usbip: fix E.New(fmt.Sprintf) and banned if-init error checks

Replace E.New(fmt.Sprintf("...0x%04x", v)) with variadic E.New(..., fmt.Sprintf("0x%04x", v)) so plain text and integer args flow through F.ToString (sing-box/common/stun/stun.go precedent). Hoist three sysfs_linux.go if-init error checks per .claude/rules/go-syntax.md ("assign first, then check"); two of them also shadowed the outer err.

service/usbip/client.go

@@ -196,10 +196,10 @@ func (c *ClientService) attemptAttach(ctx context.Context, busid string) (Attach
 		return nil, E.Cause(err, "read OP_REP_IMPORT header")
 	}
 	if header.Version != ProtocolVersion {
-		return nil, E.New(fmt.Sprintf("unexpected reply version 0x%04x", header.Version))
+		return nil, E.New("unexpected reply version ", fmt.Sprintf("0x%04x", header.Version))
 	}
 	if header.Code != expectedReply {
-		return nil, E.New(fmt.Sprintf("unexpected reply code 0x%04x", header.Code))
+		return nil, E.New("unexpected reply code ", fmt.Sprintf("0x%04x", header.Code))
 	}
 	if header.Status != OpStatusOK {
 		return nil, E.New("remote rejected import (status=", header.Status, ")")

service/usbip/client_shared.go

@@ -502,10 +502,10 @@ func (c *ClientService) fetchDevList(ctx context.Context) ([]DeviceEntry, error)
 		return nil, E.Cause(err, "read OP_REP_DEVLIST header")
 	}
 	if header.Version != ProtocolVersion {
-		return nil, E.New(fmt.Sprintf("unexpected reply version 0x%04x", header.Version))
+		return nil, E.New("unexpected reply version ", fmt.Sprintf("0x%04x", header.Version))
 	}
 	if header.Code != OpRepDevList || header.Status != OpStatusOK {
-		return nil, E.New(fmt.Sprintf("OP_REP_DEVLIST status=%d code=0x%04x", header.Status, header.Code))
+		return nil, E.New("OP_REP_DEVLIST status=", header.Status, " code=", fmt.Sprintf("0x%04x", header.Code))
 	}
 	return ReadOpRepDevListBody(conn)
 }

service/usbip/host_darwin.go

@@ -534,7 +534,7 @@ func (s *darwinServerDataSession) serve() error {
 				return err
 			}
 		default:
-			return E.New(fmt.Sprintf("unexpected USB/IP command 0x%08x", header.Command))
+			return E.New("unexpected USB/IP command ", fmt.Sprintf("0x%08x", header.Command))
 		}
 	}
 }

service/usbip/sysfs_linux.go

@@ -107,11 +107,13 @@ func readSysfsDevice(busid, path string) (sysfsDevice, error) {
 	d.VendorID = vendor
 	d.ProductID, _ = readHexU16(path, "idProduct")
 	d.BCDDevice, _ = readHexU16(path, "bcdDevice")
-	if v, err := readDecU32(path, "busnum"); err == nil {
-		d.BusNum = v
+	busNum, err := readDecU32(path, "busnum")
+	if err == nil {
+		d.BusNum = busNum
 	}
-	if v, err := readDecU32(path, "devnum"); err == nil {
-		d.DevNum = v
+	devNum, err := readDecU32(path, "devnum")
+	if err == nil {
+		d.DevNum = devNum
 	}
 	d.Speed = speedCodeFromString(readString(path, "speed"))
 	d.DeviceClass, _ = readHexU8(path, "bDeviceClass")
@@ -334,13 +336,14 @@ func ensureKernelPath(path string, module string, description string) error {
 }
 
 func findModprobePath() (string, error) {
-	if path, err := exec.LookPath("modprobe"); err == nil {
-		return path, nil
+	modprobePath, err := exec.LookPath("modprobe")
+	if err == nil {
+		return modprobePath, nil
 	}
-	for _, path := range []string{"/usr/sbin/modprobe", "/sbin/modprobe", "/usr/bin/modprobe", "/bin/modprobe"} {
-		info, err := os.Stat(path)
-		if err == nil && info.Mode().IsRegular() && info.Mode()&0o111 != 0 {
-			return path, nil
+	for _, candidate := range []string{"/usr/sbin/modprobe", "/sbin/modprobe", "/usr/bin/modprobe", "/bin/modprobe"} {
+		info, statErr := os.Stat(candidate)
+		if statErr == nil && info.Mode().IsRegular() && info.Mode()&0o111 != 0 {
+			return candidate, nil
 		}
 	}
 	return "", E.New("modprobe executable not found")

service/usbip/usbip_peer.go

@@ -270,7 +270,7 @@ func (p *UsbIpPeer) readLoop() {
 			}
 			transaction.finalize(SubmitResponse{}, ErrCanceled)
 		default:
-			p.setReadError(E.New(fmt.Sprintf("unexpected USB/IP response 0x%08x", header.Command)))
+			p.setReadError(E.New("unexpected USB/IP response ", fmt.Sprintf("0x%08x", header.Command)))
 			return
 		}
 	}