Change CIDER state persistence key to cater for threads

Extending the CIDER state persistence to threads and make sure that SendMessageComposer can restore drafts for specific threads

This also prevents the thread's replyToEvent to leaking in the room composer

src/components/views/rooms/SendMessageComposer.tsx

@@ -164,6 +164,20 @@ export default class SendMessageComposer extends React.Component<IProps> {
         window.addEventListener("beforeunload", this.saveStoredEditorState);
     }
 
+    public componentDidUpdate(prevProps: IProps): void {
+        const replyToEventChanged = this.props.replyToEvent !== prevProps.replyToEvent;
+        if (replyToEventChanged) {
+            this.model.reset([]);
+        }
+
+        if (this.props.replyInThread && this.props.replyToEvent && (!prevProps.replyToEvent || replyToEventChanged)) {
+            const partCreator = new CommandPartCreator(this.props.room, this.context);
+            const parts = this.restoreStoredEditorState(partCreator) || [];
+            this.model.reset(parts);
+            this.editorRef.current?.focus();
+        }
+    }
+
     private onKeyDown = (event: KeyboardEvent): void => {
         // ignore any keypress while doing IME compositions
         if (this.editorRef.current?.isComposing(event)) {
@@ -484,7 +498,12 @@ export default class SendMessageComposer extends React.Component<IProps> {
     }
 
     private get editorStateKey() {
-        return `mx_cider_state_${this.props.room.roomId}`;
+        let key = `mx_cider_state_${this.props.room.roomId}`;
+        const thread = this.props.replyToEvent?.getThread();
+        if (thread) {
+            key += `_${thread.id}`;
+        }
+        return key;
     }
 
     private clearStoredEditorState(): void {
@@ -492,6 +511,10 @@ export default class SendMessageComposer extends React.Component<IProps> {
     }
 
     private restoreStoredEditorState(partCreator: PartCreator): Part[] {
+        if (this.props.replyInThread && !this.props.replyToEvent) {
+            return null;
+        }
+
         const json = localStorage.getItem(this.editorStateKey);
         if (json) {
             try {