Expand/Shrink Selection stops working inside of fenced divs (:::).

Bug description

Expand Selection (editor.action.smartSelect.expand) and Shrink Selection (editor.action.smartSelect.expand) stops working correctly if the R code chunk is inside a fenced div. It expands to select everything or select none.

Steps to reproduce

Following R code cell is an example where this behavior occurs. Expand Selection doesn't expand to brackets or line, it expands to all in the cell.

::: {.callout-note collapse="true"}
```{r}
library(stringr)

options(
  max.print = 200
)
```
:::

### Actual behavior

_No response_

### Expected behavior

_No response_

### Your environment

_No response_

Start by reproducing the provided R code chunk inside the fenced div and compare Expand Selection and Shrink Selection behavior with the same chunk outside it. Trace how fenced-div boundaries affect selection handling; done means expansion reaches brackets and lines normally instead of selecting the entire cell or nothing.