Make event loops 1:1 with agents

Event loops ought to be 1:1 with agents, let's make it so.

Helps with #4198.

source

@@ -77492,11 +77492,6 @@ console.assert(iframeWindow.frameElement === null);
   any other group. Each such group is a <dfn data-export="">unit of related similar-origin browsing
   contexts</dfn>.</p>
 
-  <p class="note">There is also at most one <span>event loop</span> per <span>unit of related
-  similar-origin browsing contexts</span> (though several <span data-x="unit of related
-  similar-origin browsing contexts">units of related similar-origin browsing contexts</span> can
-  have a shared <span>event loop</span>).</p>
-
   </div>
 
 
@@ -78978,13 +78973,9 @@ interface <dfn>BarProp</dfn> {
      </dd>
 
      <dt>The <span>responsible event loop</span></dt>
-     <dd>
-
-      <p>Return the <span>event loop</span> that is associated with the <span>unit of related
-      similar-origin browsing contexts</span> to which <var>window</var>'s <span>browsing
-      context</span> belongs.</p>
-
-     </dd>
+     <dd><p>Return the <span>event loop</span> associated with the <span>agent</span> whose set of
+     <span data-x="JavaScript realm">realms</span> contains <var>window</var>'s <span>relevant
+     Realm</span>.</p></dd>
 
      <dt>The <span>responsible document</span></dt>
      <dd>
@@ -88680,7 +88671,7 @@ import "https://example.com/foo/../module2.mjs";</code></pre>
   <p class="&#x0058;&#x0058;&#x0058;">JavaScript is expected to define <span
   data-x="agent">agents</span> in more detail; in particular that they hold a set of <span
   data-x="concept-global-object-realm">realms</span>: <a
-  href="https://github.com/tc39/ecma262/issues/882">tc39/ecma262 issue #882</a>.</p>
+  href="https://github.com/tc39/ecma262/issues/1357">tc39/ecma262 issue #1357</a>.</p>
 
   <p class="note">Conceptually, the <span>agent</span> concept is an architecture-independent,
   idealized "thread" in which JavaScript code runs. Such code can involve multiple globals/<span
@@ -89119,27 +89110,11 @@ dictionary <dfn>PromiseRejectionEventInit</dfn> : <span>EventInit</span> {
 
   <p>To coordinate events, user interaction, scripts, rendering, networking, and so forth, user
   agents must use <dfn data-x="event loop" data-lt="event loop" data-export="">event loops</dfn> as
-  described in this section. There are two kinds of event loops: those for <span
-  data-x="browsing context">browsing contexts</span>, and those for <a
-  href="#workers">workers</a>.</p>
+  described in this section. Each <span>agent</span> has one <span>event loop</span>.
 
-  <p>There must be at least one <span>browsing context</span> <span>event loop</span> per user
-  agent, and at most one per <span>unit of related similar-origin browsing contexts</span>.</p>
-
-  <p class="note">When there is more than one <span>event loop</span> for a <span>unit of related
-  browsing contexts</span>, complications arise when a <span>browsing context</span> in that group
-  is <span data-x="navigate">navigated</span> such that it switches from one <span>unit of related
-  similar-origin browsing contexts</span> to another. This specification does not currently describe
-  how to handle these complications.</p>
-
-  <p>A <span>browsing context</span> <span>event loop</span> always has at least one <span>browsing
-  context</span>. If such an <span>event loop</span>'s <span data-x="browsing context">browsing
-  contexts</span> all go away, then the <span>event loop</span> goes away as well. A <span>browsing
-  context</span> always has an <span>event loop</span> coordinating its activities.</p>
-
-  <p><a href="#worker-event-loop">Worker event loops</a> are simpler: each worker has one
-  <span>event loop</span>, and the <span data-x="run a worker">worker processing model</span>
-  manages the <span>event loop</span>'s lifetime.</p>
+  <p class="note">This specification does not currently describe how to handle the complications
+  arising from <span data-x="navigate">navigating</span> between <span data-x="similar-origin window
+  agent">similar-origin window agents</span>.</p>
 
   <hr>
 
@@ -89187,26 +89162,27 @@ dictionary <dfn>PromiseRejectionEventInit</dfn> : <span>EventInit</span> {
 
   </dl>
 
-  <p>Each <span data-x="concept-task">task</span> in a <span>browsing context</span> <span>event
-  loop</span> is associated with a <code>Document</code>; if the task was queued in the context of
-  an element, then it is the element's <span>node document</span>; if the task was queued in the context
-  of a <span>browsing context</span>, then it is the <span>browsing context</span>'s <span>active
-  document</span> at the time the task was queued; if the task was queued by or for a <span
-  data-x="concept-script">script</span> then the document is the <span>responsible document</span>
-  specified by the script's <span>settings object</span>.</p>
+  <p>Each <span data-x="concept-task">task</span> in an <span>event loop</span> for a
+  <span>similar-origin window agent</span> is associated with a <code>Document</code>; if the task
+  was queued in the context of an element, then it is the element's <span>node document</span>; if
+  the task was queued in the context of a <span>browsing context</span>, then it is the
+  <span>browsing context</span>'s <span>active document</span> at the time the task was queued; if
+  the task was queued by or for a <span data-x="concept-script">script</span> then the document is
+  the <span>responsible document</span> specified by the script's <span>settings object</span>.</p>
 
   <p>A <span data-x="concept-task">task</span> is intended for a specific <span>event loop</span>:
   the <span>event loop</span> that is handling <span data-x="concept-task">tasks</span> for the
   <span data-x="concept-task">task</span>'s associated <code>Document</code> or <a
   href="#workers">worker</a>.</p>
+  <!-- TODO: worklets? -->
 
   <p>When a user agent is to <dfn data-export="">queue a task</dfn>, it must add the given task to
   one of the <span data-x="task queue">task queues</span> of the relevant <span>event
   loop</span>.</p>
 
   <p>Each <span data-x="concept-task">task</span> is defined as coming from a specific <dfn
   data-export="">task source</dfn>. All the tasks from one particular <span>task source</span> and
-  destined to a particular <span>event loop</span> (e.g. the callbacks generated by timers of a
+  destined to a particular <span>event loop</span> (e.g., the callbacks generated by timers of a
   <code>Document</code>, the events fired for mouse movements over that <code>Document</code>, the
   tasks queued for the parser of that <code>Document</code>) must always be added to the same
   <span>task queue</span>, but <span data-x="concept-task">tasks</span> from different <span
@@ -89241,10 +89217,10 @@ dictionary <dfn>PromiseRejectionEventInit</dfn> : <span>EventInit</span> {
    <!-- lots of places in the spec refer to "step 1" -->
    <li id="step1"><p>Let <var>oldestTask</var> be the oldest <span data-x="concept-task">task</span>
    on one of the <span>event loop</span>'s <span data-x="task queue">task queues</span>, if any,
-   ignoring, in the case of a <span>browsing context</span> <span>event loop</span>, tasks whose
-   associated <code>Document</code>s are not <span>fully active</span>. The user agent may pick any
-   <span>task queue</span>. If there is no task to select, then jump to the <i>microtasks</i> step
-   below.</p></li>
+   ignoring, in the case of a <span>similar-origin window agent</span> <span>event loop</span>,
+   tasks whose associated <code>Document</code>s are not <span>fully active</span>. The user agent
+   may pick any <span>task queue</span>. If there is no task to select, then jump to the
+   <i>microtasks</i> step below.</p></li>
 
    <li>
     <p>Report the duration of time during which the user agent does not execute this loop by
@@ -89296,9 +89272,8 @@ dictionary <dfn>PromiseRejectionEventInit</dfn> : <span>EventInit</span> {
    </li>
 
    <li>
-    <p><dfn data-export="">Update the rendering</dfn>: If this <span>event loop</span> is a
-    <span>browsing context</span> <span>event loop</span> (as opposed to a <a
-    href="#workers">worker</a> <span>event loop</span>), then run the following substeps.</p>
+    <p><dfn data-export="">Update the rendering</dfn>: if this <span>event loop</span> is for a
+    <span>similar-origin window agent</span>, then:</p>
 
     <ol>
      <li>
@@ -89422,14 +89397,13 @@ dictionary <dfn>PromiseRejectionEventInit</dfn> : <span>EventInit</span> {
     </ol>
    </li>
 
-   <li><p>If this is a <span>browsing context</span> <span>event loop</span> (as opposed to a <a
-   href="#workers">worker</a> <span>event loop</span>), and there are no <span
-   data-x="concept-task">tasks</span> in the <span>event loop</span>'s <span data-x="task
-   queue">task queues</span>, and the <span>event loop</span>'s <span>microtask queue</span> is
-   empty, and none of the <span data-x="browsing context">browsing contexts</span> have a
-   <span>rendering opportunity</span>, then for each <span>browsing context</span>, run the steps in
-   the <span>start an idle period algorithm</span>, passing the <code>Window</code> associated with
-   that <span>browsing context</span>. <ref spec="REQUESTIDLECALLBACK"></p></li>
+   <li><p>If this is an <span>event loop</span> for a <span>similar-origin window agent</span>, and
+   there are no <span data-x="concept-task">tasks</span> in the <span>event loop</span>'s <span
+   data-x="task queue">task queues</span>, and the <span>event loop</span>'s <span>microtask
+   queue</span> is empty, and none of the <span data-x="browsing context">browsing contexts</span>
+   have a <span>rendering opportunity</span>, then for each <span>browsing context</span>, run the
+   steps in the <span>start an idle period algorithm</span>, passing the <code>Window</code>
+   associated with that <span>browsing context</span>. <ref spec="REQUESTIDLECALLBACK"></p></li>
 
    <li>
     <p>Report the duration of the <span>update the rendering</span> step by performing the
@@ -89450,14 +89424,16 @@ dictionary <dfn>PromiseRejectionEventInit</dfn> : <span>EventInit</span> {
    </li>
 
    <li>
-    <p>If this is a <a href="#workers">worker</a> <span>event loop</span> (i.e., one running for
-    a <code>WorkerGlobalScope</code>):</p>
+    <p>If this is an <span>event loop</span> that is not for a <span>similar-origin window
+    agent</span> or <span>worklet agent</span> (e.g., one for a <span>dedicated worker
+    agent</span>):</p>
 
     <ol>
      <li>
       <p>If this is a <span data-x="concept-AnimationFrameProvider-supported">supported</span>
       <code>DedicatedWorkerGlobalScope</code> and the user agent believes that it would benefit from
       having its rendering updated at this time, then:</p>
+      <!-- TODO: do we need to grab this global from the agent now? -->
 
       <ol>
        <li><p>Let <var>now</var> be the <span>current high resolution time</span>. <ref
@@ -97890,6 +97866,9 @@ interface <dfn>SharedWorkerGlobalScope</dfn> : <span>WorkerGlobalScope</span> {
 
   <h4 id="worker-event-loop">The event loop</h4>
 
+  <!-- TODO: should we create an "agent mixin" for workers that we can use here? Should "closing"
+       move there? -->
+
   <p>Each <code>WorkerGlobalScope</code> object has a distinct <span>event loop</span>, separate
   from those used by <span data-x="unit of related similar-origin browsing contexts">units of related
   similar-origin browsing contexts</span>. This <span>event loop</span> has no associated