fix(jellycompat): stop binding NUL advisory lock keys

#529 stripped NUL from durable playback-session JSON, but
replaceUnstartedNegotiation still joined token/device/item with U+0000
and bound that string as PostgreSQL text. Postgres rejects NUL in text
(SQLSTATE 22021), so every negotiated compat session with a DeviceId
failed to persist and stayed cache-only.

Join the lock key with chr(31) inside PostgreSQL, matching the marker
contribution lock, so the bind parameters stay valid text.

Co-authored-by: Quick <Quick104@users.noreply.github.com>

internal/jellycompat/playback_sessions_postgres.go

@@ -42,6 +42,13 @@ var (
 
 var jsonNULCodePoint = []byte(`\u0000`)
 
+// compatNegotiationLockSQL takes token, device ID, and route item ID as
+// separate text parameters and joins them with chr(31) inside PostgreSQL.
+const compatNegotiationLockSQL = `
+		SELECT pg_advisory_xact_lock(
+			hashtextextended($1 || chr(31) || $2 || chr(31) || $3, 0)
+		)`
+
 // marshalPlaybackSession removes NUL code points from every nested string in
 // the JSON document. PostgreSQL JSONB rejects U+0000 even when Go's encoder
 // represents it as \u0000. Escaped literal text (\\u0000) remains unchanged.
@@ -218,8 +225,14 @@ func (d *DurableCompatPlaybackStore) replaceUnstartedNegotiation(
 
 	var removed []string
 	if session.CompatToken != "" && session.ClientDeviceID != "" && session.RouteItemID != "" {
-		scope := session.CompatToken + "\x00" + session.ClientDeviceID + "\x00" + session.RouteItemID
-		if _, err := tx.Exec(ctx, `SELECT pg_advisory_xact_lock(hashtextextended($1, 0))`, scope); err != nil {
+		// Join the lock key inside PostgreSQL. A Go-side NUL delimiter cannot
+		// be bound as text: PostgreSQL rejects U+0000 (SQLSTATE 22021), the
+		// transaction aborts, and the negotiated session stays cache-only.
+		if _, err := tx.Exec(ctx, compatNegotiationLockSQL,
+			stripCompatNUL(session.CompatToken),
+			stripCompatNUL(session.ClientDeviceID),
+			stripCompatNUL(session.RouteItemID),
+		); err != nil {
 			return nil, err
 		}
 		rows, err := tx.Query(ctx, `

internal/jellycompat/playback_sessions_postgres_test.go

@@ -5,6 +5,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"os"
+	"strings"
 	"testing"
 	"time"
 
@@ -13,6 +14,15 @@ import (
 	"github.com/jackc/pgx/v5/pgxpool"
 )
 
+func TestCompatNegotiationLockSQLDoesNotBindNULDelimiter(t *testing.T) {
+	if strings.Contains(compatNegotiationLockSQL, "\x00") {
+		t.Fatal("advisory lock SQL must not embed a NUL delimiter")
+	}
+	if !strings.Contains(compatNegotiationLockSQL, "chr(31)") {
+		t.Fatal("advisory lock SQL should join key parts with chr(31) inside PostgreSQL")
+	}
+}
+
 func TestMarshalPlaybackSessionStripsNestedNUL(t *testing.T) {
 	wantLiteral := `literal\u0000text`
 	data, err := marshalPlaybackSession(PlaybackSession{