Baseline: Ludic compiler + toolchain, Phase 1 syntax fixes complete

Self-hosted compiler (selfhost/*.ludic), runtime, examples, editor tooling,
and docs. Phase 1 of the syntax-redesign cohesion pass has landed:
edge-system fix, signature-query, when-alias, and the documentation truth-pass.
Suite green (14/14), C-free bootstrap fixpoint holds.

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

tools/editors/neovim/lua/ludic.lua

@@ -0,0 +1,86 @@
+-- Ludic support for Neovim (0.9+), with no plugin manager and no dependencies.
+--
+--   :lua require('ludic').setup()
+--   -- or, from init.lua:
+--   vim.opt.runtimepath:append('/path/to/gpp/tools/editors/neovim')
+--   require('ludic').setup({ server = '/path/to/gpp/build/ludic-lsp' })
+--
+-- Highlighting here comes from the language server's semantic tokens, which
+-- Neovim applies natively -- there is no tree-sitter grammar to install and no
+-- second copy of the vocabulary to keep in sync.
+
+local M = {}
+
+local function find_executable(names, roots, subdirs)
+  for _, root in ipairs(roots) do
+    for _, sub in ipairs(subdirs) do
+      for _, name in ipairs(names) do
+        local p = root .. '/' .. sub .. '/' .. name
+        if vim.fn.executable(p) == 1 then return p end
+      end
+    end
+  end
+  for _, name in ipairs(names) do
+    if vim.fn.executable(name) == 1 then return name end
+  end
+  return nil
+end
+
+function M.setup(opts)
+  opts = opts or {}
+
+  -- .ludic files are Ludic
+  vim.filetype.add({ extension = { ludic = 'ludic' } })
+
+  vim.api.nvim_create_autocmd('FileType', {
+    pattern = 'ludic',
+    callback = function()
+      vim.bo.commentstring = '# %s'
+      vim.bo.comments = ':#'
+      vim.bo.expandtab = true
+      vim.bo.shiftwidth = opts.indent or 2
+      vim.bo.tabstop = opts.indent or 2
+    end,
+  })
+
+  local root_markers = { 'build.sh', 'LANGUAGE.md', '.git' }
+
+  local function root_dir(fname)
+    local found = vim.fs.find(root_markers, { path = vim.fs.dirname(fname), upward = true })[1]
+    return found and vim.fs.dirname(found) or vim.fs.dirname(fname)
+  end
+
+  vim.api.nvim_create_autocmd('FileType', {
+    -- markdown is included on purpose: ```ludic fences get diagnostics and
+    -- semantic highlighting like any source file
+    pattern = { 'ludic', 'markdown' },
+    callback = function(args)
+      local root = root_dir(vim.api.nvim_buf_get_name(args.buf))
+      local server = opts.server or find_executable(
+        { 'ludic-lsp' }, { root }, { 'build', 'tools/build', 'bin', '.' })
+      if not server then return end
+      local compiler = opts.compiler or find_executable(
+        { 'ludicc' }, { root }, { 'build', 'bin', '.' }) or ''
+
+      vim.lsp.start({
+        name = 'ludic-lsp',
+        cmd = { server, '--stdio' },
+        root_dir = root,
+        init_options = {
+          compilerPath = compiler,
+          compilerDiagnostics = opts.compiler_diagnostics ~= false,
+          indentSize = opts.indent or 2,
+        },
+      }, { bufnr = args.buf })
+    end,
+  })
+
+  if opts.format_on_save ~= false then
+    vim.api.nvim_create_autocmd('BufWritePre', {
+      pattern = { '*.ludic' },
+      callback = function() vim.lsp.buf.format({ async = false, timeout_ms = 2000 }) end,
+    })
+  end
+end
+
+return M