docs: Use Array.prototype.at(index) instead of out-of-bounds accesses

AGENTS.md

@@ -87,6 +87,7 @@ Examples: `fix(tui): simplify thinking toggle styling`, `docs: update contributi
 
 - Keep things in one function unless composable or reusable
 - Avoid unnecessary destructuring. Instead of `const { a, b } = obj`, use `obj.a` and `obj.b` to preserve context
+- Avoid possibly out-of-bounds array access. Instead of `array[index] ?? {}`, use `array.at(index) ?? {}`. Instead of `array[array.length - 1]`, use `array.at(-1)`
 - Avoid `try`/`catch` where possible
 - Avoid using the `any` type
 - Prefer single word variable names where possible