feat: Replace python tests with native E2E test suite and fix capabilities schema

- Added native E2E test suite in stub to validate server<->stub<->nvim IPC
- Added win-nvim integration tests
- Fixed empty capabilities schema in initialize response in server and win-nvim
- Refactored server to accept dynamic MCP_PORT for test isolation
- Made server exit gracefully on port 3000 collision

win-nvim/tests/integration_test.rs

@@ -0,0 +1,111 @@
+use serde_json::{json, Value};
+use std::io::{BufRead, BufReader, Read, Write};
+use std::process::{Command, Stdio};
+use std::time::Duration;
+
+fn send_message(stdin: &mut std::process::ChildStdin, msg: Value) {
+    let s = serde_json::to_string(&msg).unwrap();
+    let payload = format!("Content-Length: {}\r\n\r\n{}", s.len(), s);
+    stdin.write_all(payload.as_bytes()).unwrap();
+    stdin.flush().unwrap();
+}
+
+fn read_message(stdout: &mut std::process::ChildStdout) -> Option<Value> {
+    let mut reader = BufReader::new(stdout);
+    let mut length = 0;
+    
+    // Read headers
+    loop {
+        let mut line = String::new();
+        if reader.read_line(&mut line).unwrap_or(0) == 0 {
+            return None; // EOF
+        }
+        let line = line.trim_end();
+        if line.is_empty() {
+            break;
+        }
+        if let Some(len_str) = line.strip_prefix("Content-Length: ") {
+            length = len_str.parse().unwrap_or(0);
+        }
+    }
+    
+    if length == 0 {
+        return None;
+    }
+    
+    // Read body
+    let mut buf = vec![0u8; length];
+    reader.read_exact(&mut buf).unwrap();
+    let body_str = String::from_utf8_lossy(&buf);
+    
+    Some(serde_json::from_str(&body_str).unwrap())
+}
+
+#[test]
+fn test_mcp_initialization_and_tools_list() {
+    // Determine the path to the built binary.
+    // cargo test automatically sets CARGO_BIN_EXE_<name> for binary targets!
+    let exe_path = env!("CARGO_BIN_EXE_mcp-memory-win-nvim");
+    
+    let mut child = Command::new(exe_path)
+        .stdin(Stdio::piped())
+        .stdout(Stdio::piped())
+        .stderr(Stdio::piped())
+        .spawn()
+        .expect("Failed to start mcp-memory-win-nvim");
+
+    let mut stdin = child.stdin.take().expect("Failed to open stdin");
+    let mut stdout = child.stdout.take().expect("Failed to open stdout");
+
+    // 1. Test Initialize
+    let init_req = json!({
+        "jsonrpc": "2.0",
+        "method": "initialize",
+        "params": {
+            "protocolVersion": "2024-11-05",
+            "capabilities": {},
+            "clientInfo": {
+                "name": "test-client",
+                "version": "1.0"
+            }
+        },
+        "id": 1
+    });
+
+    send_message(&mut stdin, init_req);
+    
+    let init_resp = read_message(&mut stdout).expect("Failed to read initialize response");
+    
+    assert_eq!(init_resp["jsonrpc"], "2.0");
+    assert_eq!(init_resp["id"], 1);
+    
+    // VERIFY CRITICAL FIX: Ensure capabilities.tools is present!
+    let capabilities = &init_resp["result"]["capabilities"];
+    assert!(capabilities.get("tools").is_some(), "capabilities.tools MUST be present in initialize response to register with Antigravity proxy!");
+
+    // 2. Test tools/list
+    let tools_req = json!({
+        "jsonrpc": "2.0",
+        "method": "tools/list",
+        "params": {},
+        "id": 2
+    });
+    
+    send_message(&mut stdin, tools_req);
+    
+    let tools_resp = read_message(&mut stdout).expect("Failed to read tools/list response");
+    
+    assert_eq!(tools_resp["jsonrpc"], "2.0");
+    assert_eq!(tools_resp["id"], 2);
+    
+    let tools = tools_resp["result"]["tools"].as_array().expect("result.tools must be an array");
+    assert!(!tools.is_empty(), "Server must expose at least one tool");
+    
+    // Verify a specific tool exists
+    let has_get_active_buffer = tools.iter().any(|t| t["name"] == "nvim_get_active_buffer");
+    assert!(has_get_active_buffer, "Missing nvim_get_active_buffer tool");
+
+    // Kill the child process cleanly
+    child.kill().expect("Failed to kill child");
+    child.wait().expect("Failed to wait on child");
+}