bug: ordered_icons compares nil when marker conversion fails

Bắt đầu tại lua/render-markdown/settings.lua, ở callback mặc định bullet.ordered_icons, và chạy bản tái hiện Neovim headless được cung cấp. Thêm coverage hồi quy cho các giá trị marker rỗng và không phải số, đồng thời giữ nguyên hành vi đánh số hợp lệ; hoàn thành khi callback không còn phát sinh lỗi và các trường hợp hợp lệ hiện có vẫn không thay đổi.

Neovim version

NVIM v0.12.5 (LuaJIT 2.1.1788856981)

Neovim distribution / OS / terminal

LazyVim on macOS. The deterministic reproduction below uses headless Neovim; the terminal for the original editing error was not recorded.

Describe the bug

The default bullet.ordered_icons callback calls tonumber(...), then compares the result with 1 without checking for nil. If the supplied marker text cannot be converted to a number, rendering aborts with:

Error msg_show.lua_error vim.schedule callback:
.../render-markdown.nvim/lua/render-markdown/settings.lua:164: attempt to compare number with nil
stack traceback:
  .../settings.lua:164: in function 'get_string'
  .../render/markdown/bullet.lua:44: in function 'setup'
  .../render/base.lua:20: in function 'execute'
  .../render/markdown/list.lua:18: in function 'run'
  .../render/base.lua:21: in function 'execute'
  .../handler/markdown.lua:58: in function 'callback'
  .../request/view.lua:76: in function 'callback'
  .../request/view.lua:88: in function 'query'
  .../request/view.lua:71: in function 'nodes'
  .../handler/markdown.lua:55: in function 'parse'
  .../core/handlers.lua:94: in function 'tree'
  .../core/handlers.lua:51: in function 'run'
  .../core/ui.lua:156: in function 'callback'

This was reported during a real editing session on 8.14.0 (640a3ec6d538bad17c328be373c7cad0293d9589). I have verified the unsafe conversion/comparison, but have not captured the original marker text or reproduced the sequence of editing/parser events that supplied it. An incomplete or stale marker is a hypothesis, not an established cause.

Deterministic callback reproduction

With the plugin on runtimepath, execute:

local ordered_icons = require('render-markdown.settings').bullet.default.ordered_icons
ordered_icons({ level = 1, index = 3, value = '' })

This raises the exact settings.lua:164 comparison error. value = '.', ')', or 'abc' also reproduces it. These are injected callback inputs, not a claim that standalone malformed Markdown necessarily produces an ordered-list parser node.

For example, with a fresh checkout:

nvim --headless -u NONE -i NONE \
  --cmd 'set rtp+=/path/to/render-markdown.nvim' \
  -c 'lua local f = require("render-markdown.settings").bullet.default.ordered_icons; local ok, result = pcall(f, { level = 1, index = 3, value = "" }); print(ok, result)' \
  -c qa

Observed: false .../settings.lua:164: attempt to compare number with nil.

Expected behavior / proposed fix

A failed marker conversion should not abort rendering. Guard the comparison and reuse the callback's existing item-index fallback:

return ('%d.'):format(index and index > 1 and index or ctx.index)

Verified in headless Neovim: valid explicit markers greater than one retain their number; markers starting at zero or one retain the existing item-position numbering; unconvertible marker strings fall back to ctx.index without crashing. A regression test fails before this guard and passes afterward.

Plugin configuration at the time of the error

Custom overrides for this plugin (remaining options inherited from LazyVim):

opts = {
    latex = { block = false },
    anti_conceal = { ignore = { virtual_lines = false } },
}

There was no custom bullet.ordered_icons callback. A local override using the proposed guard is now in place.

Healthcheck output

Collected headlessly with the above overrides and installed parser/icon dependencies in an isolated checkout. This is a minimal configuration healthcheck, not a capture of the original live editor session:

==============================================================================
render-markdown:                                                            ✅

render-markdown.nvim [versions] ~
- ✅ OK neovim >= 0.11
- ✅ OK tree-sitter ABI: 15
- ✅ OK plugin: 8.14.0

render-markdown.nvim [configuration] ~
- ✅ OK valid

render-markdown.nvim [tree-sitter markdown] ~
- ✅ OK parser: installed
- ✅ OK ABI: 15
- ✅ OK highlights: ~/.local/share/nvim/site/queries/markdown/highlights.scm
- ✅ OK highlighter: enabled

render-markdown.nvim [tree-sitter markdown_inline] ~
- ✅ OK parser: installed
- ✅ OK ABI: 15
- ✅ OK highlights: ~/.local/share/nvim/site/queries/markdown_inline/highlights.scm

render-markdown.nvim [tree-sitter html] ~
- ✅ OK parser: installed
- ✅ OK ABI: 14

render-markdown.nvim [tree-sitter latex] ~
- ✅ OK parser: installed
- ✅ OK ABI: 15

render-markdown.nvim [tree-sitter yaml] ~
- ✅ OK parser: installed
- ✅ OK ABI: 15

render-markdown.nvim [icons] ~
- ✅ OK using: mini.icons

render-markdown.nvim [latex] ~
- ✅ OK using: { "utftex", "latex2text" }

render-markdown.nvim [conflicts] ~
- ✅ OK headlines: not installed
- ✅ OK markview: not installed
- ✅ OK obsidian: not installed
- ✅ OK snacks: not installed

Plugin error log

The original scheduled-callback traceback is included above; a separate plugin error-log capture is unavailable.

Additional verification

A fresh checkout of current main has the same default callback and commit as the installed 8.14.0 version. The callback reproduction does not require a Tree-sitter parser, so parsers were not updated as part of this diagnosis. This differs from #504, which involved the pre-8.0 callback signature in user configuration.