fix: hide ThreadIndicator badge inside ThreadDrawer compose box

Inside the ThreadDrawer the user is already in thread context, so showing
the "Thread" badge in the reply chip is redundant and visually noisy.

The compose box always sets replyDraft.relation.rel_type = RelationType.Thread
when threadRootId is set (so the message goes to the right thread), but that
should not make the ThreadIndicator visible there.

Add !threadRootId guard to the ThreadIndicator render condition.

Adds 4 unit tests covering the four branches of the condition.

Author: Evie Gauthier

src/app/components/message/ThreadIndicator.test.tsx

@@ -0,0 +1,43 @@
+/**
+ * Tests for the ThreadIndicator visibility condition in the compose strip.
+ *
+ * The indicator renders when a user is replying to a thread message from the
+ * main timeline (no threadRootId). It must NOT appear when composing inside
+ * the ThreadDrawer (threadRootId is set), because the drawer already makes the
+ * thread context obvious.
+ *
+ * Mirrors the exact render guard in RoomInput.tsx:
+ *   {replyDraft.relation?.rel_type === RelationType.Thread && !threadRootId && (
+ *     <ThreadIndicator />
+ *   )}
+ */
+import { describe, it, expect } from 'vitest';
+import { render, screen } from '@testing-library/react';
+import { RelationType } from '$types/matrix-sdk';
+import { ThreadIndicator } from './Reply';
+
+function Subject({ relType, threadRootId }: { relType?: string; threadRootId?: string }) {
+  return <>{relType === RelationType.Thread && !threadRootId && <ThreadIndicator />}</>;
+}
+
+describe('ThreadIndicator visibility in compose strip', () => {
+  it('renders in the main timeline compose box when a thread relation is active', () => {
+    render(<Subject relType={RelationType.Thread} />);
+    expect(screen.getByText('Thread')).toBeInTheDocument();
+  });
+
+  it('is hidden inside the ThreadDrawer when threadRootId is set', () => {
+    render(<Subject relType={RelationType.Thread} threadRootId="$root:example.com" />);
+    expect(screen.queryByText('Thread')).not.toBeInTheDocument();
+  });
+
+  it('is hidden when the draft has no relation', () => {
+    render(<Subject relType={undefined} />);
+    expect(screen.queryByText('Thread')).not.toBeInTheDocument();
+  });
+
+  it('is hidden for a non-thread relation type', () => {
+    render(<Subject relType="m.in_reply_to" />);
+    expect(screen.queryByText('Thread')).not.toBeInTheDocument();
+  });
+});

src/app/features/room/RoomInput.tsx

@@ -1126,7 +1126,7 @@ export const RoomInput = forwardRef<HTMLDivElement, RoomInputProps>(
                         grow="Yes"
                         style={{ minWidth: 0 }}
                       >
-                        {replyDraft.relation?.rel_type === RelationType.Thread && (
+                        {replyDraft.relation?.rel_type === RelationType.Thread && !threadRootId && (
                           <ThreadIndicator />
                         )}
                         <ReplyLayout