fix(#40): remove illegal literal default on TEXT column image_url

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

server/app/goauto/migrations/migrate_test.go

@@ -3,6 +3,7 @@ package migrations_test
 import (
 	"fmt"
 	"reflect"
+	"regexp"
 	"strings"
 	"sync"
 	"testing"
@@ -333,3 +334,28 @@ func TestShopeeProductSalePriceMustNotBeNegative(t *testing.T) {
 		t.Fatal("negative sale price was accepted")
 	}
 }
+
+// MySQL rejects a literal DEFAULT clause on TEXT/BLOB/JSON columns
+// ("BLOB, TEXT, GEOMETRY or JSON column '...' can't have a default value").
+// SQLite does not enforce this, so the SQLite-backed tests in this file never
+// catch it; ShopeeProduct.ImageURL hit exactly this error against a live
+// MySQL 8.4 database before this test was added. This scans every model field
+// via reflection instead of requiring a MySQL connection.
+func TestMySQLTextJSONBlobColumnsHaveNoLiteralDefault(t *testing.T) {
+	modelTypes := []any{
+		&models.AgentDevice{}, &models.PDDProduct{}, &models.CollectionRule{}, &models.CollectionTask{},
+		&models.CollectionDimension{}, &models.CollectionDimensionValue{}, &models.CollectionColorPrice{},
+		&models.CollectionSKU{}, &models.CollectionSKUValue{}, &models.ShopeeProduct{},
+	}
+	typePattern := regexp.MustCompile(`type:(text|json|blob)`)
+	for _, model := range modelTypes {
+		value := reflect.TypeOf(model).Elem()
+		for i := 0; i < value.NumField(); i++ {
+			tag := value.Field(i).Tag.Get("gorm")
+			if typePattern.MatchString(strings.ToLower(tag)) && strings.Contains(tag, "default:") {
+				t.Errorf("%s.%s: TEXT/JSON/BLOB column must not carry a literal gorm default tag (MySQL rejects it): %s",
+					value.Name(), value.Field(i).Name, tag)
+			}
+		}
+	}
+}

server/app/goauto/models/schema.go

@@ -252,7 +252,10 @@ type ShopeeProduct struct {
 	// ImageURL holds the SYB-provided reference image URL. It is written by the
 	// #41 import and may be overridden manually; the product domain never joins
 	// syb_products at read time.
-	ImageURL string `json:"imageUrl" gorm:"type:text;not null;default:''"`
+	// MySQL rejects a literal DEFAULT on TEXT/BLOB/JSON columns, so this stays
+	// NOT NULL without a DB-level default; Go's zero value ("") is inserted
+	// explicitly on every create, which satisfies NOT NULL without needing one.
+	ImageURL string `json:"imageUrl" gorm:"type:text;not null"`
 	// SalePriceCent is the reference selling price in integer cents, consistent
 	// with the priceCent convention from #31. It is the value seen at the latest
 	// import or manual edit, not an authoritative transaction price.