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

Enable EmmyLua's assign-type-mismatch diagnostic after correcting the
runtime annotations and assignments it flags.

Correct option, tuple, and return types, and use separate locals when a
value changes representation. Add guards and narrow casts where needed
so the runtime passes the stricter check. Regenerate the affected docs.

AI-assisted

Enable EmmyLua's need-check-nil diagnostic and resolve nullable values
through more precise types, explicit invariants, and guards for missing
runtime state. Keep analyzer-specific workarounds local and update the
affected API documentation.

Exclude the bundled re.lua from analysis so its nil-check warnings do
not fail CI.

AI-assisted

- call-non-callable
- missing-fields
- redefined-label
- redefined-local
- undefined-field
- unreachable-code

Promote redefined-local and unreachable-code to warnings.

Fix DOS line-ending handling for multiline semantic tokens, and support
intersection types in the help parser.

AI-assisted

Problem:
TSHighlighter._on_conceal_line() parses with the range { row, row }. A
Range2 has an exclusive end, so that is the empty range, and no injected
region ever intercepts it.

The root tree is parsed regardless, because its region is empty, so only
injections are affected: conceal_lines metadata coming from an injected
language's highlights query is dropped. on_range_impl() then records the
row in _conceal_checked, so the miss persists until the buffer changes.

For a markdown code block nested in a markdown code block, the inner
fence delimiters stay visible and nvim_win_text_height() reports 5 rows
where 3 are displayed.

Solution:
Pass the one-row range, as the on_range_impl() call below already does.

AI-assisted

Problem:
Calling vim.treesitter.start() a second time on a buffer that already
has an active TSHighlighter creates a brand new instance instead of
reusing it, whether the parser tree is unchanged (e.g. calling start()
twice) or different (e.g. switching languages). Either way the old
instance is silently discarded without calling :destroy() on it, so
its on_bytes/on_changedtree/on_detach callbacks stay registered and
its buffer-local state (spelloptions, decoration namespace) is never
restored, both leaking indefinitely for an orphaned instance that
nothing references anymore.

Solution:
Return the existing instance when TSHighlighter.active[source] is
already set for the same parser tree, instead of unconditionally
constructing a new one. When the tree differs instead (e.g. a language
switch), destroy() the old instance first, matching stop() semantics,
before constructing the new one.

Problem: `nvim_exec_autocmds({ buf = ... })` matches the target buffer, but callbacks and modelines run with the caller buffer current rather than the target buffer.

Solution: Execute the buffered path in prepared target-buffer context and restore the caller afterward.

Problem:
Cannot remove a `@conceal` highlight when defined in highlights.scm.

Solution:
Support a `@noconceal` highlight that works similarly to `@nospell` where it
overrides the conceal set on the range to remove it. Additionally, can
set the conceal metadata field to false for the same behavior.