fix(ultrabeam): flush stale replies (not seq-match) + instant moving flag

The antenna does NOT echo our sequence number — its replies carry their own
counter — so the previous seq-matching drained every reply and stalled status
updates. Revert to reading one reply per command, but flush any bytes left in
the stream before each command (drainStale): a reply left by a timed-out command
is discarded so the next read stays 1:1. readPacket also resyncs to the next STX.
This fixes the intermittent disconnects, phantom frequency jumps and wrong
element-length readings without depending on the seq.

Also: report motion for a short window right after a commanded move, so the
"moving" indicator and the Flex TX-inhibit fire the instant a band/pattern is
clicked instead of a poll (~2 s) later; the real motor state takes over once
polled.

internal/ultrabeam/ultrabeam_test.go

@@ -5,14 +5,14 @@ import (
 	"bytes"
 	"net"
 	"testing"
+	"time"
 )
 
-// A stale reply left in the stream by an earlier timed-out command must be
-// DRAINED, not taken for this command's reply. Without seq matching, a STATUS
-// query would return a lingering READ_BANDS/PROGRESS payload — which showed up
-// on a remote link as phantom frequencies (a spurious follow-loop re-tune) and
-// dropped connections.
-func TestSendCommandDrainsStaleReplyAndMatchesSeq(t *testing.T) {
+// sendCommand must flush any bytes already in the stream (a reply left by an
+// earlier timed-out command) before reading, then return the reply to THIS
+// command. The antenna does not echo our sequence number, so keeping the stream
+// clean is the only way to stay in sync.
+func TestSendCommandFlushesStaleThenReadsReply(t *testing.T) {
 	srvConn, cliConn := net.Pipe()
 	defer srvConn.Close()
 	defer cliConn.Close()
@@ -22,8 +22,14 @@ func TestSendCommandDrainsStaleReplyAndMatchesSeq(t *testing.T) {
 
 	errc := make(chan error, 1)
 	go func() {
-		// Read the request, learn its seq, then answer with a stale reply (wrong
-		// seq) FIRST, then the real one.
+		// Leftover from a "previous" command still sitting in the stream. The Write
+		// blocks until drainStale consumes it, so it is guaranteed flushed before
+		// the real exchange.
+		if _, err := srvConn.Write(c.buildPacket(9, UB_OK, []byte{0xDE, 0xAD})); err != nil {
+			errc <- err
+			return
+		}
+		// Now serve the actual request.
 		req, err := srv.readPacket()
 		if err != nil {
 			errc <- err
@@ -34,16 +40,8 @@ func TestSendCommandDrainsStaleReplyAndMatchesSeq(t *testing.T) {
 			errc <- err
 			return
 		}
-		staleSeq := (seq + 1) % 128
-		if _, err := srvConn.Write(c.buildPacket(staleSeq, UB_OK, []byte{0xAA, 0xBB})); err != nil {
-			errc <- err
-			return
-		}
-		if _, err := srvConn.Write(c.buildPacket(seq, UB_OK, []byte{0x11, 0x22, 0x33})); err != nil {
-			errc <- err
-			return
-		}
-		errc <- nil
+		_, err = srvConn.Write(c.buildPacket(seq, UB_OK, []byte{0x11, 0x22, 0x33}))
+		errc <- err
 	}()
 
 	payload, err := c.sendCommand(CMD_STATUS, nil)
@@ -51,7 +49,7 @@ func TestSendCommandDrainsStaleReplyAndMatchesSeq(t *testing.T) {
 		t.Fatalf("sendCommand: %v", err)
 	}
 	if !bytes.Equal(payload, []byte{0x11, 0x22, 0x33}) {
-		t.Fatalf("payload = % X, want 11 22 33 — stale reply not drained or seq not matched", payload)
+		t.Fatalf("payload = % X, want 11 22 33 — stale reply not flushed", payload)
 	}
 	if err := <-errc; err != nil {
 		t.Fatalf("server: %v", err)
@@ -78,3 +76,19 @@ func TestReadPacketResyncsToSTX(t *testing.T) {
 		t.Fatalf("seq=%d cmd=%d payload=% X, want 5 / OK / 01 02", seq, cmd, payload)
 	}
 }
+
+// A commanded move must report motion immediately (before the next status poll),
+// then fall back to the real motor state once the window elapses.
+func TestOptimisticMotionAfterCommand(t *testing.T) {
+	c := &Client{lastStatus: &Status{Connected: true, MotorsMoving: 0}}
+
+	c.moveCmdAt = time.Now()
+	if st, _ := c.GetStatus(); st.MotorsMoving == 0 {
+		t.Fatal("just after a move command, GetStatus should report motion")
+	}
+
+	c.moveCmdAt = time.Now().Add(-ubMoveOptimisticWindow - time.Second)
+	if st, _ := c.GetStatus(); st.MotorsMoving != 0 {
+		t.Fatal("past the window with motors idle, GetStatus must report no motion")
+	}
+}