Raise host frame payload limit so multi-client UART replies fit.

Use a uint16 LE length and 1024-byte max payload so CLIENT_INFO and BATTERY_STATUS no longer fail encoding past ~10 connected pods.

Co-authored-by: Cursor <cursoragent@cursor.com>

goTool/uart/frame.go

@@ -10,8 +10,10 @@ import (
 const (
 	StartMarker = 0xAA
 	StopMarker  = 0xCC
-	// Must match main/uart.h MAX_PAYLOAD_SIZE (MAX_BUF_SIZE - 4).
-	MaxPayload = 248
+	// Must match main/uart.h MAX_PAYLOAD_SIZE.
+	MaxPayload = 1024
+	// AA | len_lo | len_hi | payload | xor | CC
+	FrameOverhead = 5
 )
 
 var (
@@ -19,14 +21,15 @@ var (
 	ErrTimeout      = errors.New("read timeout")
 )
 
-// EncodeFrame builds a framed packet: 0xAA len payload xor(payload) 0xCC.
+// EncodeFrame builds a framed packet: 0xAA len_lo len_hi payload xor(payload) 0xCC.
 func EncodeFrame(payload []byte) ([]byte, error) {
 	if len(payload) == 0 || len(payload) > MaxPayload {
 		return nil, fmt.Errorf("payload length %d out of range 1..%d", len(payload), MaxPayload)
 	}
 
-	frame := make([]byte, 0, 4+len(payload))
-	frame = append(frame, StartMarker, byte(len(payload)))
+	n := len(payload)
+	frame := make([]byte, 0, FrameOverhead+n)
+	frame = append(frame, StartMarker, byte(n&0xff), byte((n>>8)&0xff))
 	var checksum byte
 	for _, b := range payload {
 		frame = append(frame, b)
@@ -39,6 +42,7 @@ func EncodeFrame(payload []byte) ([]byte, error) {
 type Parser struct {
 	state    int
 	len      int
+	lenLo    byte
 	payload  []byte
 	index    int
 	checksum byte
@@ -46,7 +50,8 @@ type Parser struct {
 
 const (
 	stateStart = iota
-	stateLen
+	stateLenLo
+	stateLenHi
 	stateData
 	stateChecksum
 	stateStop
@@ -63,14 +68,19 @@ func (p *Parser) Feed(b byte) (payload []byte, ok bool, err error) {
 		if b == StartMarker {
 			p.index = 0
 			p.checksum = 0
-			p.state = stateLen
+			p.state = stateLenLo
 		}
-	case stateLen:
-		if b == 0 || b > MaxPayload {
+	case stateLenLo:
+		p.lenLo = b
+		p.state = stateLenHi
+	case stateLenHi:
+		n := int(p.lenLo) | (int(b) << 8)
+		if n == 0 || n > MaxPayload {
 			p.state = stateStart
 		} else {
-			p.len = int(b)
+			p.len = n
 			p.payload = make([]byte, p.len)
+			p.index = 0
 			p.state = stateData
 		}
 	case stateData:
@@ -102,7 +112,7 @@ func (p *Parser) Feed(b byte) (payload []byte, ok bool, err error) {
 // maxWait bounds total wait time; zero means no limit (serial read timeouts retry forever).
 func ReadFrame(r io.Reader, buf []byte, maxWait time.Duration) ([]byte, error) {
 	if buf == nil {
-		buf = make([]byte, 256)
+		buf = make([]byte, 1024)
 	}
 	parser := NewParser()