Can't find rule grammarSpec or tree structure error while using direct left recursion

A simple term rule:

```
term[int priority]
: simpleTerm
| term[$priority - 1]
;
```

will throw cannot find rule grammarSpec error. Removing the direct left recursion removes the error.

Start by reproducing the grammar shown in the issue and capture the full “cannot find rule grammarSpec” or tree-structure error. Trace how ANTLR handles direct left recursion with the parameterized term rule; done means the grammar is processed without that error and the existing behavior remains valid.

Written by the indexing model from the issue text.