feat(config): vimwiki drop-in config + global per-wiki defaults

Two related config-ergonomics features for vimwiki migrants, sharing the
same scalar-global machinery.

1. Upstream g:vimwiki_* drop-in (Vim client). When nuwiki isn't configured
   natively, the Vim client reads g:vimwiki_list + g:vimwiki_* globals and
   translates them into nuwiki's schema: per-wiki path->root,
   path_html->html_path, template_*, css_name, auto_export/auto_toc,
   syntax, ext->file_extension, index, diary_*, name. g:nuwiki_* always
   wins. Lets a vimwiki user drop in nuwiki without rewriting config.

2. Global per-wiki defaults (both clients). A display/generation setting
   given once at the top level — g:nuwiki_<key> / setup({<key>=…}) /
   g:vimwiki_<key> — is folded into every wiki as a default; a per-wiki
   value overrides it (vimwiki's model). Covers toc_header(_level),
   toc_link_format, links_header(_level), tags_header(_level),
   html_header_numbering(_sym), links_space_char, list_margin, listsyms,
   listsym_rejected, and the auto_* toggles. Only values the user
   explicitly set fold — built-in defaults don't (added config.user
   tracking on the Lua side so a default toc_header_level=1 isn't pushed
   onto every wiki). User config tables are never mutated.

Both clients kept in lock-step (config-parity golden enforces identical
payloads). New harnesses test-vimwiki-compat-vim (18) and
test-global-shorthand (8), wired into CI. Server test
vimwiki_compat_payload_sets_toc_level_per_wiki. Docs in README +
known-issues.md (drop-in is currently Vim-only). Rust 573 passed, clippy
clean, all harnesses green.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

autoload/nuwiki/lsp.vim

@@ -12,6 +12,97 @@ let s:plugin_root = fnamemodify(resolve(expand('<sfile>:p')), ':h:h:h')
 
 let s:started = 0
 
+" ===== Upstream vimwiki config compatibility =====
+"
+" nuwiki is a drop-in vimwiki replacement, so a user who keeps their original
+" `g:vimwiki_list` + `g:vimwiki_*` globals shouldn't have to rewrite anything.
+" These tables translate the upstream names into the server's config schema.
+" nuwiki-native config (`g:nuwiki_wikis` / `g:nuwiki_*`) always wins.
+
+" Per-wiki dict keys: upstream `g:vimwiki_list[i]` key -> server key.
+let s:vimwiki_wiki_map = {
+      \ 'path':             'root',
+      \ 'path_html':        'html_path',
+      \ 'template_path':    'template_path',
+      \ 'template_default': 'template_default',
+      \ 'template_ext':     'template_ext',
+      \ 'css_name':         'css_name',
+      \ 'auto_export':      'auto_export',
+      \ 'auto_toc':         'auto_toc',
+      \ 'syntax':           'syntax',
+      \ 'ext':              'file_extension',
+      \ 'index':            'index',
+      \ 'diary_rel_path':   'diary_rel_path',
+      \ 'diary_index':      'diary_index',
+      \ 'name':             'name',
+      \ }
+
+" Global scalar settings vimwiki applies to every wiki (via wikilocal
+" defaults): upstream suffix (`g:vimwiki_<suffix>`) -> server key. The server
+" reads these per-wiki, so we fold them into each wiki entry (and into the
+" single-wiki shorthand payload).
+let s:scalar_global_map = {
+      \ 'toc_header':                'toc_header',
+      \ 'toc_header_level':          'toc_header_level',
+      \ 'toc_link_format':           'toc_link_format',
+      \ 'links_header':              'links_header',
+      \ 'links_header_level':        'links_header_level',
+      \ 'tags_header':               'tags_header',
+      \ 'tags_header_level':         'tags_header_level',
+      \ 'html_header_numbering':     'html_header_numbering',
+      \ 'html_header_numbering_sym': 'html_header_numbering_sym',
+      \ 'links_space_char':          'links_space_char',
+      \ 'list_margin':               'list_margin',
+      \ 'listsyms':                  'listsyms',
+      \ 'listsym_rejected':          'listsym_rejected',
+      \ 'auto_export':               'auto_export',
+      \ 'auto_toc':                  'auto_toc',
+      \ 'auto_generate_links':       'auto_generate_links',
+      \ 'auto_generate_tags':        'auto_generate_tags',
+      \ 'auto_diary_index':          'auto_diary_index',
+      \ }
+
+" Resolve the per-wiki scalar globals: vimwiki values first (compat), then
+" nuwiki-native `g:nuwiki_<key>` overrides on top.
+function! s:scalar_globals() abort
+  let l:g = {}
+  for [l:src, l:dst] in items(s:scalar_global_map)
+    if exists('g:vimwiki_' . l:src)
+      let l:g[l:dst] = get(g:, 'vimwiki_' . l:src)
+    endif
+  endfor
+  for l:dst in values(s:scalar_global_map)
+    if exists('g:nuwiki_' . l:dst)
+      let l:g[l:dst] = get(g:, 'nuwiki_' . l:dst)
+    endif
+  endfor
+  return l:g
+endfunction
+
+" Build nuwiki's `wikis` list from an upstream `g:vimwiki_list`, folding the
+" global scalar settings into each entry. Returns [] when unset/malformed.
+function! s:wikis_from_vimwiki() abort
+  if !exists('g:vimwiki_list') || type(g:vimwiki_list) != type([]) || empty(g:vimwiki_list)
+    return []
+  endif
+  let l:globals = s:scalar_globals()
+  let l:wikis = []
+  for l:vw in g:vimwiki_list
+    if type(l:vw) != type({}) | continue | endif
+    let l:w = copy(l:globals)
+    for [l:src, l:dst] in items(s:vimwiki_wiki_map)
+      if has_key(l:vw, l:src)
+        let l:w[l:dst] = l:vw[l:src]
+      endif
+    endfor
+    " A wiki needs a root; skip entries without one.
+    if has_key(l:w, 'root')
+      call add(l:wikis, l:w)
+    endif
+  endfor
+  return l:wikis
+endfunction
+
 function! nuwiki#lsp#start() abort
   if s:started
     return
@@ -89,12 +180,29 @@ function! s:settings() abort
         \   'link_severity': get(g:, 'nuwiki_link_severity', 'warn'),
         \ },
         \ }
-  " Include the per-wiki list when configured via g:nuwiki_wikis so the
-  " server knows each wiki's root, diary path, etc. Without this it only
-  " sees wiki_root and resolves links relative to that directory instead
-  " of the individual wiki's root.
+  " Global scalar settings (g:vimwiki_* then g:nuwiki_* overrides) act as
+  " defaults applied to every wiki, vimwiki-style. A per-wiki value always
+  " wins. Resolved once and folded into whichever wiki shape we send.
+  let l:globals = s:scalar_globals()
+
+  " Wiki list resolution, in priority order:
+  "   1. g:nuwiki_wikis        (native multi-wiki config)
+  "   2. g:vimwiki_list        (upstream vimwiki config — drop-in compat)
+  "   3. wiki_root shorthand   (single wiki)
+  " Without a list the server only sees wiki_root and resolves links relative
+  " to that directory instead of each individual wiki's root.
   if exists('g:nuwiki_wikis') && !empty(g:nuwiki_wikis)
-    let l:cfg['wikis'] = g:nuwiki_wikis
+    let l:cfg['wikis'] = map(copy(g:nuwiki_wikis),
+          \ {_, w -> extend(copy(l:globals), w, 'force')})
+  else
+    let l:vw_wikis = s:wikis_from_vimwiki()
+    if !empty(l:vw_wikis)
+      let l:cfg['wikis'] = l:vw_wikis
+    else
+      " Single-wiki shorthand: fold the global scalars into the top-level
+      " payload so the server's single-wiki desugaring honours them.
+      call extend(l:cfg, l:globals, 'force')
+    endif
   endif
   return l:cfg
 endfunction