fix(js): validate TCP.connect arguments before FFI setup

bend2/effs/tcp_connect.js

@@ -4,11 +4,11 @@
 // The socket is non-blocking for life: EINPROGRESS parks the computation
 // until the socket is writable, and then SO_ERROR says how the connect ended.
 function tcp_connect(host, port, k) {
-  const sys = io_sys();
   const at = io_addr(host, Number(port));
   if (at === null) {
     return io_fail(22);
   }
+  const sys = io_sys();
   const fd = sys.socket(2, 1, 0);
   if (fd < 0) {
     return io_fail(sys.errno());

tests/io/tcp_connect_no_ffi.bend

@@ -0,0 +1,21 @@
+# Invalid connect arguments answer EINVAL even when FFI initialization fails.
+# The JS twin models a host without bun:ffi; valid Node TCP stays unsupported.
+import Base
+
+def ffi_absent() -> IO(Unit):
+  import "./tcp_connect_no_ffi.js"
+
+def report(r: Result<&1, &1, U32 & String, Socket>) -> IO(Unit):
+  match r:
+    case Done{socket}:
+      Socket.close(socket)
+    case Fail{(code, message)}:
+      IO.print(U32.show(code))
+
+def main() -> IO(Unit):
+  do IO<Unit>:
+    ffi_absent()
+    r : Result<&1, &1, U32 & String, Socket> <- TCP.connect("127.0.0.256", 0)
+    report(r)
+
+#|22

tests/io/tcp_connect_no_ffi.js

@@ -0,0 +1,18 @@
+// Make io_sys initialization fail once, as on a host without bun:ffi.
+function ffi_absent_run() {
+  const prior = Object.getOwnPropertyDescriptor(globalThis, "BEND_SYS");
+  Object.defineProperty(globalThis, "BEND_SYS", {
+    configurable: true,
+    get() {
+      if (prior) {
+        Object.defineProperty(globalThis, "BEND_SYS", prior);
+      } else {
+        delete globalThis.BEND_SYS;
+      }
+      throw new Error("no ffi on this host");
+    },
+  });
+  return { $: CID(Unit) };
+}
+
+io_eff(CID(ffi_absent), ffi_absent_run);