fix(crud): skip generated and read-only columns on insert and update

Read-merge-update wrote every model column back, so GENERATED ALWAYS
columns failed with SQLSTATE 428C9. Add a bun 'generated' tag option,
reflection.NonWritableColumns/RemoveNonWritableColumns, and apply them
in resolvespec, restheadspec, websocketspec, mqttspec, resolvemcp and
the nested CUD processor. Add ExcludeColumn to InsertQuery/UpdateQuery
for model-based writes.

pkg/reflection/model_utils.go

@@ -656,7 +656,7 @@ func isColumnWritableInType(typ reflect.Type, columnName string) (found bool, wr
 		// Check bun tag for scanonly
 		bunTag := field.Tag.Get("bun")
 		if bunTag != "" {
-			if isBunFieldScanOnly(bunTag) {
+			if isBunFieldScanOnly(bunTag) || isBunFieldGenerated(bunTag) {
 				return true, false
 			}
 		}
@@ -689,6 +689,70 @@ func isBunFieldScanOnly(tag string) bool {
 	return false
 }
 
+// isBunFieldGenerated checks if a bun tag marks the column as database-generated
+// (GENERATED ALWAYS AS ... STORED), which can be read but never written.
+// Example: "email_normalized,generated" -> true
+func isBunFieldGenerated(tag string) bool {
+	for _, part := range strings.Split(tag, ",") {
+		if strings.TrimSpace(part) == "generated" {
+			return true
+		}
+	}
+	return false
+}
+
+// RemoveNonWritableColumns deletes from values every key that maps to a
+// non-writable model column (bun scanonly/generated, gorm read-only). Used
+// before writing a read-merged record back with UPDATE ... SET.
+func RemoveNonWritableColumns(model any, values map[string]interface{}) {
+	for key := range values {
+		if !IsColumnWritable(model, key) {
+			delete(values, key)
+		}
+	}
+}
+
+// NonWritableColumns returns the column names of the model that cannot be
+// written (bun scanonly/generated, gorm read-only), including embedded structs.
+func NonWritableColumns(model any) []string {
+	t := reflect.TypeOf(model)
+	for t != nil && (t.Kind() == reflect.Pointer || t.Kind() == reflect.Slice || t.Kind() == reflect.Array) {
+		t = t.Elem()
+	}
+	if t == nil || t.Kind() != reflect.Struct {
+		return nil
+	}
+	var cols []string
+	collectNonWritable(t, &cols)
+	return cols
+}
+
+func collectNonWritable(typ reflect.Type, cols *[]string) {
+	for i := 0; i < typ.NumField(); i++ {
+		field := typ.Field(i)
+		if field.Anonymous {
+			ft := field.Type
+			if ft.Kind() == reflect.Pointer {
+				ft = ft.Elem()
+			}
+			if ft.Kind() == reflect.Struct {
+				collectNonWritable(ft, cols)
+				continue
+			}
+		}
+		bunTag, gormTag := field.Tag.Get("bun"), field.Tag.Get("gorm")
+		if bunTag == "-" || gormTag == "-" {
+			continue
+		}
+		if (bunTag != "" && (isBunFieldScanOnly(bunTag) || isBunFieldGenerated(bunTag))) ||
+			(gormTag != "" && isGormFieldReadOnly(gormTag)) {
+			if name := getColumnNameFromField(field); name != "" {
+				*cols = append(*cols, name)
+			}
+		}
+	}
+}
+
 // isGormFieldReadOnly checks if a gorm tag indicates the field is read-only
 // Examples:
 //   - "<-:false" -> true (no writes allowed)

pkg/reflection/model_utils_test.go

@@ -1920,3 +1920,46 @@ func TestMapToStruct_Errors(t *testing.T) {
 		})
 	}
 }
+
+func TestRemoveNonWritableColumns_Generated(t *testing.T) {
+	type m struct {
+		ID    int    `bun:"id,pk"`
+		Email string `bun:"email"`
+		Norm  string `bun:"email_normalized,generated"`
+		Scan  string `bun:"scan_col,scanonly"`
+	}
+	vals := map[string]interface{}{"id": 1, "email": "A", "email_normalized": "a", "scan_col": "x", "dynamic": 1}
+	RemoveNonWritableColumns(&m{}, vals)
+	if _, ok := vals["email_normalized"]; ok {
+		t.Error("generated column not removed")
+	}
+	if _, ok := vals["scan_col"]; ok {
+		t.Error("scanonly column not removed")
+	}
+	if len(vals) != 3 {
+		t.Errorf("unexpected keys: %v", vals)
+	}
+}
+
+func TestNonWritableColumns(t *testing.T) {
+	type base struct {
+		Created string `bun:"created_at,scanonly"`
+	}
+	type m struct {
+		base
+		ID    int    `bun:"id,pk"`
+		Email string `bun:"email"`
+		Norm  string `bun:"email_normalized,generated"`
+		Ro    string `gorm:"column:ro;->"`
+	}
+	got := NonWritableColumns(&m{})
+	want := map[string]bool{"created_at": true, "email_normalized": true, "ro": true}
+	if len(got) != len(want) {
+		t.Fatalf("got %v", got)
+	}
+	for _, c := range got {
+		if !want[c] {
+			t.Errorf("unexpected %s", c)
+		}
+	}
+}