From 335990afa5f2ae51f2af9c1ca926ec6b8954b906 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Kuba=20Podg=C3=B3rski?=
 <4056521+kuba--@users.noreply.github.com>
Date: Sun, 9 Aug 2026 09:42:24 +0200
Subject: [PATCH] return psrpc.FailedPrecondition for "participant client
 version does not support moving" error (#4736)

---
 pkg/rtc/participant.go               |  9 +++++++--
 pkg/rtc/participant_internal_test.go | 21 +++++++++++++++++++++
 2 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/pkg/rtc/participant.go b/pkg/rtc/participant.go
index 8a8f0a768..2d86565f6 100644
--- a/pkg/rtc/participant.go
+++ b/pkg/rtc/participant.go
@@ -83,7 +83,7 @@ const (
 )
 
 var (
-	ErrMoveOldClientVersion = errors.New("participant client version does not support moving")
+	ErrMoveOldClientVersion = psrpc.NewErrorf(psrpc.FailedPrecondition, "participant client version does not support moving")
 )
 
 // -------------------------------------------------
@@ -4103,7 +4103,12 @@ func (p *ParticipantImpl) SupportsMoving() error {
 	}
 
 	if kind := p.Kind(); kind == livekit.ParticipantInfo_EGRESS || kind == livekit.ParticipantInfo_AGENT || p.params.UseOneShotSignallingMode {
-		return fmt.Errorf("%s participants cannot be moved, one-shot signaling mode: %t", kind.String(), p.params.UseOneShotSignallingMode)
+		return psrpc.NewErrorf(
+			psrpc.FailedPrecondition,
+			"%s participants cannot be moved, one-shot signaling mode: %t",
+			kind.String(),
+			p.params.UseOneShotSignallingMode,
+		)
 	}
 
 	return nil
diff --git a/pkg/rtc/participant_internal_test.go b/pkg/rtc/participant_internal_test.go
index 68c7277e4..33263a360 100644
--- a/pkg/rtc/participant_internal_test.go
+++ b/pkg/rtc/participant_internal_test.go
@@ -22,6 +22,7 @@ import (
 
 	"github.com/pion/webrtc/v4"
 	"github.com/stretchr/testify/require"
+	"github.com/twitchtv/twirp"
 	"go.uber.org/atomic"
 	"google.golang.org/protobuf/proto"
 
@@ -77,6 +78,26 @@ func TestIsReady(t *testing.T) {
 	}
 }
 
+func TestSupportsMoving(t *testing.T) {
+	t.Run("current protocol version", func(t *testing.T) {
+		p := newParticipantForTestWithOpts("test", &participantOpts{protocolVersion: types.CurrentProtocol})
+		require.NoError(t, p.SupportsMoving())
+	})
+
+	// a move rejected because of what the participant is cannot be retried into working, but it is
+	// still a caller error, so it has to surface as a 4xx rather than a 500
+	t.Run("client version that cannot be moved", func(t *testing.T) {
+		p := newParticipantForTestWithOpts("test", &participantOpts{protocolVersion: 6})
+
+		err := p.SupportsMoving()
+		require.ErrorIs(t, err, ErrMoveOldClientVersion)
+
+		var twirpErr twirp.Error
+		require.ErrorAs(t, err, &twirpErr)
+		require.Equal(t, twirp.FailedPrecondition, twirpErr.Code())
+	})
+}
+
 func TestTrackPublishing(t *testing.T) {
 	t.Run("should send the correct events", func(t *testing.T) {
 		p := newParticipantForTest("test")