id) do
-    GenServer.call(name, {:start_server, server_id})
-  end
-
-  def stop_server(name, server_id) do
-    GenServer.call(name, {:stop_server, server_id})
-  end
-
-  def sync_now(name, server_id) do
-    GenServer.call(name, {:sync_now, server_id})
-  end
-
-  def server_stats(name, server_id) do
-    GenServer.call(name, {:server_stats, server_id})
-  end
-
-  def sync_stats(name) do
-    GenServer.call(name, :sync_stats)
-  end
-
-  def sync_health(name) do
-    GenServer.call(name, :sync_health)
+  def runtime_event(name, server_id, kind, attrs \\ %{}) do
+    GenServer.cast(name, {:runtime_event, server_id, kind, attrs})
   end
 
   @impl true
   def init(opts) do
     path = Keyword.get(opts, :path, config_path() || Sync.default_path())
-    {:ok, load_state(path)}
+
+    state =
+      load_state(path)
+      |> Map.merge(%{
+        start_workers?: Keyword.get(opts, :start_workers?, config_value(:start_workers?, true)),
+        worker_supervisor: Keyword.get(opts, :worker_supervisor, Parrhesia.Sync.WorkerSupervisor),
+        worker_registry: Keyword.get(opts, :worker_registry, Parrhesia.Sync.WorkerRegistry),
+        transport_module: Keyword.get(opts, :transport_module, WebSockexClient),
+        relay_info_opts: Keyword.get(opts, :relay_info_opts, []),
+        transport_opts: Keyword.get(opts, :transport_opts, [])
+      })
+
+    {:ok, state, {:continue, :bootstrap}}
+  end
+
+  @impl true
+  def handle_continue(:bootstrap, state) do
+    next_state =
+      if state.start_workers? do
+        state.servers
+        |> Map.keys()
+        |> Enum.reduce(state, fn server_id, acc -> maybe_start_worker(acc, server_id) end)
+      else
+        state
+      end
+
+    {:noreply, next_state}
   end
 
   @impl true
   def handle_call({:put_server, server}, _from, state) do
     case normalize_server(server) do
       {:ok, normalized_server} ->
-        updated_state = put_server_state(state, normalized_server)
+        updated_state =
+          state
+          |> put_server_state(normalized_server)
+          |> persist_and_reconcile!(normalized_server.id)
 
-        with :ok <- persist_state(updated_state) do
-          {:reply, {:ok, merged_server(updated_state, normalized_server.id)}, updated_state}
-        end
+        {:reply, {:ok, merged_server(updated_state, normalized_server.id)}, updated_state}
 
       {:error, reason} ->
         {:reply, {:error, reason}, state}
@@ -82,14 +86,14 @@ defmodule Parrhesia.API.Sync.Manager do
 
   def handle_call({:remove_server, server_id}, _from, state) do
     if Map.has_key?(state.servers, server_id) do
-      updated_state = %{
+      next_state =
         state
-        | servers: Map.delete(state.servers, server_id),
-          runtime: Map.delete(state.runtime, server_id)
-      }
+        |> stop_worker_if_running(server_id)
+        |> Map.update!(:servers, &Map.delete(&1, server_id))
+        |> Map.update!(:runtime, &Map.delete(&1, server_id))
 
-      with :ok <- persist_state(updated_state) do
-        {:reply, :ok, updated_state}
+      with :ok <- persist_state(next_state) do
+        {:reply, :ok, next_state}
       end
     else
       {:reply, {:error, :not_found}, state}
@@ -114,32 +118,69 @@ defmodule Parrhesia.API.Sync.Manager do
   end
 
   def handle_call({:start_server, server_id}, _from, state) do
-    with {:ok, updated_state} <- update_runtime(state, server_id, &mark_running/1),
-         :ok <- persist_state(updated_state) do
-      {:reply, :ok, updated_state}
-    else
-      :error -> {:reply, {:error, :not_found}, state}
-      {:error, reason} -> {:reply, {:error, reason}, state}
+    case Map.fetch(state.runtime, server_id) do
+      {:ok, runtime} ->
+        next_state =
+          state
+          |> put_runtime(server_id, %{runtime | state: :running, last_error: nil})
+          |> persist_and_reconcile!(server_id)
+
+        {:reply, :ok, next_state}
+
+      :error ->
+        {:reply, {:error, :not_found}, state}
     end
   end
 
   def handle_call({:stop_server, server_id}, _from, state) do
-    with {:ok, updated_state} <- update_runtime(state, server_id, &mark_stopped/1),
-         :ok <- persist_state(updated_state) do
-      {:reply, :ok, updated_state}
-    else
-      :error -> {:reply, {:error, :not_found}, state}
-      {:error, reason} -> {:reply, {:error, reason}, state}
+    case Map.fetch(state.runtime, server_id) do
+      {:ok, runtime} ->
+        next_runtime =
+          runtime
+          |> Map.put(:state, :stopped)
+          |> Map.put(:connected?, false)
+          |> Map.put(:last_disconnected_at, now())
+
+        next_state =
+          state
+          |> stop_worker_if_running(server_id)
+          |> put_runtime(server_id, next_runtime)
+
+        with :ok <- persist_state(next_state) do
+          {:reply, :ok, next_state}
+        end
+
+      :error ->
+        {:reply, {:error, :not_found}, state}
     end
   end
 
   def handle_call({:sync_now, server_id}, _from, state) do
-    with {:ok, updated_state} <- update_runtime(state, server_id, &record_sync_now/1),
-         :ok <- persist_state(updated_state) do
-      {:reply, :ok, updated_state}
-    else
-      :error -> {:reply, {:error, :not_found}, state}
-      {:error, reason} -> {:reply, {:error, reason}, state}
+    case {Map.has_key?(state.runtime, server_id), state.start_workers?,
+          lookup_worker(state, server_id)} do
+      {false, _start_workers?, _worker_pid} ->
+        {:reply, {:error, :not_found}, state}
+
+      {true, true, worker_pid} when is_pid(worker_pid) ->
+        Worker.sync_now(worker_pid)
+        {:reply, :ok, state}
+
+      {true, true, nil} ->
+        next_state =
+          state
+          |> put_in([:runtime, server_id, :state], :running)
+          |> persist_and_reconcile!(server_id)
+
+        {:reply, :ok, next_state}
+
+      {true, false, _worker_pid} ->
+        next_state =
+          apply_runtime_event(state, server_id, :sync_started, %{})
+          |> apply_runtime_event(server_id, :sync_completed, %{})
+
+        with :ok <- persist_state(next_state) do
+          {:reply, :ok, next_state}
+        end
     end
   end
 
@@ -150,19 +191,39 @@ defmodule Parrhesia.API.Sync.Manager do
     end
   end
 
-  def handle_call(:sync_stats, _from, state) do
-    {:reply, {:ok, aggregate_stats(state)}, state}
+  def handle_call(:sync_stats, _from, state), do: {:reply, {:ok, aggregate_stats(state)}, state}
+  def handle_call(:sync_health, _from, state), do: {:reply, {:ok, health_summary(state)}, state}
+
+  @impl true
+  def handle_cast({:runtime_event, server_id, kind, attrs}, state) do
+    next_state =
+      state
+      |> apply_runtime_event(server_id, kind, attrs)
+      |> persist_state_if_known_server(server_id)
+
+    {:noreply, next_state}
   end
 
-  def handle_call(:sync_health, _from, state) do
-    {:reply, {:ok, health_summary(state)}, state}
+  defp persist_state_if_known_server(state, server_id) do
+    if Map.has_key?(state.runtime, server_id) do
+      case persist_state(state) do
+        :ok ->
+          state
+
+        {:error, reason} ->
+          Logger.warning("failed to persist sync runtime for #{server_id}: #{inspect(reason)}")
+          state
+      end
+    else
+      state
+    end
   end
 
   defp put_server_state(state, server) do
     runtime =
       case Map.get(state.runtime, server.id) do
         nil -> default_runtime(server)
-        existing_runtime -> maybe_align_runtime_with_server(existing_runtime, server)
+        existing_runtime -> existing_runtime
       end
 
     %{
@@ -172,72 +233,105 @@ defmodule Parrhesia.API.Sync.Manager do
     }
   end
 
-  defp maybe_align_runtime_with_server(runtime, %{enabled?: false}) do
-    runtime
-    |> Map.put(:state, :stopped)
-    |> Map.put(:connected?, false)
-    |> Map.put(:last_disconnected_at, now())
+  defp put_runtime(state, server_id, runtime) do
+    %{state | runtime: Map.put(state.runtime, server_id, runtime)}
   end
 
-  defp maybe_align_runtime_with_server(runtime, _server), do: runtime
-
-  defp default_runtime(server) do
-    %{
-      server_id: server.id,
-      state: if(server.enabled?, do: :running, else: :stopped),
-      connected?: false,
-      last_connected_at: nil,
-      last_disconnected_at: nil,
-      last_sync_started_at: nil,
-      last_sync_completed_at: nil,
-      last_event_received_at: nil,
-      last_eose_at: nil,
-      reconnect_attempts: 0,
-      last_error: nil,
-      events_received: 0,
-      events_accepted: 0,
-      events_duplicate: 0,
-      events_rejected: 0,
-      query_runs: 0,
-      subscription_restarts: 0,
-      reconnects: 0,
-      last_remote_eose_at: nil
-    }
+  defp persist_and_reconcile!(state, server_id) do
+    :ok = persist_state(state)
+    reconcile_worker(state, server_id)
   end
 
-  defp mark_running(runtime) do
-    runtime
-    |> Map.put(:state, :running)
-    |> Map.put(:last_error, nil)
-  end
+  defp reconcile_worker(state, server_id) do
+    cond do
+      not state.start_workers? ->
+        state
 
-  defp mark_stopped(runtime) do
-    runtime
-    |> Map.put(:state, :stopped)
-    |> Map.put(:connected?, false)
-    |> Map.put(:last_disconnected_at, now())
-  end
+      desired_running?(state, server_id) ->
+        state
+        |> stop_worker_if_running(server_id)
+        |> maybe_start_worker(server_id)
 
-  defp record_sync_now(runtime) do
-    sync_timestamp = now()
-
-    runtime
-    |> Map.update!(:query_runs, &(&1 + 1))
-    |> Map.put(:last_sync_started_at, sync_timestamp)
-    |> Map.put(:last_sync_completed_at, sync_timestamp)
-  end
-
-  defp update_runtime(state, server_id, fun) do
-    case Map.fetch(state.runtime, server_id) do
-      {:ok, runtime} ->
-        updated_runtime = fun.(runtime)
-        {:ok, %{state | runtime: Map.put(state.runtime, server_id, updated_runtime)}}
-
-      :error ->
-        :error
+      true ->
+        stop_worker_if_running(state, server_id)
     end
   end
 
+  defp maybe_start_worker(state, server_id) do
+    cond do
+      not state.start_workers? ->
+        state
+
+      not desired_running?(state, server_id) ->
+        state
+
+      lookup_worker(state, server_id) != nil ->
+        state
+
+      true ->
+        server = Map.fetch!(state.servers, server_id)
+        runtime = Map.fetch!(state.runtime, server_id)
+
+        child_spec = %{
+          id: {:sync_worker, server_id},
+          start:
+            {Worker, :start_link,
+             [
+               [
+                 name: via_tuple(server_id, state.worker_registry),
+                 server: server,
+                 runtime: runtime,
+                 manager: self(),
+                 transport_module: state.transport_module,
+                 relay_info_opts: state.relay_info_opts,
+                 transport_opts: state.transport_opts
+               ]
+             ]},
+          restart: :transient
+        }
+
+        case DynamicSupervisor.start_child(state.worker_supervisor, child_spec) do
+          {:ok, _pid} ->
+            state
+
+          {:error, {:already_started, _pid}} ->
+            state
+
+          {:error, reason} ->
+            Logger.warning("failed to start sync worker #{server_id}: #{inspect(reason)}")
+            state
+        end
+    end
+  end
+
+  defp stop_worker_if_running(state, server_id) do
+    if worker_pid = lookup_worker(state, server_id) do
+      _ = Worker.stop(worker_pid)
+    end
+
+    state
+  end
+
+  defp desired_running?(state, server_id) do
+    case Map.fetch(state.runtime, server_id) do
+      {:ok, runtime} -> runtime.state == :running
+      :error -> false
+    end
+  end
+
+  defp lookup_worker(state, server_id) do
+    case Registry.lookup(state.worker_registry, server_id) do
+      [{pid, _value}] -> pid
+      [] -> nil
+    end
+  catch
+    :exit, _reason -> nil
+  end
+
+  defp via_tuple(server_id, registry) do
+    {:via, Registry, {registry, server_id}}
+  end
+
   defp merged_server(state, server_id) do
     state.servers
     |> Map.fetch!(server_id)
@@ -259,7 +353,9 @@ defmodule Parrhesia.API.Sync.Manager do
       "last_sync_started_at" => runtime.last_sync_started_at,
       "last_sync_completed_at" => runtime.last_sync_completed_at,
       "last_remote_eose_at" => runtime.last_remote_eose_at,
-      "last_error" => runtime.last_error
+      "last_error" => runtime.last_error,
+      "cursor_created_at" => runtime.cursor_created_at,
+      "cursor_event_id" => runtime.cursor_event_id
     }
   end
 
@@ -301,6 +397,129 @@ defmodule Parrhesia.API.Sync.Manager do
     }
   end
 
+  defp apply_runtime_event(state, server_id, kind, attrs) do
+    case Map.fetch(state.runtime, server_id) do
+      {:ok, runtime} ->
+        updated_runtime = update_runtime_for_event(runtime, kind, attrs)
+        put_runtime(state, server_id, updated_runtime)
+
+      :error ->
+        state
+    end
+  end
+
+  defp update_runtime_for_event(runtime, :connected, _attrs) do
+    runtime
+    |> Map.put(:state, :running)
+    |> Map.put(:connected?, true)
+    |> Map.put(:last_connected_at, now())
+    |> Map.put(:last_error, nil)
+  end
+
+  defp update_runtime_for_event(runtime, :disconnected, attrs) do
+    reason = format_reason(Map.get(attrs, :reason))
+
+    runtime
+    |> Map.put(:connected?, false)
+    |> Map.put(:last_disconnected_at, now())
+    |> Map.update!(:reconnects, &(&1 + 1))
+    |> Map.put(:last_error, reason)
+  end
+
+  defp update_runtime_for_event(runtime, :error, attrs) do
+    Map.put(runtime, :last_error, format_reason(Map.get(attrs, :reason)))
+  end
+
+  defp update_runtime_for_event(runtime, :sync_started, _attrs) do
+    runtime
+    |> Map.put(:last_sync_started_at, now())
+    |> Map.update!(:query_runs, &(&1 + 1))
+  end
+
+  defp update_runtime_for_event(runtime, :sync_completed, _attrs) do
+    timestamp = now()
+
+    runtime
+    |> Map.put(:last_sync_completed_at, timestamp)
+    |> Map.put(:last_eose_at, timestamp)
+    |> Map.put(:last_remote_eose_at, timestamp)
+  end
+
+  defp update_runtime_for_event(runtime, :subscription_restart, _attrs) do
+    Map.update!(runtime, :subscription_restarts, &(&1 + 1))
+  end
+
+  defp update_runtime_for_event(runtime, :cursor_advanced, attrs) do
+    runtime
+    |> Map.put(:cursor_created_at, Map.get(attrs, :created_at))
+    |> Map.put(:cursor_event_id, Map.get(attrs, :event_id))
+  end
+
+  defp update_runtime_for_event(runtime, :event_result, attrs) do
+    event = Map.get(attrs, :event, %{})
+    result = Map.get(attrs, :result)
+
+    runtime
+    |> Map.update!(:events_received, &(&1 + 1))
+    |> Map.put(:last_event_received_at, now())
+    |> increment_result_counter(result)
+    |> maybe_put_last_error(attrs)
+    |> maybe_advance_runtime_cursor(event, result)
+  end
+
+  defp update_runtime_for_event(runtime, _kind, _attrs), do: runtime
+
+  defp increment_result_counter(runtime, :accepted),
+    do: Map.update!(runtime, :events_accepted, &(&1 + 1))
+
+  defp increment_result_counter(runtime, :duplicate),
+    do: Map.update!(runtime, :events_duplicate, &(&1 + 1))
+
+  defp increment_result_counter(runtime, :rejected),
+    do: Map.update!(runtime, :events_rejected, &(&1 + 1))
+
+  defp increment_result_counter(runtime, _result), do: runtime
+
+  defp maybe_put_last_error(runtime, %{reason: nil}), do: runtime
+
+  defp maybe_put_last_error(runtime, attrs),
+    do: Map.put(runtime, :last_error, format_reason(attrs[:reason]))
+
+  defp maybe_advance_runtime_cursor(runtime, event, result)
+       when result in [:accepted, :duplicate] do
+    created_at = Map.get(event, "created_at")
+    event_id = Map.get(event, "id")
+
+    cond do
+      not is_integer(created_at) or not is_binary(event_id) ->
+        runtime
+
+      is_nil(runtime.cursor_created_at) ->
+        runtime
+        |> Map.put(:cursor_created_at, created_at)
+        |> Map.put(:cursor_event_id, event_id)
+
+      created_at > runtime.cursor_created_at ->
+        runtime
+        |> Map.put(:cursor_created_at, created_at)
+        |> Map.put(:cursor_event_id, event_id)
+
+      created_at == runtime.cursor_created_at and event_id > runtime.cursor_event_id ->
+        runtime
+        |> Map.put(:cursor_created_at, created_at)
+        |> Map.put(:cursor_event_id, event_id)
+
+      true ->
+        runtime
+    end
+  end
+
+  defp maybe_advance_runtime_cursor(runtime, _event, _result), do: runtime
+
+  defp format_reason(nil), do: nil
+  defp format_reason(reason) when is_binary(reason), do: reason
+  defp format_reason(reason), do: inspect(reason)
+
   defp load_state(path) do
     case File.read(path) do
       {:ok, payload} ->
@@ -361,29 +580,29 @@ defmodule Parrhesia.API.Sync.Manager do
   defp normalize_runtime(nil, server), do: default_runtime(server)
 
   defp normalize_runtime(runtime, server) when is_map(runtime) do
-    state =
-      runtime
-      |> Map.put(:server_id, server.id)
-      |> Map.put(:state, normalize_runtime_state(fetch_value(runtime, :state)))
-      |> Map.put(:connected?, fetch_boolean(runtime, :connected?) || false)
-      |> Map.put(:last_connected_at, fetch_string_or_nil(runtime, :last_connected_at))
-      |> Map.put(:last_disconnected_at, fetch_string_or_nil(runtime, :last_disconnected_at))
-      |> Map.put(:last_sync_started_at, fetch_string_or_nil(runtime, :last_sync_started_at))
-      |> Map.put(:last_sync_completed_at, fetch_string_or_nil(runtime, :last_sync_completed_at))
-      |> Map.put(:last_event_received_at, fetch_string_or_nil(runtime, :last_event_received_at))
-      |> Map.put(:last_eose_at, fetch_string_or_nil(runtime, :last_eose_at))
-      |> Map.put(:last_remote_eose_at, fetch_string_or_nil(runtime, :last_remote_eose_at))
-      |> Map.put(:last_error, fetch_string_or_nil(runtime, :last_error))
-      |> Map.put(:reconnect_attempts, fetch_non_neg_integer(runtime, :reconnect_attempts))
-      |> Map.put(:events_received, fetch_non_neg_integer(runtime, :events_received))
-      |> Map.put(:events_accepted, fetch_non_neg_integer(runtime, :events_accepted))
-      |> Map.put(:events_duplicate, fetch_non_neg_integer(runtime, :events_duplicate))
-      |> Map.put(:events_rejected, fetch_non_neg_integer(runtime, :events_rejected))
-      |> Map.put(:query_runs, fetch_non_neg_integer(runtime, :query_runs))
-      |> Map.put(:subscription_restarts, fetch_non_neg_integer(runtime, :subscription_restarts))
-      |> Map.put(:reconnects, fetch_non_neg_integer(runtime, :reconnects))
-
-    maybe_align_runtime_with_server(state, server)
+    %{
+      server_id: server.id,
+      state: normalize_runtime_state(fetch_value(runtime, :state)),
+      connected?: fetch_boolean(runtime, :connected?) || false,
+      last_connected_at: fetch_string_or_nil(runtime, :last_connected_at),
+      last_disconnected_at: fetch_string_or_nil(runtime, :last_disconnected_at),
+      last_sync_started_at: fetch_string_or_nil(runtime, :last_sync_started_at),
+      last_sync_completed_at: fetch_string_or_nil(runtime, :last_sync_completed_at),
+      last_event_received_at: fetch_string_or_nil(runtime, :last_event_received_at),
+      last_eose_at: fetch_string_or_nil(runtime, :last_eose_at),
+      reconnect_attempts: fetch_non_neg_integer(runtime, :reconnect_attempts),
+      last_error: fetch_string_or_nil(runtime, :last_error),
+      events_received: fetch_non_neg_integer(runtime, :events_received),
+      events_accepted: fetch_non_neg_integer(runtime, :events_accepted),
+      events_duplicate: fetch_non_neg_integer(runtime, :events_duplicate),
+      events_rejected: fetch_non_neg_integer(runtime, :events_rejected),
+      query_runs: fetch_non_neg_integer(runtime, :query_runs),
+      subscription_restarts: fetch_non_neg_integer(runtime, :subscription_restarts),
+      reconnects: fetch_non_neg_integer(runtime, :reconnects),
+      last_remote_eose_at: fetch_string_or_nil(runtime, :last_remote_eose_at),
+      cursor_created_at: fetch_optional_integer(runtime, :cursor_created_at),
+      cursor_event_id: fetch_string_or_nil(runtime, :cursor_event_id)
+    }
   end
 
   defp normalize_runtime(_runtime, server), do: default_runtime(server)
@@ -404,7 +623,7 @@ defmodule Parrhesia.API.Sync.Manager do
 
   defp encode_state(state) do
     %{
-      "version" => 1,
+      "version" => 2,
       "servers" =>
         Map.new(state.servers, fn {server_id, server} -> {server_id, encode_server(server)} end),
       "runtime" =>
@@ -457,7 +676,9 @@ defmodule Parrhesia.API.Sync.Manager do
       "query_runs" => runtime.query_runs,
       "subscription_restarts" => runtime.subscription_restarts,
       "reconnects" => runtime.reconnects,
-      "last_remote_eose_at" => runtime.last_remote_eose_at
+      "last_remote_eose_at" => runtime.last_remote_eose_at,
+      "cursor_created_at" => runtime.cursor_created_at,
+      "cursor_event_id" => runtime.cursor_event_id
     }
   end
 
@@ -465,9 +686,35 @@ defmodule Parrhesia.API.Sync.Manager do
     %{path: path, servers: %{}, runtime: %{}}
   end
 
+  defp default_runtime(server) do
+    %{
+      server_id: server.id,
+      state: if(server.enabled?, do: :running, else: :stopped),
+      connected?: false,
+      last_connected_at: nil,
+      last_disconnected_at: nil,
+      last_sync_started_at: nil,
+      last_sync_completed_at: nil,
+      last_event_received_at: nil,
+      last_eose_at: nil,
+      reconnect_attempts: 0,
+      last_error: nil,
+      events_received: 0,
+      events_accepted: 0,
+      events_duplicate: 0,
+      events_rejected: 0,
+      query_runs: 0,
+      subscription_restarts: 0,
+      reconnects: 0,
+      last_remote_eose_at: nil,
+      cursor_created_at: nil,
+      cursor_event_id: nil
+    }
+  end
+
   defp normalize_server(server) when is_map(server) do
     with {:ok, id} <- normalize_non_empty_string(fetch_value(server, :id), :invalid_server_id),
-         {:ok, {url, host}} <- normalize_url(fetch_value(server, :url)),
+         {:ok, {url, host, scheme}} <- normalize_url(fetch_value(server, :url)),
          {:ok, enabled?} <- normalize_boolean(fetch_value(server, :enabled?), true),
          {:ok, auth_pubkey} <- normalize_pubkey(fetch_value(server, :auth_pubkey)),
          {:ok, filters} <- normalize_filters(fetch_value(server, :filters)),
@@ -475,7 +722,7 @@ defmodule Parrhesia.API.Sync.Manager do
          {:ok, overlap_window_seconds} <-
            normalize_overlap_window(fetch_value(server, :overlap_window_seconds)),
          {:ok, auth} <- normalize_auth(fetch_value(server, :auth)),
-         {:ok, tls} <- normalize_tls(fetch_value(server, :tls), host),
+         {:ok, tls} <- normalize_tls(fetch_value(server, :tls), host, scheme),
          {:ok, metadata} <- normalize_metadata(fetch_value(server, :metadata)) do
       {:ok,
        %{
@@ -499,7 +746,7 @@ defmodule Parrhesia.API.Sync.Manager do
     uri = URI.parse(url)
 
     if uri.scheme in ["ws", "wss"] and is_binary(uri.host) and uri.host != "" do
-      {:ok, {URI.to_string(uri), uri.host}}
+      {:ok, {URI.to_string(uri), uri.host, uri.scheme}}
     else
       {:error, :invalid_url}
     end
@@ -556,27 +803,37 @@ defmodule Parrhesia.API.Sync.Manager do
   defp normalize_auth_type("nip42"), do: {:ok, :nip42}
   defp normalize_auth_type(_type), do: {:error, :invalid_auth_type}
 
-  defp normalize_tls(tls, host) when is_map(tls) do
+  defp normalize_tls(tls, host, scheme) when is_map(tls) do
     with {:ok, mode} <- normalize_tls_mode(fetch_value(tls, :mode)),
+         :ok <- validate_tls_mode_against_scheme(mode, scheme),
          {:ok, hostname} <- normalize_hostname(fetch_value(tls, :hostname) || host),
-         {:ok, pins} <- normalize_tls_pins(fetch_value(tls, :pins)) do
+         {:ok, pins} <- normalize_tls_pins(mode, fetch_value(tls, :pins)) do
       {:ok, %{mode: mode, hostname: hostname, pins: pins}}
     end
   end
 
-  defp normalize_tls(_tls, _host), do: {:error, :invalid_tls}
+  defp normalize_tls(_tls, _host, _scheme), do: {:error, :invalid_tls}
 
   defp normalize_tls_mode(nil), do: {:ok, @default_tls_mode}
   defp normalize_tls_mode(:required), do: {:ok, :required}
   defp normalize_tls_mode("required"), do: {:ok, :required}
+  defp normalize_tls_mode(:disabled), do: {:ok, :disabled}
+  defp normalize_tls_mode("disabled"), do: {:ok, :disabled}
   defp normalize_tls_mode(_mode), do: {:error, :invalid_tls_mode}
 
+  defp validate_tls_mode_against_scheme(:required, "wss"), do: :ok
+  defp validate_tls_mode_against_scheme(:required, _scheme), do: {:error, :invalid_url}
+  defp validate_tls_mode_against_scheme(:disabled, _scheme), do: :ok
+
   defp normalize_hostname(hostname) when is_binary(hostname) and hostname != "",
     do: {:ok, hostname}
 
   defp normalize_hostname(_hostname), do: {:error, :invalid_tls_hostname}
 
-  defp normalize_tls_pins(pins) when is_list(pins) and pins != [] do
+  defp normalize_tls_pins(:disabled, nil), do: {:ok, []}
+  defp normalize_tls_pins(:disabled, pins) when is_list(pins), do: {:ok, []}
+
+  defp normalize_tls_pins(:required, pins) when is_list(pins) and pins != [] do
     Enum.reduce_while(pins, {:ok, []}, fn pin, {:ok, acc} ->
       case normalize_tls_pin(pin) do
         {:ok, normalized_pin} -> {:cont, {:ok, [normalized_pin | acc]}}
@@ -589,7 +846,7 @@ defmodule Parrhesia.API.Sync.Manager do
     end
   end
 
-  defp normalize_tls_pins(_pins), do: {:error, :invalid_tls_pins}
+  defp normalize_tls_pins(:required, _pins), do: {:error, :invalid_tls_pins}
 
   defp normalize_tls_pin(pin) when is_map(pin) do
     with {:ok, type} <- normalize_tls_pin_type(fetch_value(pin, :type)),
@@ -639,6 +896,13 @@ defmodule Parrhesia.API.Sync.Manager do
     end
   end
 
+  defp fetch_optional_integer(map, key) do
+    case fetch_value(map, key) do
+      value when is_integer(value) and value >= 0 -> value
+      _other -> nil
+    end
+  end
+
   defp fetch_boolean(map, key) do
     case fetch_value(map, key) do
       value when is_boolean(value) -> value
@@ -658,9 +922,13 @@ defmodule Parrhesia.API.Sync.Manager do
   end
 
   defp config_path do
+    config_value(:path)
+  end
+
+  defp config_value(key, default \\ nil) do
     :parrhesia
     |> Application.get_env(:sync, [])
-    |> Keyword.get(:path)
+    |> Keyword.get(key, default)
   end
 
   defp now do
diff --git a/lib/parrhesia/sync/relay_info_client.ex b/lib/parrhesia/sync/relay_info_client.ex
new file mode 100644
index 0000000..4c1484e
--- /dev/null
+++ b/lib/parrhesia/sync/relay_info_client.ex
@@ -0,0 +1,60 @@
+defmodule Parrhesia.Sync.RelayInfoClient do
+  @moduledoc false
+
+  alias Parrhesia.Sync.TLS
+
+  @spec verify_remote_identity(map(), keyword()) :: :ok | {:error, term()}
+  def verify_remote_identity(server, opts \\ []) do
+    request_fun = Keyword.get(opts, :request_fun, &default_request/2)
+
+    with {:ok, response} <- request_fun.(relay_info_url(server.url), request_opts(server)),
+         {:ok, pubkey} <- extract_pubkey(response) do
+      if pubkey == server.auth_pubkey do
+        :ok
+      else
+        {:error, :remote_identity_mismatch}
+      end
+    end
+  end
+
+  defp default_request(url, opts) do
+    case Req.get(
+           url: url,
+           headers: [{"accept", "application/nostr+json"}],
+           decode_body: false,
+           connect_options: opts
+         ) do
+      {:ok, response} -> {:ok, response}
+      {:error, reason} -> {:error, reason}
+    end
+  end
+
+  defp extract_pubkey(%Req.Response{status: 200, body: body}) when is_binary(body) do
+    with {:ok, payload} <- JSON.decode(body),
+         pubkey when is_binary(pubkey) and pubkey != "" <- Map.get(payload, "pubkey") do
+      {:ok, String.downcase(pubkey)}
+    else
+      nil -> {:error, :missing_remote_identity}
+      {:error, reason} -> {:error, reason}
+      _other -> {:error, :missing_remote_identity}
+    end
+  end
+
+  defp extract_pubkey(%Req.Response{status: status}),
+    do: {:error, {:relay_info_request_failed, status}}
+
+  defp extract_pubkey(_response), do: {:error, :invalid_relay_info}
+
+  defp request_opts(%{tls: %{mode: :disabled}}), do: []
+  defp request_opts(%{tls: tls}), do: TLS.req_connect_options(tls)
+
+  defp relay_info_url(relay_url) do
+    relay_url
+    |> URI.parse()
+    |> Map.update!(:scheme, fn
+      "wss" -> "https"
+      "ws" -> "http"
+    end)
+    |> URI.to_string()
+  end
+end
diff --git a/lib/parrhesia/sync/supervisor.ex b/lib/parrhesia/sync/supervisor.ex
index 5dc83fd..265ef86 100644
--- a/lib/parrhesia/sync/supervisor.ex
+++ b/lib/parrhesia/sync/supervisor.ex
@@ -6,15 +6,38 @@ defmodule Parrhesia.Sync.Supervisor do
   use Supervisor
 
   def start_link(init_arg \\ []) do
-    Supervisor.start_link(__MODULE__, init_arg, name: __MODULE__)
+    name = Keyword.get(init_arg, :name, __MODULE__)
+    Supervisor.start_link(__MODULE__, init_arg, name: name)
   end
 
   @impl true
-  def init(_init_arg) do
+  def init(init_arg) do
+    worker_registry = Keyword.get(init_arg, :worker_registry, Parrhesia.Sync.WorkerRegistry)
+    worker_supervisor = Keyword.get(init_arg, :worker_supervisor, Parrhesia.Sync.WorkerSupervisor)
+    manager_name = Keyword.get(init_arg, :manager, Parrhesia.API.Sync.Manager)
+
     children = [
-      {Parrhesia.API.Sync.Manager, []}
+      {Registry, keys: :unique, name: worker_registry},
+      {DynamicSupervisor, strategy: :one_for_one, name: worker_supervisor},
+      {Parrhesia.API.Sync.Manager,
+       manager_opts(init_arg, manager_name, worker_registry, worker_supervisor)}
     ]
 
     Supervisor.init(children, strategy: :one_for_one)
   end
+
+  defp manager_opts(init_arg, manager_name, worker_registry, worker_supervisor) do
+    [
+      name: manager_name,
+      worker_registry: worker_registry,
+      worker_supervisor: worker_supervisor
+    ] ++
+      Keyword.take(init_arg, [
+        :path,
+        :start_workers?,
+        :transport_module,
+        :relay_info_opts,
+        :transport_opts
+      ])
+  end
 end
diff --git a/lib/parrhesia/sync/tls.ex b/lib/parrhesia/sync/tls.ex
new file mode 100644
index 0000000..1f10d12
--- /dev/null
+++ b/lib/parrhesia/sync/tls.ex
@@ -0,0 +1,88 @@
+defmodule Parrhesia.Sync.TLS do
+  @moduledoc false
+
+  require Record
+
+  Record.defrecordp(
+    :otp_certificate,
+    Record.extract(:OTPCertificate, from_lib: "public_key/include/OTP-PUB-KEY.hrl")
+  )
+
+  Record.defrecordp(
+    :otp_tbs_certificate,
+    Record.extract(:OTPTBSCertificate, from_lib: "public_key/include/OTP-PUB-KEY.hrl")
+  )
+
+  @type tls_config :: %{
+          mode: :required | :disabled,
+          hostname: String.t(),
+          pins: [%{type: :spki_sha256, value: String.t()}]
+        }
+
+  @spec websocket_options(tls_config()) :: keyword()
+  def websocket_options(%{mode: :disabled}), do: [insecure: true]
+
+  def websocket_options(%{mode: :required} = tls) do
+    [
+      ssl_options: transport_opts(tls)
+    ]
+  end
+
+  @spec req_connect_options(tls_config()) :: keyword()
+  def req_connect_options(%{mode: :disabled}), do: []
+
+  def req_connect_options(%{mode: :required} = tls) do
+    [
+      transport_opts: transport_opts(tls)
+    ]
+  end
+
+  def transport_opts(%{hostname: hostname, pins: pins}) do
+    [
+      verify: :verify_peer,
+      cacerts: system_cacerts(),
+      server_name_indication: String.to_charlist(hostname),
+      customize_hostname_check: [
+        match_fun: :public_key.pkix_verify_hostname_match_fun(:https)
+      ],
+      verify_fun:
+        {&verify_certificate/3, %{pins: MapSet.new(Enum.map(pins, & &1.value)), matched?: false}}
+    ]
+  end
+
+  defp verify_certificate(_cert, :valid_peer, %{matched?: true} = state), do: {:valid, state}
+  defp verify_certificate(_cert, :valid_peer, _state), do: {:fail, :pin_mismatch}
+
+  defp verify_certificate(_cert, {:bad_cert, reason}, _state), do: {:fail, reason}
+
+  defp verify_certificate(cert, _event, state) when is_binary(cert) do
+    matched? = MapSet.member?(state.pins, spki_pin(cert))
+    {:valid, %{state | matched?: state.matched? or matched?}}
+  rescue
+    _error -> {:fail, :invalid_certificate}
+  end
+
+  defp verify_certificate(_cert, _event, state), do: {:valid, state}
+
+  defp spki_pin(cert_der) do
+    cert = :public_key.pkix_decode_cert(cert_der, :otp)
+
+    spki =
+      cert
+      |> otp_certificate(:tbsCertificate)
+      |> otp_tbs_certificate(:subjectPublicKeyInfo)
+
+    spki
+    |> :public_key.der_encode(:SubjectPublicKeyInfo)
+    |> then(&:crypto.hash(:sha256, &1))
+    |> Base.encode64()
+  end
+
+  defp system_cacerts do
+    if function_exported?(:public_key, :cacerts_get, 0) do
+      :public_key.cacerts_get()
+    else
+      []
+    end
+  end
+end
diff --git a/lib/parrhesia/sync/transport.ex b/lib/parrhesia/sync/transport.ex
new file mode 100644
index 0000000..10b54af
--- /dev/null
+++ b/lib/parrhesia/sync/transport.ex
@@ -0,0 +1,7 @@
+defmodule Parrhesia.Sync.Transport do
+  @moduledoc false
+
+  @callback connect(pid(), map(), keyword()) :: {:ok, pid()} | {:error, term()}
+  @callback send_json(pid(), term()) :: :ok | {:error, term()}
+  @callback close(pid()) :: :ok
+end
diff --git a/lib/parrhesia/sync/transport/websockex_client.ex b/lib/parrhesia/sync/transport/websockex_client.ex
new file mode 100644
index 0000000..5d091f7
--- /dev/null
+++ b/lib/parrhesia/sync/transport/websockex_client.ex
@@ -0,0 +1,74 @@
+defmodule Parrhesia.Sync.Transport.WebSockexClient do
+  @moduledoc false
+
+  use WebSockex
+
+  alias Parrhesia.Sync.TLS
+
+  @behaviour Parrhesia.Sync.Transport
+
+  @impl true
+  def connect(owner, server, opts \\ []) do
+    state = %{
+      owner: owner,
+      server: server
+    }
+
+    transport_opts =
+      server.tls
+      |> TLS.websocket_options()
+      |> Keyword.merge(Keyword.get(opts, :websocket_opts, []))
+      |> Keyword.put(:handle_initial_conn_failure, true)
+
+    WebSockex.start(server.url, __MODULE__, state, transport_opts)
+  end
+
+  @impl true
+  def send_json(pid, payload) do
+    WebSockex.cast(pid, {:send_json, payload})
+  end
+
+  @impl true
+  def close(pid) do
+    WebSockex.cast(pid, :close)
+    :ok
+  end
+
+  @impl true
+  def handle_connect(conn, state) do
+    send(state.owner, {:sync_transport, self(), :connected, %{resp_headers: conn.resp_headers}})
+    {:ok, state}
+  end
+
+  @impl true
+  def handle_frame({:text, payload}, state) do
+    message =
+      case JSON.decode(payload) do
+        {:ok, frame} -> frame
+        {:error, reason} -> {:decode_error, reason, payload}
+      end
+
+    send(state.owner, {:sync_transport, self(), :frame, message})
+    {:ok, state}
+  end
+
+  def handle_frame(frame, state) do
+    send(state.owner, {:sync_transport, self(), :frame, frame})
+    {:ok, state}
+  end
+
+  @impl true
+  def handle_cast({:send_json, payload}, state) do
+    {:reply, {:text, JSON.encode!(payload)}, state}
+  end
+
+  def handle_cast(:close, state) do
+    {:close, state}
+  end
+
+  @impl true
+  def handle_disconnect(status, state) do
+    send(state.owner, {:sync_transport, self(), :disconnected, status})
+    {:ok, state}
+  end
+end
diff --git a/lib/parrhesia/sync/worker.ex b/lib/parrhesia/sync/worker.ex
new file mode 100644
index 0000000..56d3f54
--- /dev/null
+++ b/lib/parrhesia/sync/worker.ex
@@ -0,0 +1,367 @@
+defmodule Parrhesia.Sync.Worker do
+  @moduledoc false
+
+  use GenServer
+
+  alias Parrhesia.API.Events
+  alias Parrhesia.API.Identity
+  alias Parrhesia.API.RequestContext
+  alias Parrhesia.API.Sync.Manager
+  alias Parrhesia.Sync.RelayInfoClient
+  alias Parrhesia.Sync.Transport.WebSockexClient
+
+  @initial_backoff_ms 1_000
+  @max_backoff_ms 30_000
+  @auth_kind 22_242
+
+  defstruct server: nil,
+            manager: nil,
+            transport_module: WebSockexClient,
+            transport_pid: nil,
+            phase: :idle,
+            current_subscription_id: nil,
+            backoff_ms: @initial_backoff_ms,
+            authenticated?: false,
+            auth_event_id: nil,
+            resubscribe_after_auth?: false,
+            cursor_created_at: nil,
+            cursor_event_id: nil,
+            relay_info_opts: [],
+            transport_opts: []
+
+  @type t :: %__MODULE__{}
+
+  def child_spec(opts) do
+    server = Keyword.fetch!(opts, :server)
+
+    %{
+      id: {:sync_worker, server.id},
+      start: {__MODULE__, :start_link, [opts]},
+      restart: :transient
+    }
+  end
+
+  def start_link(opts) do
+    name = Keyword.get(opts, :name)
+    GenServer.start_link(__MODULE__, opts, name: name)
+  end
+
+  def sync_now(worker), do: GenServer.cast(worker, :sync_now)
+  def stop(worker), do: GenServer.stop(worker, :normal)
+
+  @impl true
+  def init(opts) do
+    server = Keyword.fetch!(opts, :server)
+    runtime = Keyword.get(opts, :runtime, %{})
+
+    state = %__MODULE__{
+      server: server,
+      manager: Keyword.fetch!(opts, :manager),
+      transport_module: Keyword.get(opts, :transport_module, WebSockexClient),
+      cursor_created_at: Map.get(runtime, :cursor_created_at),
+      cursor_event_id: Map.get(runtime, :cursor_event_id),
+      relay_info_opts: Keyword.get(opts, :relay_info_opts, []),
+      transport_opts: Keyword.get(opts, :transport_opts, [])
+    }
+
+    send(self(), :connect)
+    {:ok, state}
+  end
+
+  @impl true
+  def handle_cast(:sync_now, state) do
+    Manager.runtime_event(state.manager, state.server.id, :subscription_restart)
+
+    next_state =
+      state
+      |> close_subscription()
+      |> issue_subscription()
+
+    {:noreply, next_state}
+  end
+
+  @impl true
+  def handle_info(:connect, %__MODULE__{transport_pid: nil} = state) do
+    case RelayInfoClient.verify_remote_identity(state.server, state.relay_info_opts) do
+      :ok ->
+        connect_transport(state)
+
+      {:error, reason} ->
+        Manager.runtime_event(state.manager, state.server.id, :disconnected, %{reason: reason})
+        {:noreply, schedule_reconnect(state)}
+    end
+  end
+
+  def handle_info(:connect, state), do: {:noreply, state}
+
+  def handle_info({:sync_transport, transport_pid, :connected, _info}, state) do
+    Manager.runtime_event(state.manager, state.server.id, :connected, %{})
+
+    next_state =
+      state
+      |> Map.put(:transport_pid, transport_pid)
+      |> Map.put(:backoff_ms, @initial_backoff_ms)
+      |> Map.put(:authenticated?, false)
+      |> Map.put(:auth_event_id, nil)
+      |> Map.put(:resubscribe_after_auth?, false)
+      |> issue_subscription()
+
+    {:noreply, next_state}
+  end
+
+  def handle_info({:sync_transport, _transport_pid, :frame, frame}, state) do
+    {:noreply, handle_transport_frame(state, frame)}
+  end
+
+  def handle_info({:sync_transport, _transport_pid, :disconnected, status}, state) do
+    Manager.runtime_event(state.manager, state.server.id, :disconnected, %{reason: status.reason})
+
+    next_state =
+      state
+      |> Map.put(:transport_pid, nil)
+      |> Map.put(:phase, :idle)
+      |> Map.put(:authenticated?, false)
+      |> Map.put(:auth_event_id, nil)
+      |> Map.put(:resubscribe_after_auth?, false)
+      |> Map.put(:current_subscription_id, nil)
+      |> schedule_reconnect()
+
+    {:noreply, next_state}
+  end
+
+  def handle_info(_message, state), do: {:noreply, state}
+
+  defp connect_transport(state) do
+    case state.transport_module.connect(self(), state.server, state.transport_opts) do
+      {:ok, transport_pid} ->
+        {:noreply, %{state | transport_pid: transport_pid, phase: :connecting}}
+
+      {:error, reason} ->
+        Manager.runtime_event(state.manager, state.server.id, :disconnected, %{reason: reason})
+        {:noreply, schedule_reconnect(state)}
+    end
+  end
+
+  defp handle_transport_frame(state, ["AUTH", challenge]) when is_binary(challenge) do
+    case send_auth_event(state, challenge) do
+      {:ok, auth_event_id} ->
+        %{state | auth_event_id: auth_event_id, phase: :authenticating}
+
+      {:error, reason} ->
+        Manager.runtime_event(state.manager, state.server.id, :error, %{reason: reason})
+        state
+    end
+  end
+
+  defp handle_transport_frame(state, ["OK", event_id, true, _message])
+       when event_id == state.auth_event_id do
+    next_state = %{state | authenticated?: true, auth_event_id: nil}
+
+    if next_state.resubscribe_after_auth? do
+      next_state
+      |> Map.put(:resubscribe_after_auth?, false)
+      |> issue_subscription()
+    else
+      next_state
+    end
+  end
+
+  defp handle_transport_frame(state, ["OK", event_id, false, message])
+       when event_id == state.auth_event_id do
+    Manager.runtime_event(state.manager, state.server.id, :error, %{reason: message})
+    schedule_reconnect(%{state | auth_event_id: nil, authenticated?: false})
+  end
+
+  defp handle_transport_frame(state, ["EVENT", subscription_id, event])
+       when subscription_id == state.current_subscription_id and is_map(event) do
+    handle_remote_event(state, event)
+  end
+
+  defp handle_transport_frame(state, ["EOSE", subscription_id])
+       when subscription_id == state.current_subscription_id do
+    Manager.runtime_event(state.manager, state.server.id, :sync_completed, %{})
+    %{state | phase: :streaming}
+  end
+
+  defp handle_transport_frame(state, ["CLOSED", subscription_id, message])
+       when subscription_id == state.current_subscription_id do
+    auth_required? = is_binary(message) and String.contains?(String.downcase(message), "auth")
+
+    next_state =
+      state
+      |> Map.put(:current_subscription_id, nil)
+      |> Map.put(:phase, :idle)
+
+    if auth_required? and not state.authenticated? do
+      %{next_state | resubscribe_after_auth?: true}
+    else
+      Manager.runtime_event(state.manager, state.server.id, :error, %{reason: message})
+      schedule_reconnect(next_state)
+    end
+  end
+
+  defp handle_transport_frame(state, {:decode_error, reason, _payload}) do
+    Manager.runtime_event(state.manager, state.server.id, :error, %{reason: reason})
+    state
+  end
+
+  defp handle_transport_frame(state, _frame), do: state
+
+  defp issue_subscription(%__MODULE__{transport_pid: nil} = state), do: state
+
+  defp issue_subscription(state) do
+    subscription_id = subscription_id(state.server.id)
+    filters = sync_filters(state)
+
+    :ok =
+      state.transport_module.send_json(state.transport_pid, ["REQ", subscription_id | filters])
+
+    Manager.runtime_event(state.manager, state.server.id, :sync_started, %{})
+
+    %{
+      state
+      | current_subscription_id: subscription_id,
+        phase: :catchup
+    }
+  end
+
+  defp close_subscription(%__MODULE__{transport_pid: nil} = state), do: state
+  defp close_subscription(%__MODULE__{current_subscription_id: nil} = state), do: state
+
+  defp close_subscription(state) do
+    :ok =
+      state.transport_module.send_json(state.transport_pid, [
+        "CLOSE",
+        state.current_subscription_id
+      ])
+
+    %{state | current_subscription_id: nil}
+  end
+
+  defp send_auth_event(state, challenge) do
+    event = %{
+      "created_at" => System.system_time(:second),
+      "kind" => @auth_kind,
+      "tags" => [["challenge", challenge], ["relay", state.server.url]],
+      "content" => ""
+    }
+
+    with {:ok, signed_event} <- Identity.sign_event(event) do
+      :ok = state.transport_module.send_json(state.transport_pid, ["AUTH", signed_event])
+      {:ok, signed_event["id"]}
+    end
+  end
+
+  defp handle_remote_event(state, event) do
+    context = request_context(state)
+
+    case Events.publish(event, context: context) do
+      {:ok, %{accepted: true}} ->
+        Manager.runtime_event(state.manager, state.server.id, :event_result, %{
+          result: :accepted,
+          event: event
+        })
+
+        advance_cursor(state, event)
+
+      {:ok, %{accepted: false, reason: :duplicate_event}} ->
+        Manager.runtime_event(state.manager, state.server.id, :event_result, %{
+          result: :duplicate,
+          event: event
+        })
+
+        advance_cursor(state, event)
+
+      {:ok, %{accepted: false, reason: reason}} ->
+        Manager.runtime_event(state.manager, state.server.id, :event_result, %{
+          result: :rejected,
+          event: event,
+          reason: reason
+        })
+
+        state
+
+      {:error, reason} ->
+        Manager.runtime_event(state.manager, state.server.id, :event_result, %{
+          result: :rejected,
+          event: event,
+          reason: reason
+        })
+
+        state
+    end
+  end
+
+  defp request_context(state) do
+    %RequestContext{
+      authenticated_pubkeys: MapSet.new([state.server.auth_pubkey]),
+      caller: :sync,
+      subscription_id: state.current_subscription_id,
+      peer_id: state.server.id,
+      metadata: %{
+        sync_server_id: state.server.id,
+        remote_url: state.server.url
+      }
+    }
+  end
+
+  defp advance_cursor(state, event) do
+    created_at = Map.get(event, "created_at")
+    event_id = Map.get(event, "id")
+
+    if newer_cursor?(state.cursor_created_at, state.cursor_event_id, created_at, event_id) do
+      Manager.runtime_event(state.manager, state.server.id, :cursor_advanced, %{
+        created_at: created_at,
+        event_id: event_id
+      })
+
+      %{state | cursor_created_at: created_at, cursor_event_id: event_id}
+    else
+      state
+    end
+  end
+
+  defp newer_cursor?(nil, _cursor_event_id, created_at, event_id),
+    do: is_integer(created_at) and is_binary(event_id)
+
+  defp newer_cursor?(cursor_created_at, cursor_event_id, created_at, event_id) do
+    cond do
+      not is_integer(created_at) or not is_binary(event_id) ->
+        false
+
+      created_at > cursor_created_at ->
+        true
+
+      created_at == cursor_created_at and is_binary(cursor_event_id) and
+          event_id > cursor_event_id ->
+        true
+
+      true ->
+        false
+    end
+  end
+
+  defp sync_filters(state) do
+    Enum.map(state.server.filters, fn filter ->
+      case since_value(state, filter) do
+        nil -> filter
+        since -> Map.put(filter, "since", since)
+      end
+    end)
+  end
+
+  defp since_value(%__MODULE__{cursor_created_at: nil}, _filter), do: nil
+
+  defp since_value(state, _filter) do
+    max(state.cursor_created_at - state.server.overlap_window_seconds, 0)
+  end
+
+  defp schedule_reconnect(state) do
+    Process.send_after(self(), :connect, state.backoff_ms)
+    %{state | backoff_ms: min(state.backoff_ms * 2, @max_backoff_ms)}
+  end
+
+  defp subscription_id(server_id) do
+    "sync-#{server_id}-#{System.unique_integer([:positive, :monotonic])}"
+  end
+end
diff --git a/lib/parrhesia/test_support/sync_fake_relay/plug.ex b/lib/parrhesia/test_support/sync_fake_relay/plug.ex
new file mode 100644
index 0000000..f70c78a
--- /dev/null
+++ b/lib/parrhesia/test_support/sync_fake_relay/plug.ex
@@ -0,0 +1,49 @@
+defmodule Parrhesia.TestSupport.SyncFakeRelay.Plug do
+  @moduledoc false
+
+  import Plug.Conn
+
+  alias Parrhesia.TestSupport.SyncFakeRelay.Server
+
+  def init(opts), do: opts
+
+  def call(conn, opts) do
+    server = Keyword.fetch!(opts, :server)
+
+    cond do
+      conn.request_path == "/relay" and wants_nip11?(conn) ->
+        send_json(conn, 200, Server.document(server))
+
+      conn.request_path == "/relay" ->
+        conn
+        |> WebSockAdapter.upgrade(
+          Parrhesia.TestSupport.SyncFakeRelay.Socket,
+          %{server: server, relay_url: relay_url(conn)},
+          timeout: 60_000
+        )
+        |> halt()
+
+      true ->
+        send_resp(conn, 404, "not found")
+    end
+  end
+
+  defp wants_nip11?(conn) do
+    conn
+    |> get_req_header("accept")
+    |> Enum.any?(&String.contains?(&1, "application/nostr+json"))
+  end
+
+  defp send_json(conn, status, body) do
+    encoded = JSON.encode!(body)
+
+    conn
+    |> put_resp_content_type("application/nostr+json")
+    |> send_resp(status, encoded)
+  end
+
+  defp relay_url(conn) do
+    scheme = if conn.scheme == :https, do: "wss", else: "ws"
+    "#{scheme}://#{conn.host}:#{conn.port}#{conn.request_path}"
+  end
+end
diff --git a/lib/parrhesia/test_support/sync_fake_relay/server.ex b/lib/parrhesia/test_support/sync_fake_relay/server.ex
new file mode 100644
index 0000000..f9c45af
--- /dev/null
+++ b/lib/parrhesia/test_support/sync_fake_relay/server.ex
@@ -0,0 +1,65 @@
+defmodule Parrhesia.TestSupport.SyncFakeRelay.Server do
+  @moduledoc false
+
+  use Agent
+
+  def start_link(opts) do
+    name = Keyword.fetch!(opts, :name)
+
+    initial_state = %{
+      pubkey: Keyword.fetch!(opts, :pubkey),
+      expected_client_pubkey: Keyword.fetch!(opts, :expected_client_pubkey),
+      initial_events: Keyword.get(opts, :initial_events, []),
+      subscribers: %{}
+    }
+
+    Agent.start_link(fn -> initial_state end, name: name)
+  end
+
+  def document(server) do
+    Agent.get(server, fn state ->
+      %{
+        "name" => "Sync Fake Relay",
+        "description" => "test relay",
+        "pubkey" => state.pubkey,
+        "supported_nips" => [1, 11, 42]
+      }
+    end)
+  end
+
+  def initial_events(server) do
+    Agent.get(server, & &1.initial_events)
+  end
+
+  def expected_client_pubkey(server) do
+    Agent.get(server, & &1.expected_client_pubkey)
+  end
+
+  def register_subscription(server, pid, subscription_id) do
+    Agent.update(server, fn state ->
+      put_in(state, [:subscribers, {pid, subscription_id}], true)
+    end)
+  end
+
+  def unregister_subscription(server, pid, subscription_id) do
+    Agent.update(server, fn state ->
+      update_in(state.subscribers, &Map.delete(&1, {pid, subscription_id}))
+    end)
+  end
+
+  def publish_live_event(server, event) do
+    subscribers =
+      Agent.get_and_update(server, fn state ->
+        {
+          Map.keys(state.subscribers),
+          %{state | initial_events: state.initial_events ++ [event]}
+        }
+      end)
+
+    Enum.each(subscribers, fn {pid, subscription_id} ->
+      send(pid, {:sync_fake_relay_event, subscription_id, event})
+    end)
+
+    :ok
+  end
+end
diff --git a/lib/parrhesia/test_support/sync_fake_relay/socket.ex b/lib/parrhesia/test_support/sync_fake_relay/socket.ex
new file mode 100644
index 0000000..072c065
--- /dev/null
+++ b/lib/parrhesia/test_support/sync_fake_relay/socket.ex
@@ -0,0 +1,118 @@
+defmodule Parrhesia.TestSupport.SyncFakeRelay.Socket do
+  @moduledoc false
+
+  @behaviour WebSock
+
+  alias Parrhesia.TestSupport.SyncFakeRelay.Server
+
+  def init(state), do: {:ok, Map.put(state, :authenticated?, false)}
+
+  def handle_in({payload, [opcode: :text]}, state) do
+    case JSON.decode(payload) do
+      {:ok, ["REQ", subscription_id | _filters]} ->
+        maybe_authorize_req(state, subscription_id)
+
+      {:ok, ["AUTH", auth_event]} when is_map(auth_event) ->
+        handle_auth(auth_event, state)
+
+      {:ok, ["CLOSE", subscription_id]} ->
+        Server.unregister_subscription(state.server, self(), subscription_id)
+
+        {:push, {:text, JSON.encode!(["CLOSED", subscription_id, "error: subscription closed"])},
+         state}
+
+      _other ->
+        {:ok, state}
+    end
+  end
+
+  def handle_in(_frame, state), do: {:ok, state}
+
+  def handle_info({:sync_fake_relay_event, subscription_id, event}, state) do
+    {:push, {:text, JSON.encode!(["EVENT", subscription_id, event])}, state}
+  end
+
+  def handle_info(_message, state), do: {:ok, state}
+
+  def terminate(_reason, state) do
+    Enum.each(Map.get(state, :subscriptions, []), fn subscription_id ->
+      Server.unregister_subscription(state.server, self(), subscription_id)
+    end)
+
+    :ok
+  end
+
+  defp maybe_authorize_req(%{authenticated?: true} = state, subscription_id) do
+    Server.register_subscription(state.server, self(), subscription_id)
+
+    frames =
+      Server.initial_events(state.server)
+      |> Enum.map(fn event -> {:text, JSON.encode!(["EVENT", subscription_id, event])} end)
+      |> Kernel.++([{:text, JSON.encode!(["EOSE", subscription_id])}])
+
+    next_state =
+      state
+      |> Map.update(:subscriptions, [subscription_id], &[subscription_id | &1])
+
+    {:push, frames, next_state}
+  end
+
+  defp maybe_authorize_req(state, subscription_id) do
+    challenge = Base.encode16(:crypto.strong_rand_bytes(12), case: :lower)
+
+    next_state =
+      state
+      |> Map.put(:challenge, challenge)
+      |> Map.put(:pending_subscription_id, subscription_id)
+
+    {:push,
+     [
+       {:text, JSON.encode!(["AUTH", challenge])},
+       {:text,
+        JSON.encode!(["CLOSED", subscription_id, "auth-required: sync access requires AUTH"])}
+     ], next_state}
+  end
+
+  defp handle_auth(auth_event, state) do
+    challenge_ok? = has_tag?(auth_event, "challenge", state.challenge)
+    relay_ok? = has_tag?(auth_event, "relay", state.relay_url)
+    pubkey_ok? = Map.get(auth_event, "pubkey") == Server.expected_client_pubkey(state.server)
+
+    if challenge_ok? and relay_ok? and pubkey_ok? do
+      accepted_state = %{state | authenticated?: true}
+      ok_frame = ["OK", Map.get(auth_event, "id"), true, "ok: auth accepted"]
+
+      if subscription_id = Map.get(accepted_state, :pending_subscription_id) do
+        next_state =
+          accepted_state
+          |> Map.delete(:pending_subscription_id)
+          |> Map.update(:subscriptions, [subscription_id], &[subscription_id | &1])
+
+        Server.register_subscription(state.server, self(), subscription_id)
+
+        {:push,
+         [{:text, JSON.encode!(ok_frame)} | auth_success_frames(accepted_state, subscription_id)],
+         next_state}
+      else
+        {:push, {:text, JSON.encode!(ok_frame)}, accepted_state}
+      end
+    else
+      {:push,
+       {:text, JSON.encode!(["OK", Map.get(auth_event, "id"), false, "invalid: auth rejected"])},
+       state}
+    end
+  end
+
+  defp auth_success_frames(state, subscription_id) do
+    Server.initial_events(state.server)
+    |> Enum.map(fn event -> {:text, JSON.encode!(["EVENT", subscription_id, event])} end)
+    |> Kernel.++([{:text, JSON.encode!(["EOSE", subscription_id])}])
+  end
+
+  defp has_tag?(event, name, expected_value) do
+    Enum.any?(Map.get(event, "tags", []), fn
+      [^name, ^expected_value | _rest] -> true
+      _other -> false
+    end)
+  end
+end
diff --git a/lib/parrhesia/web/relay_info.ex b/lib/parrhesia/web/relay_info.ex
index 3f38938..79d2f82 100644
--- a/lib/parrhesia/web/relay_info.ex
+++ b/lib/parrhesia/web/relay_info.ex
@@ -3,12 +3,14 @@ defmodule Parrhesia.Web.RelayInfo do
   NIP-11 relay information document.
   """
 
+  alias Parrhesia.API.Identity
+
   @spec document() :: map()
   def document do
     %{
       "name" => "Parrhesia",
       "description" => "Nostr/Marmot relay",
-      "pubkey" => nil,
+      "pubkey" => relay_pubkey(),
       "supported_nips" => supported_nips(),
       "software" => "https://git.teralink.net/self/parrhesia",
       "version" => Application.spec(:parrhesia, :vsn) |> to_string(),
@@ -44,4 +46,11 @@ defmodule Parrhesia.Web.RelayInfo do
     |> Application.get_env(:features, [])
     |> Keyword.get(:nip_77_negentropy, true)
   end
+
+  defp relay_pubkey do
+    case Identity.get() do
+      {:ok, %{pubkey: pubkey}} -> pubkey
+      {:error, _reason} -> nil
+    end
+  end
 end
diff --git a/mix.exs b/mix.exs
index 1533ded..cdb92c3 100644
--- a/mix.exs
+++ b/mix.exs
@@ -44,7 +44,7 @@ defmodule Parrhesia.MixProject do
 
       # Test tooling
       {:stream_data, "~> 1.0", only: :test},
-      {:websockex, "~> 0.4", only: :test},
+      {:websockex, "~> 0.4"},
 
       # Project tooling
       {:credo, "~> 1.7", only: [:dev, :test], runtime: false},
diff --git a/test/parrhesia/api/sync_test.exs b/test/parrhesia/api/sync_test.exs
index c6b3978..ccde79f 100644
--- a/test/parrhesia/api/sync_test.exs
+++ b/test/parrhesia/api/sync_test.exs
@@ -128,7 +128,7 @@ defmodule Parrhesia.API.SyncTest do
   defp start_sync_manager do
     path = unique_sync_path()
     manager = {:global, {:sync_manager, System.unique_integer([:positive, :monotonic])}}
-    pid = start_supervised!({Manager, name: manager, path: path})
+    pid = start_supervised!({Manager, name: manager, path: path, start_workers?: false})
 
     {manager, path, pid}
   end
diff --git a/test/parrhesia/sync/worker_test.exs b/test/parrhesia/sync/worker_test.exs
new file mode 100644
index 0000000..022f7c8
--- /dev/null
+++ b/test/parrhesia/sync/worker_test.exs
@@ -0,0 +1,260 @@
+defmodule Parrhesia.Sync.WorkerTest do
+  use ExUnit.Case, async: false
+
+  alias Ecto.Adapters.SQL.Sandbox
+  alias Parrhesia.API.ACL
+  alias Parrhesia.API.Events
+  alias Parrhesia.API.Identity
+  alias Parrhesia.API.RequestContext
+  alias Parrhesia.API.Sync
+  alias Parrhesia.Protocol.EventValidator
+  alias Parrhesia.Repo
+  alias Parrhesia.Sync.Supervisor
+  alias Parrhesia.TestSupport.SyncFakeRelay.Plug
+  alias Parrhesia.TestSupport.SyncFakeRelay.Server
+
+  setup do
+    :ok = Sandbox.checkout(Repo)
+    Sandbox.mode(Repo, {:shared, self()})
+
+    on_exit(fn ->
+      Sandbox.mode(Repo, :manual)
+    end)
+
+    :ok
+  end
+
+  test "req_stream worker verifies remote identity, authenticates, syncs catch-up, streams live, and sync_now reruns catch-up" do
+    {:ok, %{pubkey: local_pubkey}} = Identity.ensure()
+    remote_pubkey = String.duplicate("b", 64)
+    initial_event = valid_sync_event("initial-sync", 1_762_000_000)
+    live_event = valid_sync_event("live-sync", 1_762_000_100)
+
+    relay_server =
+      start_supervised!(
+        {Server,
+         name: unique_name("FakeRelayServer"),
+         pubkey: remote_pubkey,
+         expected_client_pubkey: local_pubkey,
+         initial_events: [initial_event]}
+      )
+
+    port = free_port()
+
+    start_supervised!(
+      {Bandit, plug: {Plug, server: relay_server}, ip: {127, 0, 0, 1}, port: port}
+    )
+
+    relay_url = "ws://127.0.0.1:#{port}/relay"
+    wait_for_relay(relay_url, remote_pubkey)
+
+    assert :ok =
+             ACL.grant(%{
+               principal_type: :pubkey,
+               principal: remote_pubkey,
+               capability: :sync_write,
+               match: %{"kinds" => [5000], "#r" => ["tribes.accounts.user"]}
+             })
+
+    assert :ok =
+             ACL.grant(%{
+               principal_type: :pubkey,
+               principal: remote_pubkey,
+               capability: :sync_read,
+               match: %{"kinds" => [5000], "#r" => ["tribes.accounts.user"]}
+             })
+
+    {manager_name, _supervisor_name} = start_sync_runtime()
+
+    assert {:ok, _server} =
+             Sync.put_server(
+               %{
+                 "id" => "fake-relay",
+                 "url" => relay_url,
+                 "enabled?" => true,
+                 "auth_pubkey" => remote_pubkey,
+                 "filters" => [%{"kinds" => [5000], "#r" => ["tribes.accounts.user"]}],
+                 "tls" => %{"mode" => "disabled", "pins" => []}
+               },
+               manager: manager_name
+             )
+
+    assert_event_synced(initial_event, remote_pubkey)
+
+    assert :ok = Server.publish_live_event(relay_server, live_event)
+    assert_event_synced(live_event, remote_pubkey)
+
+    assert {:ok, stats_before_sync_now} = Sync.sync_stats(manager: manager_name)
+    assert stats_before_sync_now["events_accepted"] >= 2
+
+    assert :ok = Sync.sync_now("fake-relay", manager: manager_name)
+
+    assert_eventually(fn ->
+      case Sync.sync_stats(manager: manager_name) do
+        {:ok, stats} -> stats["query_runs"] >= 2 and stats["subscription_restarts"] >= 1
+        _other -> false
+      end
+    end)
+
+    assert {:ok, health} = Sync.sync_health(manager: manager_name)
+    assert health["status"] == "ok"
+    assert health["servers_connected"] == 1
+  end
+
+  test "worker marks remote identity mismatches as failing health" do
+    {:ok, %{pubkey: local_pubkey}} = Identity.ensure()
+
+    relay_server =
+      start_supervised!(
+        {Server,
+         name: unique_name("MismatchRelayServer"),
+         pubkey: String.duplicate("d", 64),
+         expected_client_pubkey: local_pubkey,
+         initial_events: []}
+      )
+
+    port = free_port()
+
+    start_supervised!(
+      {Bandit, plug: {Plug, server: relay_server}, ip: {127, 0, 0, 1}, port: port}
+    )
+
+    relay_url = "ws://127.0.0.1:#{port}/relay"
+    wait_for_relay(relay_url, String.duplicate("d", 64))
+
+    {manager_name, _supervisor_name} = start_sync_runtime()
+
+    assert {:ok, _server} =
+             Sync.put_server(
+               %{
+                 "id" => "mismatch-relay",
+                 "url" => relay_url,
+                 "enabled?" => true,
+                 "auth_pubkey" => String.duplicate("e", 64),
+                 "filters" => [%{"kinds" => [5000], "#r" => ["tribes.accounts.user"]}],
+                 "tls" => %{"mode" => "disabled", "pins" => []}
+               },
+               manager: manager_name
+             )
+
+    assert_eventually(fn ->
+      case Sync.sync_health(manager: manager_name) do
+        {:ok, %{"status" => "degraded", "servers_failing" => servers}} ->
+          Enum.any?(
+            servers,
+            &(&1["id"] == "mismatch-relay" and &1["reason"] == ":remote_identity_mismatch")
+          )
+
+        _other ->
+          false
+      end
+    end)
+  end
+
+  defp start_sync_runtime do
+    manager_name = unique_name("SyncManager")
+    worker_registry = unique_name("SyncRegistry")
+    worker_supervisor = unique_name("SyncWorkerSupervisor")
+    supervisor_name = unique_name("SyncSupervisor")
+
+    start_supervised!(
+      {Supervisor,
+       name: supervisor_name,
+       manager: manager_name,
+       worker_registry: worker_registry,
+       worker_supervisor: worker_supervisor,
+       path: unique_sync_path(),
+       start_workers?: true}
+    )
+
+    {manager_name, supervisor_name}
+  end
+
+  defp assert_event_synced(event, remote_pubkey) do
+    assert_eventually(fn ->
+      case Events.query(
+             [%{"ids" => [event["id"]]}],
+             context: %RequestContext{
+               authenticated_pubkeys: MapSet.new([remote_pubkey])
+             }
+           ) do
+        {:ok, [stored_event]} -> stored_event["id"] == event["id"]
+        _other -> false
+      end
+    end)
+  end
+
+  defp wait_for_relay(relay_url, expected_pubkey) do
+    info_url =
+      relay_url
+      |> String.replace_prefix("ws://", "http://")
+      |> String.replace_prefix("wss://", "https://")
+
+    assert_eventually(fn ->
+      with {:ok, %{status: 200, body: body}} <-
+             Req.get(
+               url: info_url,
+               headers: [{"accept", "application/nostr+json"}],
+               decode_body: false
+             ),
+           {:ok, %{"pubkey" => ^expected_pubkey}} <- JSON.decode(body) do
+        true
+      else
+        _other -> false
+      end
+    end)
+  end
+
+  defp valid_sync_event(content, created_at) do
+    base_event = %{
+      "pubkey" => String.duplicate("f", 64),
+      "created_at" => created_at,
+      "kind" => 5000,
+      "tags" => [["r", "tribes.accounts.user"]],
+      "content" => content,
+      "sig" => String.duplicate("0", 128)
+    }
+
+    Map.put(base_event, "id", EventValidator.compute_id(base_event))
+  end
+
+  defp free_port do
+    {:ok, socket} = :gen_tcp.listen(0, [:binary, active: false, packet: :raw, reuseaddr: true])
+    {:ok, port} = :inet.port(socket)
+    :ok = :gen_tcp.close(socket)
+    port
+  end
+
+  defp unique_name(prefix) do
+    :"#{prefix}_#{System.unique_integer([:positive, :monotonic])}"
+  end
+
+  defp unique_sync_path do
+    path =
+      Path.join(
+        System.tmp_dir!(),
+        "parrhesia_sync_runtime_#{System.unique_integer([:positive, :monotonic])}.json"
+      )
+
+    on_exit(fn ->
+      _ = File.rm(path)
+    end)
+
+    path
+  end
+
+  defp assert_eventually(fun, attempts \\ 50)
+
+  defp assert_eventually(_fun, 0), do: flunk("condition was not met in time")
+
+  defp assert_eventually(fun, attempts) do
+    if fun.() do
+      :ok
+    else
+      receive do
+      after
+        50 -> assert_eventually(fun, attempts - 1)
+      end
+    end
+  end
+end