perf: fix slice boundary panics, eliminate string allocation in stdio reader, fix lua table nesting bug, and optimize nvim socket chunk size

nvim-core/src/lib.rs

@@ -25,7 +25,7 @@ pub async fn send_response(response: JsonRpcResponse) {
     tracing::info!(
         "Sending JSON-RPC response (id: {:?}): {}{}",
         response.id,
-        &msg[..std::cmp::min(msg.len(), 500)],
+        &msg[..msg.floor_char_boundary(500)],
         if msg.len() > 500 { "..." } else { "" }
     );
     // CRITICAL ARCHITECTURAL DECISION:
@@ -182,7 +182,7 @@ async fn get_nvim_connection() -> Result<mpsc::Sender<NvimRequest>, String> {
     let pending_clone2 = Arc::clone(&pending_requests);
     tokio::spawn(async move {
         let mut resp_buf = Vec::new();
-        let mut chunk = vec![0u8; 8192];
+        let mut chunk = vec![0u8; 65536];
         let mut offset = 0;
 
         loop {
@@ -957,7 +957,7 @@ pub async fn run_mcp_loop(app_name: &str, app_version: &str) {
                                 local first = vim.fn.line('w0')
                                 local last = vim.fn.line('w$')
                                 local lines = vim.api.nvim_buf_get_lines(0, first - 1, last, false)
-                                local res = {{}}
+                                local res = {}
                                 for i, line in ipairs(lines) do
                                     table.insert(res, tostring(first + i - 1) .. ': ' .. line)
                                 end