Including a test harness for it, and making sure the cursor is always at the end.

packages/cli/package.json

@@ -8,6 +8,7 @@
     "build": "tsc && touch dist/.last_build",
     "start": "node dist/gemini.js",
     "debug": "node --inspect-brk dist/gemini.js",
+    "test": "vitest run",
     "lint": "eslint . --ext .ts,.tsx",
     "format": "prettier --write ."
   },
@@ -32,6 +33,7 @@
     "@types/node": "^20.11.24",
     "@types/react": "^19.1.0",
     "@types/yargs": "^17.0.32",
+    "jsdom": "^26.1.0",
     "typescript": "^5.3.3"
   },
   "engines": {