Cast `annotation.id` to a string in a few places

The `id` property only exists once an annotation has been saved. Add
casts in a few places where we know that this is the case.

src/sidebar/components/annotation-header.js

@@ -58,7 +58,10 @@ export default function AnnotationHeader({
   const showReplyButton = replyCount > 0 && isCollapsedReply;
   const showExtendedInfo = !isReply(annotation);
 
-  const onReplyCountClick = () => setExpanded(annotation.id, true);
+  const onReplyCountClick = () =>
+    // If an annotation has replies it must have been saved and therefore have
+    // an ID.
+    setExpanded(/** @type {string} */ (annotation.id), true);
 
   return (
     <header className="annotation-header">

src/sidebar/components/annotation.js

@@ -105,7 +105,10 @@ function Annotation({
     }
   };
 
-  const onToggleReplies = () => setExpanded(annotation.id, !!threadIsCollapsed);
+  const onToggleReplies = () =>
+    // nb. We assume the annotation has an ID here because it is not possible
+    // to create replies until the annotation has been saved.
+    setExpanded(/** @type {string} */ (annotation.id), !!threadIsCollapsed);
 
   return (
     /* eslint-disable-next-line jsx-a11y/no-noninteractive-element-interactions */

src/sidebar/store/modules/real-time-updates.js

@@ -102,12 +102,13 @@ function receiveRealTimeUpdates({
         ann.group === groups.selectors.focusedGroupId(getState()) ||
         route.selectors.route(getState()) !== 'sidebar'
       ) {
-        pendingUpdates[ann.id] = ann;
+        pendingUpdates[/** @type {string} */ (ann.id)] = ann;
       }
     });
     deletedAnnotations.forEach(ann => {
+      const id = /** @type {string} */ (ann.id);
       // Discard any pending but not-yet-applied updates for this annotation
-      delete pendingUpdates[ann.id];
+      delete pendingUpdates[id];
 
       // If we already have this annotation loaded, then record a pending
       // deletion. We do not check the group of the annotation here because a)
@@ -115,8 +116,8 @@ function receiveRealTimeUpdates({
       // even if the annotation is from the current group, it might be for a
       // new annotation (saved in pendingUpdates and removed above), that has
       // not yet been loaded.
-      if (annotations.selectors.annotationExists(getState(), ann.id)) {
-        pendingDeletions[ann.id] = true;
+      if (annotations.selectors.annotationExists(getState(), id)) {
+        pendingDeletions[id] = true;
       }
     });
     dispatch({

src/sidebar/util/view-filter.js

@@ -191,5 +191,5 @@ export default function filterAnnotations(annotations, filters) {
     .filter(ann => {
       return ann.id && rootFilter.matches(ann);
     })
-    .map(ann => ann.id);
+    .map(ann => /** @type {string} */ (ann.id));
 }