test(config): cover link_severity in parity harnesses and docs

Both editor harnesses now emit diagnostic.link_severity and exercise a
non-default override ('error') in the sample scenario, diffed against the
shared golden. Drop the README "not wired" caveat now that the value flows
through, and document the g:nuwiki_link_severity global.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

README.md

@@ -255,6 +255,7 @@ plugin:
 let g:nuwiki_wiki_root            = '~/vimwiki'
 let g:nuwiki_file_extension       = '.wiki'
 let g:nuwiki_log_level            = 'warn'
+let g:nuwiki_link_severity        = 'warn' " 'off'|'hint'|'warn'|'error'
 let g:nuwiki_no_default_mappings  = 0   " set to 1 to skip the keymap layer
 let g:nuwiki_no_folding           = 0   " set to 1 to skip foldexpr setup
 let g:nuwiki_mouse_mappings       = 0   " set to 1 to enable mouse maps
@@ -273,7 +274,7 @@ let g:nuwiki_mouse_mappings       = 0   " set to 1 to enable mouse maps
 | `folding` | string | `'lsp'` | `'lsp'` \| `'expr'` \| `'off'` |
 | `wikis` | list of tables | `nil` | per-wiki tables (see below); wins over the single-wiki shorthand |
 | `mappings` | table | all on | keymap subgroups (see below) |
-| `diagnostic` | table | — | `{ link_severity = … }` (see note below) |
+| `diagnostic` | table | `{ link_severity = 'warn' }` | `link_severity`: `'off'` \| `'hint'` \| `'warn'` \| `'error'` |
 
 #### `mappings` subgroups
 
@@ -340,15 +341,11 @@ For users configuring without Lua.
 | `g:nuwiki_wiki_root` | `'~/vimwiki'` | single-wiki root |
 | `g:nuwiki_file_extension` | `'.wiki'` | wiki file extension |
 | `g:nuwiki_log_level` | `'warn'` | `error` \| `warn` \| `info` \| `debug` |
+| `g:nuwiki_link_severity` | `'warn'` | broken-link severity: `off` \| `hint` \| `warn` \| `error` |
 | `g:nuwiki_no_default_mappings` | `0` | `1` skips the keymap layer |
 | `g:nuwiki_no_folding` | `0` | `1` skips foldexpr setup |
 | `g:nuwiki_mouse_mappings` | `0` | `1` enables mouse maps |
 
-> **Note:** `diagnostic.link_severity` is accepted in the config surface but
-> the server currently always uses its default (`'warn'`); the client value is
-> not yet wired through. Track this if you rely on changing broken-link
-> severity.
-
 ---
 
 ## Usage

development/tests/config-expected.txt

@@ -3,11 +3,13 @@ wiki_root=~/vimwiki
 file_extension=.wiki
 syntax=vimwiki
 log_level=warn
+diagnostic.link_severity=warn
 [sample]
 wiki_root=/tmp/base
 file_extension=.md
 syntax=vimwiki
 log_level=debug
+diagnostic.link_severity=error
 wikis[0].diary_rel_path=journal
 wikis[0].file_extension=.wiki
 wikis[0].index=home

development/tests/test-config-vim.vim

@@ -15,6 +15,9 @@ function! s:dump(payload) abort
   call add(s:lines, 'file_extension=' . a:payload.file_extension)
   call add(s:lines, 'syntax=' . a:payload.syntax)
   call add(s:lines, 'log_level=' . a:payload.log_level)
+  if has_key(a:payload, 'diagnostic')
+    call add(s:lines, 'diagnostic.link_severity=' . a:payload.diagnostic.link_severity)
+  endif
   if has_key(a:payload, 'wikis')
     let l:i = 0
     for l:w in a:payload.wikis
@@ -28,7 +31,7 @@ endfunction
 
 " Scenario 1: defaults (no globals set).
 unlet! g:nuwiki_wiki_root g:nuwiki_file_extension g:nuwiki_syntax
-unlet! g:nuwiki_log_level g:nuwiki_wikis
+unlet! g:nuwiki_log_level g:nuwiki_wikis g:nuwiki_link_severity
 call add(s:lines, '[default]')
 call s:dump(nuwiki#lsp#settings())
 
@@ -37,6 +40,7 @@ let g:nuwiki_wiki_root      = '/tmp/base'
 let g:nuwiki_file_extension = '.md'
 let g:nuwiki_syntax         = 'vimwiki'
 let g:nuwiki_log_level      = 'debug'
+let g:nuwiki_link_severity  = 'error'
 let g:nuwiki_wikis = [
       \ { 'name': 'personal', 'root': '/tmp/personal',
       \   'file_extension': '.wiki', 'index': 'home',

development/tests/test-config.lua

@@ -27,6 +27,9 @@ local function dump(payload)
   emit('file_extension=' .. tostring(payload.file_extension))
   emit('syntax=' .. tostring(payload.syntax))
   emit('log_level=' .. tostring(payload.log_level))
+  if payload.diagnostic then
+    emit('diagnostic.link_severity=' .. tostring(payload.diagnostic.link_severity))
+  end
   if payload.wikis then
     for i, w in ipairs(payload.wikis) do
       local keys = {}
@@ -53,6 +56,7 @@ config.apply({
   file_extension = '.md',
   syntax = 'vimwiki',
   log_level = 'debug',
+  diagnostic = { link_severity = 'error' },
   wikis = {
     {
       name = 'personal',