Problem: Argument type mismatches are excluded from EmmyLua checks.

Solution: Correct runtime annotations and calls, document local checker
workarounds, and enable the diagnostic.

AI-assisted

Problem:
Tree-sitter uses UINT32_MAX for full-document ranges, which becomes -1 on 32-bit platforms and reaches _foldupdate as an invalid end row.

Solution:
Treat negative changed-range end rows as unbounded and clamp them to the buffer line count. Add a regression test that simulates the 32-bit sentinel.

AI-assisted: Codex

Problem:
`nvim_create_autocmd` is too verbose and its `callback` requires extra
"nesting".

Solution:
Introduce `nvim_on`. Start using it internally. Then we can get a feel
for how it should look before making it public.

Allow `bufnr` as a positional param name because it is very common.
However as a field name, or part of a function name, it is usually
a mistake.

Problem:
`:help dev-name-common` states that "buf" should be used instead of
"buffer" but there are cases where buffer is mentioned in the lua API.

Solution:
- Rename occurrences of "buffer" to "buf" for consistency with the
  documentation.
- Support (but deprecate) "buffer" for backwards compatibility.

Co-authored-by: Justin M. Keyes <justinkz@gmail.com>

Problem:

The fold refresh path for foldminlines/foldnestmax creates a new
FoldInfo and starts an async parse. If FileType or BufUnload re-enters
before that callback returns, foldinfos[bufnr] can be cleared or
replaced. The callback then indexes a stale slot and raises an "attempt
to index a nil value" error.

Solution:

Capture the FoldInfo created for the refresh and carry that object
through the async callback. Before calling foldupdate(), verify that the
buffer still points at the same FoldInfo generation; otherwise ignore
the stale callback.

AI-assisted: Codex

Fixes #38461

Problem:
VimEnter clears foldinfo, so register_cbs is called again after
VimEnter. The duplicate parser callbacks break incremental fold
computation.

Solution:
Check if the callbacks are already registered.