feat: Implement lightweight UDP interactive UI for Neovim

- Rewrote gemini-ui.lua to send native Neovim prompt selections, Ghost Text diff accept/reject actions, and smart context highlighting directly to the backend via zero-latency UDP port 3002, entirely replacing the old xecute_agent terminal subprocesses.
- Added prompt_user and preview_diff extmark lua functions for non-destructive diff review.
- Updated the Rust backend mcp-memory-server UDP listener to ingest the new gent_ask and interactive schema payloads and route them to the EventBus.
- Updated README.md and instructions.md with UDP documentation.

gemini-ui.lua

@@ -55,35 +55,118 @@ function M.close_progress()
     end
 end
 
-local function execute_agent(prompt)
-    local cmd = { "agy", "--new-project", "-i", prompt }
-    
-    M.show_progress("Starting Antigravity...")
-    
-    -- termopen requires an empty and unmodified buffer
-    vim.api.nvim_buf_set_lines(progress_buf, 0, -1, false, {})
-    vim.bo[progress_buf].modified = false
-    
-    -- termopen will attach to the current buffer (which show_progress just focused)
-    job_id = vim.fn.termopen(cmd, {
-        on_exit = function(_, code)
-            job_id = nil
+local function send_udp(payload)
+    local uv = vim.uv or vim.loop
+    local client = uv.new_udp()
+    if client then
+        local ok, data = pcall(vim.fn.json_encode, payload)
+        if ok then
+            client:send(data, "127.0.0.1", 3002, function(err)
+                client:close()
+            end)
+        else
+            client:close()
         end
+    end
+end
+
+function M.prompt_user(prompt_text, options, request_id)
+    if options and #options > 0 then
+        vim.ui.select(options, { prompt = prompt_text }, function(choice, idx)
+            send_udp({
+                event = "agent_prompt_response",
+                request_id = request_id,
+                response = choice,
+                index = idx,
+                session_id = vim.v.servername
+            })
+        end)
+    else
+        vim.ui.input({ prompt = prompt_text }, function(input)
+            send_udp({
+                event = "agent_prompt_response",
+                request_id = request_id,
+                response = input,
+                session_id = vim.v.servername
+            })
+        end)
+    end
+end
+
+local ns_id = vim.api.nvim_create_namespace("gemini_ghost_text")
+local active_diffs = {}
+
+function M.preview_diff(diff_id, bufnr, start_row, end_row, new_lines)
+    bufnr = (bufnr == 0 or bufnr == nil) and vim.api.nvim_get_current_buf() or bufnr
+    local virt_lines = {}
+    for _, line in ipairs(new_lines) do
+        table.insert(virt_lines, {{line, "DiffAdd"}})
+    end
+    
+    local extmark_id = vim.api.nvim_buf_set_extmark(bufnr, ns_id, start_row, 0, {
+        virt_lines = virt_lines,
+        virt_lines_above = true,
     })
-    vim.cmd('startinsert')
+    
+    active_diffs[diff_id] = {
+        bufnr = bufnr,
+        start_row = start_row,
+        end_row = end_row,
+        new_lines = new_lines,
+        extmark_id = extmark_id
+    }
+    
+    if pcall(require, "notify") then
+        require("notify")("Ghost text diff added. Use <leader>aa to accept or <leader>ar to reject.", "info", { title = "Antigravity" })
+    else
+        print("Ghost text diff added. Use <leader>aa to accept or <leader>ar to reject.")
+    end
+end
+
+function M.accept_diff()
+    local diff_id, diff = next(active_diffs)
+    if not diff then
+        print("No active diffs to accept.")
+        return
+    end
+    
+    vim.api.nvim_buf_set_lines(diff.bufnr, diff.start_row, diff.end_row, false, diff.new_lines)
+    vim.api.nvim_buf_del_extmark(diff.bufnr, ns_id, diff.extmark_id)
+    active_diffs[diff_id] = nil
+    
+    send_udp({ event = "agent_diff_accepted", diff_id = diff_id, session_id = vim.v.servername })
+    print("Diff accepted.")
+end
+
+function M.reject_diff()
+    local diff_id, diff = next(active_diffs)
+    if not diff then
+        print("No active diffs to reject.")
+        return
+    end
+    
+    vim.api.nvim_buf_del_extmark(diff.bufnr, ns_id, diff.extmark_id)
+    active_diffs[diff_id] = nil
+    
+    send_udp({ event = "agent_diff_rejected", diff_id = diff_id, session_id = vim.v.servername })
+    print("Diff rejected.")
 end
 
 function M.ask_agent()
     local file = vim.api.nvim_buf_get_name(0)
     vim.ui.input({ prompt = 'Ask Agent: ' }, function(input)
         if not input or input == '' then return end
-        
-        local final_input = input
-        if file and file ~= "" then
-            final_input = input .. string.format(" [Context file: %s]", file)
-        end
-        
-        execute_agent(final_input)
+        local cursor = vim.api.nvim_win_get_cursor(0)
+        send_udp({
+            event = "agent_ask",
+            prompt = input,
+            file = file,
+            line = cursor[1],
+            col = cursor[2],
+            session_id = vim.v.servername
+        })
+        M.show_progress("Sent to Antigravity via UDP...")
+        vim.defer_fn(M.close_progress, 1500)
     end)
 end
 
@@ -97,12 +180,21 @@ function M.setup()
             if not input or input == '' then return end
             
             local file = vim.api.nvim_buf_get_name(0)
-            local context = string.format(" [Context: %s lines %d-%d]", file, csrow, cerow)
-            local final_input = input .. context
-            
-            execute_agent(final_input)
+            send_udp({
+                event = "agent_ask_selection",
+                prompt = input,
+                file = file,
+                start_row = csrow,
+                end_row = cerow,
+                session_id = vim.v.servername
+            })
+            M.show_progress("Sent selection to Antigravity via UDP...")
+            vim.defer_fn(M.close_progress, 1500)
         end)
     end, { desc = "Ask Antigravity Agent about selection", noremap = true, silent = true })
+
+    vim.keymap.set('n', '<leader>aa', M.accept_diff, { desc = "Accept Agent Diff", noremap = true, silent = true })
+    vim.keymap.set('n', '<leader>ar', M.reject_diff, { desc = "Reject Agent Diff", noremap = true, silent = true })
 end
 
 return M