I'm not sure whether a simple truthiness check makes sense here. Sure, if the user highlights the entire path and then deletes it, this'll work. More likely however (especially considering virtual keyboards, e.g. on the Deck), they're gonna backspace one-by-one, causing a restore operation to just re-insert the /. This of course won't work as a prefix path either

The easiest way to resolve this would be to not store the "last valid" value at all, instead just restoring it to the same path a new install would use:

Sorry if this is a silly question but I don't see where to find the original defaultWinePrefix? In the code you linked the suggestedWinePrefix is built partly the title or appName from WineSelector's props, which we don't have in the component we're working on... Is there something like a constants file that the initial value comes from?

Instead of storing lastValidPrefix (which the name can be a bit misleading, it doesn't mean this is valid) I imagine this logic for handlePathChange:

function handlePathChange(newPath: string) {
  if (newPath) {
    // not empty, all good
    setDefaultWinePrefix(newPath)
  }  else {
    // empty, show an alert/warning saying it will be reverted to the previous value
    // reset the value to the original config value
  }
}

But I actually think we have a problem with the PathSelectionBox component because we have no simple way of resetting the value (we would have to re-render the component cause it uses the internal tmpPath state).

I imagine the onPathChange function that we pass with the props could be updated to return a string (instead of void) that the component should set the field to, and instead of simply calling that function in the onBlur callback, we could wrap it to call it and use the return value to update with setTmpPath(theReturnValueOfOnPathChange).