Centralize execution setting and session validation

internal/domain/session_test.go

@@ -7,10 +7,10 @@ import (
 
 func TestNormalizeSessionID(t *testing.T) {
 	tests := []struct {
-		name    string
-		raw     string
-		want    string
-		wantErr bool
+		name            string
+		raw             string
+		want            string
+		wantErrContains string
 	}{
 		{
 			name: "trims surrounding Unicode whitespace",
@@ -28,21 +28,24 @@ func TestNormalizeSessionID(t *testing.T) {
 			want: strings.Repeat("界", SessionIDMaxLength),
 		},
 		{
-			name:    "one Unicode code point over maximum is rejected",
-			raw:     strings.Repeat("界", SessionIDMaxLength+1),
-			wantErr: true,
+			name:            "one Unicode code point over maximum is rejected",
+			raw:             strings.Repeat("界", SessionIDMaxLength+1),
+			wantErrContains: "exceeds maximum",
 		},
+		{name: "invalid UTF-8 before valid content", raw: string([]byte{0xff}) + "session", wantErrContains: "valid UTF-8"},
+		{name: "invalid UTF-8 within valid content", raw: "ses" + string([]byte{0xff}) + "sion", wantErrContains: "valid UTF-8"},
+		{name: "invalid UTF-8 after valid content", raw: "session" + string([]byte{0xff}), wantErrContains: "valid UTF-8"},
 	}
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
 			got, err := NormalizeSessionID(tt.raw)
-			if tt.wantErr {
+			if tt.wantErrContains != "" {
 				if err == nil {
 					t.Fatal("expected normalization error")
 				}
-				if !strings.Contains(err.Error(), "exceeds maximum") {
-					t.Fatalf("expected useful length diagnostic, got %v", err)
+				if !strings.Contains(err.Error(), tt.wantErrContains) {
+					t.Fatalf("expected diagnostic containing %q, got %v", tt.wantErrContains, err)
 				}
 				return
 			}