fix(tui): chunked large transcript rebuilds

Replayed idle transcripts in bounded message and time chunks, painting cleared scrollback between macrotasks so terminal input remains responsive during restore and tree navigation. Kept streaming rebuilds atomic and migrated every rebuild caller to await completion.

Fixes #8133

packages/coding-agent/src/modes/controllers/command-controller.ts

@@ -1422,7 +1422,7 @@ export class CommandController {
 
 			// Rebuild chat from the new session (which now contains the handoff document).
 			this.ctx.clearTransientSessionUi();
-			this.ctx.renderInitialMessages();
+			await this.ctx.renderInitialMessages();
 			this.ctx.statusLine.invalidate();
 			this.ctx.updateEditorBorderColor();
 			await this.ctx.reloadTodos();