fix(model): return string from JSON column Valuers for pg simple protocol

With PrepareStmt disabled, PostgreSQL queries run over pgx's simple
protocol, which encodes every []byte parameter as a bytea hex literal
('\x...'). driver.Valuer implementations returning []byte from
json.Marshal therefore fail json-column writes with SQLSTATE 22P02
(reported on the channels UPDATE path via ChannelInfo).

Reproduced against a live PostgreSQL 16: []byte Valuer into a json
column fails under simple protocol, string succeeds; []byte into a
text column silently stores the hex literal (no such path exists in
the repo today — audited all Valuers, json.RawMessage fields, and raw
SQL call sites).

- ChannelInfo, Properties, TaskPrivateData, JSONValue Value() now
  return string; zero-value nil semantics unchanged. Task.Data
  (bare json.RawMessage) is unaffected — database/sql's default
  converter already passes it as expected.
- Their Scan() counterparts now accept both []byte and string via a
  shared jsonScanBytes helper: SQLite returns string for these columns
  once Value() emits string, and the old []byte-only assertions
  silently zeroed the field (caught by the model test suite).
- Add regression tests locking both contracts: json-column Valuers
  must return string (or nil for zero values), Scanners must accept
  []byte and string.

Verified end-to-end against PostgreSQL 16 with the real model types:
Channel create/update/read-back, Task json fields, PrefillGroup items.

model/channel.go

@@ -162,14 +162,19 @@ func ApplyChannelGroupFilter(query *gorm.DB, group string) *gorm.DB {
 }
 
 // Value implements driver.Valuer interface
+// 必须返回 string 而非 []byte:PG simple protocol 下 []byte 参数按 bytea
+// 编码,写 json 列会触发 SQLSTATE 22P02。
 func (c ChannelInfo) Value() (driver.Value, error) {
-	return common.Marshal(&c)
+	b, err := common.Marshal(&c)
+	if err != nil {
+		return nil, err
+	}
+	return string(b), nil
 }
 
 // Scan implements sql.Scanner interface
 func (c *ChannelInfo) Scan(value interface{}) error {
-	bytesValue, _ := value.([]byte)
+	return common.Unmarshal(jsonScanBytes(value), c)
-	return common.Unmarshal(bytesValue, c)
 }
 
 func (channel *Channel) GetKeys() []string {

model/json_column_test.go

@@ -0,0 +1,94 @@
+package model
+
+import (
+	"database/sql/driver"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+// 保护契约:PostgreSQL 走 simple protocol(PrepareStmt 关闭)时,driver.Valuer
+// 返回 []byte 会被 pgx 按 bytea 十六进制字面量编码,写入 json 列触发
+// SQLSTATE 22P02。所有 json 列的 Value() 必须返回 string(或 nil)。
+func TestJSONColumnValuersReturnString(t *testing.T) {
+	testCases := []struct {
+		name   string
+		valuer driver.Valuer
+		want   string
+	}{
+		{
+			name:   "ChannelInfo",
+			valuer: ChannelInfo{IsMultiKey: true, MultiKeySize: 2},
+			want:   `{"is_multi_key":true,"multi_key_size":2,"multi_key_status_list":null,"multi_key_polling_index":0,"multi_key_mode":""}`,
+		},
+		{
+			name:   "Properties",
+			valuer: Properties{Input: "hello"},
+			want:   `{"input":"hello"}`,
+		},
+		{
+			name:   "TaskPrivateData",
+			valuer: TaskPrivateData{Key: "k"},
+			want:   `{"key":"k"}`,
+		},
+		{
+			name:   "JSONValue",
+			valuer: JSONValue(`[{"k":"v"}]`),
+			want:   `[{"k":"v"}]`,
+		},
+	}
+
+	for _, testCase := range testCases {
+		t.Run(testCase.name, func(t *testing.T) {
+			value, err := testCase.valuer.Value()
+			require.NoError(t, err)
+			str, ok := value.(string)
+			require.True(t, ok, "Value() must return string, got %T", value)
+			assert.JSONEq(t, testCase.want, str)
+		})
+	}
+}
+
+// 空值仍返回 nil,保持列的 NULL 语义。
+func TestJSONColumnValuersZeroValueIsNil(t *testing.T) {
+	for name, valuer := range map[string]driver.Valuer{
+		"Properties":      Properties{},
+		"TaskPrivateData": TaskPrivateData{},
+		"JSONValue":       JSONValue(nil),
+	} {
+		t.Run(name, func(t *testing.T) {
+			value, err := valuer.Value()
+			require.NoError(t, err)
+			assert.Nil(t, value)
+		})
+	}
+}
+
+// 保护契约:json 列的 Scan 必须同时接受 []byte 与 string——不同驱动/协议
+// 模式返回类型不同,静默丢弃 string 会把已有数据清零。
+func TestJSONColumnScannersAcceptStringAndBytes(t *testing.T) {
+	toInput := func(kind string, payload string) interface{} {
+		if kind == "bytes" {
+			return []byte(payload)
+		}
+		return payload
+	}
+
+	for _, kind := range []string{"bytes", "string"} {
+		t.Run(kind, func(t *testing.T) {
+			var info ChannelInfo
+			require.NoError(t, info.Scan(toInput(kind, `{"is_multi_key":true,"multi_key_size":2}`)))
+			assert.True(t, info.IsMultiKey)
+			assert.Equal(t, 2, info.MultiKeySize)
+
+			var props Properties
+			require.NoError(t, props.Scan(toInput(kind, `{"input":"hello"}`)))
+			assert.Equal(t, "hello", props.Input)
+
+			var private TaskPrivateData
+			require.NoError(t, private.Scan(toInput(kind, `{"key":"k"}`)))
+			assert.Equal(t, "k", private.Key)
+		})
+	}
+}

model/main.go

@@ -27,6 +27,19 @@ var commonFalseVal string
 var logKeyCol string
 var logGroupCol string
 
+// jsonScanBytes 归一化 json 列的驱动返回值:不同驱动/协议模式下同一列可能
+// 以 []byte 或 string 返回,静默丢弃 string 会导致字段被清零而不报错。
+func jsonScanBytes(value interface{}) []byte {
+	switch v := value.(type) {
+	case []byte:
+		return v
+	case string:
+		return []byte(v)
+	default:
+		return nil
+	}
+}
+
 func initCol() {
 	// init common column names
 	if common.UsingMainDatabase(common.DatabaseTypePostgreSQL) {

model/prefill_group.go

@@ -20,11 +20,13 @@ import (
 type JSONValue json.RawMessage
 
 // Value 实现 driver.Valuer 接口，用于数据库写入
+// 必须返回 string 而非 []byte:PG simple protocol 下 []byte 按 bytea 编码,
+// 写 json 列会触发 SQLSTATE 22P02。
 func (j JSONValue) Value() (driver.Value, error) {
 	if j == nil {
 		return nil, nil
 	}
-	return []byte(j), nil
+	return string(j), nil
 }
 
 // Scan 实现 sql.Scanner 接口，兼容不同驱动返回的类型

model/task.go

@@ -87,7 +87,7 @@ type Properties struct {
 }
 
 func (m *Properties) Scan(val interface{}) error {
-	bytesValue, _ := val.([]byte)
+	bytesValue := jsonScanBytes(val)
 	if len(bytesValue) == 0 {
 		*m = Properties{}
 		return nil
@@ -99,7 +99,13 @@ func (m Properties) Value() (driver.Value, error) {
 	if m == (Properties{}) {
 		return nil, nil
 	}
-	return common.Marshal(m)
+	// 必须返回 string 而非 []byte:PG simple protocol 下 []byte 按 bytea 编码,
+	// 写 json 列会触发 SQLSTATE 22P02。
+	b, err := common.Marshal(m)
+	if err != nil {
+		return nil, err
+	}
+	return string(b), nil
 }
 
 type TaskPrivateData struct {
@@ -180,7 +186,7 @@ func GenerateTaskID() string {
 }
 
 func (p *TaskPrivateData) Scan(val interface{}) error {
-	bytesValue, _ := val.([]byte)
+	bytesValue := jsonScanBytes(val)
 	if len(bytesValue) == 0 {
 		return nil
 	}
@@ -191,7 +197,12 @@ func (p TaskPrivateData) Value() (driver.Value, error) {
 	if (p == TaskPrivateData{}) {
 		return nil, nil
 	}
-	return common.Marshal(p)
+	// 同 Properties.Value:string 避免 PG simple protocol 的 bytea 编码。
+	b, err := common.Marshal(p)
+	if err != nil {
+		return nil, err
+	}
+	return string(b), nil
 }
 
 // SyncTaskQueryParams 用于包含所有搜索条件的结构体，可以根据需求添加更多字段