fix(nixvim): eliminate per-keystroke LSP completion latency

- drop lsp-lines (redundant with tiny-inline-diagnostic; double diagnostic virtual-text redraw per keystroke)
- drop nvim_lsp_signature_help cmp source (extra server request per keystroke; <C-k> keymap covers it)
- remove cmp-nvim-lsp-signature-help plugin (now unused)
- disable LSP client file logging (nixd/svelte stderr spam was writing 5MB+ logs on the main loop)
- disable rust-analyzer semantic tokens (ContentModified retry loop while typing)

config/modules/nixvim/default.nix

@@ -121,9 +121,14 @@
                   };
                 };
               };
-              lsp = {
-                enable = true;
-                servers = {
+                  lsp = {
+                    enable = true;
+                    onAttach = ''
+                      if client.name == "rust-analyzer" then
+                        client.server_capabilities.semanticTokensProvider = nil
+                      end
+                    '';
+                    servers = {
                   # qmlls = {
                   #   enable = true;
                   #   config = {
@@ -224,7 +229,6 @@
                   };
                 };
               };
-              lsp-lines.enable = true;
               trouble = {
                 enable = true;
                 settings = {
@@ -257,10 +261,6 @@
                       name = "nvim_lsp";
                       priority = 100;
                     }
-                    {
-                      name = "nvim_lsp_signature_help";
-                      priority = 90;
-                    }
                     {
                       name = "luasnip";
                       priority = 75;
@@ -340,7 +340,6 @@
               };
             };
             extraPlugins = with pkgs; [
-              vimPlugins.cmp-nvim-lsp-signature-help
               tiny-code-action
             ];
             opts = {
@@ -355,6 +354,8 @@
               mapleader = " ";
             };
             extraConfigLua = ''
+              -- LSP client writes server stderr + errors to disk on the main loop; nixd spams info logs -> 5MB+ logs. Kill it.
+              vim.lsp.set_log_level("off")
               -- tree-sitter-nix uses (#is-not? local) which the new nvim-treesitter main branch no longer registers
               vim.treesitter.query.add_predicate("is-not?", function() return true end, { force = true })