[Rails] Explain how to render without a view context

reference/rails/rendering-out-of-context.md

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+Most Rails renders are synchronous responses to user requests. In these synchronous contexts, the `render` method is defined and an `ActionView::Context` is present. We need these two things to render Phlex components.
+
+However, these two things are not always present. How can we render Phlex components in an ActiveRecord callback? How can we render in a background job? The answer is to use `ApplicationController.render_to_string`.
+
+Example 1: rendering a Phlex component for a Turbo Stream in response to an ActiveRecord callback:
+
+```
+class Post < ApplicationRecord
+  after_create_commit {
+    model = self
+    component = Components::MyPostComponent.new(post: model)
+    # Setting the request is not always required, but common Rails features
+    # including path helpers fail without it.
+    fake_rack_request = Rack::MockRequest.env_for("http://localhost", method: :get)
+    controller.request = ActionDispatch::Request.new(fake_rack_request)
+    html = controller.render_to_string(component, layout: false)
+    broadcast_prepend_to("my-streamable", html:)
+  }
+end
+```
+
+Example 2: rendering a Phlex component in a background job:
+```
+class MailJob < ApplicationJob
+  queue_as :default
+
+  def perform(*args)
+    model = Post.create!
+    component = Components::MyPostComponent.new(post: model)
+    fake_rack_request = Rack::MockRequest.env_for("http://localhost", method: :get)
+    controller.request = ActionDispatch::Request.new(fake_rack_request)
+    html = controller.render_to_string(component, layout: false)
+    HelloMailer.with(html:).hello_email.deliver_now
+  end
+end
+```