docs: say where async waits with no worker

CHANGELOG.md

@@ -2,6 +2,16 @@
 
 ## Unreleased
 
+- State where `async` waits when no worker runs. The `async` section of the
+  README and the runtime section of `docs/operations.md` now say that the
+  generator and the migrations start no role, so an application that serves
+  web requests alone leaves the message ready until
+  `bundle exec solid_objects start` runs the roles. The message is durable
+  and waits; it is not lost. `test/integration/background_pickup_test.rb`
+  pins it: the message reads `ready` and the actor state stays empty until a
+  worker runs. This matches solid-objects-js#22, which reported the same gap
+  for `runtime.run(signal)` in the Node package.
+
 - Add `examples/at_least_once` and `bundle exec rake at_least_once`, an
   executable proof that the at-least-once clause fires and that the
   documented remedy absorbs it. One actor turn stages an effect that writes

README.md

@@ -662,6 +662,12 @@ message = order.async(
 ).submit
 ```
 
+`async` needs a running actor worker. Installing the engine and migrating the
+schema starts no role, so a process that only serves web requests leaves the
+message ready. Nothing is lost. The message waits until
+`bundle exec solid_objects start` runs the roles. See
+[Worker requirements](#worker-requirements) for the feature-by-role table.
+
 Use `available_at:` to spread bulk work or delay one message:
 
 ```ruby

docs/operations.md

@@ -31,6 +31,13 @@ Start all configured roles:
 bundle exec solid_objects start
 ```
 
+The generator and the migrations prepare the database and start nothing. A
+process claims ready messages only after this command starts its roles, so an
+application that serves web requests alone leaves every `async` message ready.
+The message is durable and waits for the first process that runs the roles. A
+direct call or an explicit `sync` needs no running role, because the caller's
+own path executes it.
+
 The command loads the host application's `app/actors` directories before
 starting any runtime role, even when Rails eager loading is disabled. Actors in
 the conventional directory do not need initializer references. The targeted

test/integration/background_pickup_test.rb

@@ -0,0 +1,37 @@
+# frozen_string_literal: true
+
+require "database_test_helper"
+
+class BackgroundPickupTest < ActiveSupport::TestCase
+  class MailboxActor < SolidObjects::Actor
+    actor_type "background-pickup-mailbox"
+
+    attribute :delivered, default: 0
+
+    def receive
+      self.delivered += 1
+    end
+  end
+
+  test "leaves an async message ready until a worker runs the roles" do
+    message = MailboxActor.ref("inbox").async.receive
+
+    assert_equal "ready", message.status
+    assert_empty SolidObjects::Instance.find_by!(
+      actor_type: "background-pickup-mailbox", actor_id: "inbox"
+    ).state
+
+    worker = SolidObjects::Worker.new
+    begin
+      worker.run_until_idle
+    ensure
+      worker.stop
+    end
+
+    assert_equal "completed", message.status
+    assert_equal(
+      { "delivered" => 1 },
+      SolidObjects::Instance.find_by!(actor_type: "background-pickup-mailbox", actor_id: "inbox").state
+    )
+  end
+end