docs: update output channel interface (payload/meta/type) in SDK docs

README.md

@@ -53,6 +53,11 @@ sdk.RegisterStage(StageBeforeToolcall, myHandler, StageScopeOwnTools)
 sdk.RegisterOutputChannel("my-channel", CapText|CapFile, "通道描述", handler)
 ```
 
+handler 接收三个参数：
+- `payload` (string) — 消息载荷。`type=text` 时直接填文字，`type=file/image` 时填 URL
+- `meta` (string) — 可选的 JSON 路由元数据（如 `{"group_id":123,"user_id":456}`）
+- `type` (string) — 载荷类型，枚举值见下
+
 能力标志位：
 
 | 标志 | 值 | 说明 |
@@ -63,6 +68,15 @@ sdk.RegisterOutputChannel("my-channel", CapText|CapFile, "通道描述", handler
 | `CapAudio` | 8 | 音频输出 |
 | `CapStructured` | 16 | 结构化数据输出 |
 
+type 枚举值：
+
+| 值 | 说明 |
+|----|------|
+| `text` | 纯文本 |
+| `voice` / `audio` | 语音 |
+| `image` | 图片 |
+| `file` | 文件 |
+
 ### IOInjector 通道路由
 
 | 方法 | 说明 |

README_EN.md

@@ -53,6 +53,11 @@ sdk.RegisterStage(StageBeforeToolcall, myHandler, StageScopeOwnTools)
 sdk.RegisterOutputChannel("my-channel", CapText|CapFile, "channel description", handler)
 ```
 
+The handler receives three arguments:
+- `payload` (string) — message content. For `type=text` it's plain text, for `type=file/image` it's a URL
+- `meta` (string) — optional JSON routing metadata (e.g. `{"group_id":123,"user_id":456}`)
+- `type` (string) — content type enum (see below)
+
 Capability flags:
 
 | Flag | Value | Description |
@@ -63,6 +68,15 @@ Capability flags:
 | `CapAudio` | 8 | Audio output |
 | `CapStructured` | 16 | Structured data output |
 
+Type enum values:
+
+| Value | Description |
+|-------|-------------|
+| `text` | plain text |
+| `voice` / `audio` | audio/voice |
+| `image` | image |
+| `file` | file |
+
 ### IOInjector Channel Routing
 
 | Method | Description |

sdk/plugin.go

@@ -286,8 +286,8 @@ func (s *PluginSDK) RegisterPluginAPI(name string) error {
 // RegisterOutputChannel registers an output channel that the output_send tool can route to.
 // name: channel name (e.g. "qq", "webui")
 // caps: bitmask of supported output capabilities (CapText, CapFile, etc.)
-// desc: description of the channel and expected JSON format for content
+// desc: description of the channel, expected meta format, and type enum
-// handler: receives the content (JSON string) and returns result/error
+// handler: receives args map with keys: payload (string), type (string), meta (string|optional)
 func (s *PluginSDK) RegisterOutputChannel(name string, caps int, desc string, handler ToolHandler) error {
 	if s.regOutput != nil {
 		return s.regOutput(name, caps, desc, handler)