fix(vars): E121 in get_wikilocal no-index path; add regression test

s:resolve_index referenced an undefined `a:file` (a copy-paste leftover
from wiki_root_for, whose parameter is named a:file) inside the
buffer-owning-wiki loop. Any get_wikilocal() call with no explicit index
while a wiki buffer was current — i.e. the ftplugin BufRead path — hit
`E121: undefined variable a:file`. The local is `l:file`, and the
surrounding `!empty(l:file)` guard already covers emptiness, so the
clause was both wrong and redundant; removed it.

Add development/tests/test-vars-vim.{sh,vim} covering the shim:
per-wiki-index resolution, global-default fallback, out-of-range clamp,
the no-index owning-wiki path (direct guard for this E121), and the
single-wiki shorthand. Wired into CI. 14/14 pass.

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

development/tests/test-vars-vim.vim

@@ -0,0 +1,57 @@
+" development/tests/test-vars-vim.vim — exercises the vimwiki compat shim
+" (autoload/vimwiki/vars.vim) that third-party plugins call.
+"
+" Sourced by test-vars-vim.sh under headless Vim. Writes PASS/FAIL lines to
+" $NUWIKI_VARS_OUT; the shell wrapper fails on any FAIL (or missing output).
+
+let s:out = []
+let s:dir_a = $NUWIKI_VARS_DIR_A
+let s:dir_b = $NUWIKI_VARS_DIR_B
+
+function! s:check(desc, got, want) abort
+  if a:got ==# a:want
+    call add(s:out, 'PASS ' . a:desc)
+  else
+    call add(s:out, 'FAIL ' . a:desc . '  got=[' . a:got . '] want=[' . a:want . ']')
+  endif
+endfunction
+
+" ----- multi-wiki: explicit index -----
+let g:nuwiki_wikis = [
+  \ {'root': s:dir_a, 'file_extension': 'wiki', 'syntax': 'markdown'},
+  \ {'root': s:dir_b, 'file_extension': '.wiki'},
+  \ ]
+let g:nuwiki_syntax = 'vimwiki'
+
+call s:check('idx0 path',   vimwiki#vars#get_wikilocal('path', 0),      s:dir_a . '/')
+call s:check('idx0 ext',    vimwiki#vars#get_wikilocal('ext', 0),       '.wiki')
+call s:check('idx0 syntax', vimwiki#vars#get_wikilocal('syntax', 0),    'markdown')
+" wiki[1] doesn't set syntax → global default
+call s:check('idx1 path',   vimwiki#vars#get_wikilocal('path', 1),      s:dir_b . '/')
+call s:check('idx1 syntax', vimwiki#vars#get_wikilocal('syntax', 1),    'vimwiki')
+" out-of-range clamps to first wiki
+call s:check('idx9 clamp',  vimwiki#vars#get_wikilocal('path', 9),      s:dir_a . '/')
+" misc keys
+call s:check('is_temporary', vimwiki#vars#get_wikilocal('is_temporary_wiki', 0) . '', '0')
+call s:check('unknown key',  vimwiki#vars#get_wikilocal('bogus', 0),    '')
+
+" ----- no index: resolve the wiki owning the current buffer -----
+" (this is the BufRead path; regression guard for the s:resolve_index E121.)
+execute 'edit ' . fnameescape(s:dir_b . '/index.wiki')
+call s:check('noarg owning wiki_b', vimwiki#vars#get_wikilocal('path'), s:dir_b . '/')
+execute 'edit ' . fnameescape(s:dir_a . '/index.wiki')
+call s:check('noarg owning wiki_a', vimwiki#vars#get_wikilocal('path'), s:dir_a . '/')
+" buffer outside any wiki → first wiki
+enew
+call s:check('noarg outside→first', vimwiki#vars#get_wikilocal('path'), s:dir_a . '/')
+
+" ----- single-wiki shorthand (no g:nuwiki_wikis) -----
+unlet g:nuwiki_wikis
+let g:nuwiki_wiki_root = s:dir_a
+let g:nuwiki_file_extension = 'txt'
+enew
+call s:check('shorthand path',   vimwiki#vars#get_wikilocal('path'),   s:dir_a . '/')
+call s:check('shorthand ext',    vimwiki#vars#get_wikilocal('ext'),    '.txt')
+call s:check('shorthand syntax', vimwiki#vars#get_wikilocal('syntax'), 'vimwiki')
+
+call writefile(s:out, $NUWIKI_VARS_OUT)