docs: 把「业务语义归插件、联动走事件总线」补进 OVERVIEW 与 PLUGIN_DEV

上一提交只在 ARCHITECTURE 里记了终端归属。本次把这条**通用原则**补到另外两份
文档，避免只读 OVERVIEW / 插件开发指南的人仍旧按旧直觉写代码。

## OVERVIEW（中英）

设计要点新增一条「业务语义留在插件层」：内核不定义业务对象（终端、命令历史、
设备状态、媒体库都是插件域）。以终端为例说明：PTY/生命周期/输出缓冲归
agentcli，WebUI/CLI 订阅总线自攒视图，内核只提供事件总线与注册面 —— 新增一类
能力不需要改内核，也不会在核心里堆出第二套业务真相。

## PLUGIN_DEV（中英）

PluginSDK 章节新增「与其它插件联动 — 走事件总线，不要依赖内核内部组件」：
- 代码示例：订阅 terminal_output + tool_call 自己攒视图
- 两条稳定事件表（谁发布、用途）
- ★ 外部插件只能订阅、不能发布（Publish 属 withheld 能力），所以「能力所有者
  需要广播状态」的插件必须内置（agentcli 即此例）
- 指向 internal/pluginview 作为参考实现，并写明「视图不是权威、晚启动会缺早期
  事件」

一个准确性修正：公开 SDK **没有** EventTerminalOutput 常量（属内核内部事件
类型），所以示例里外部插件用 sdk.EventType("terminal_output") 字符串订阅，
并注明内置插件可用 internal sdk 常量 —— 避免文档给出编不过的示例。

验证：四份文档代码围栏配对（74/74、0/0）；仅文档改动，无代码影响。

assets/docs/en/OVERVIEW.md

@@ -18,6 +18,15 @@ Core architecture: a long-running kernel process (`homed`) that connects to vari
 
 The significance lies in clear responsibility boundaries: the kernel focuses on orchestration and memory management, while plugins handle IO implementation — the two are not coupled.
 
+**Business semantics stay in plugins** — the kernel does not define business
+objects: terminals, command history, device state and media libraries all belong to
+the plugin domain. Take terminals: the PTY, session lifecycle and output buffering
+all live in `agentcli`; when WebUI or CLI needs a terminal panel it **subscribes to
+the event bus** (`EventTerminalOutput` + `EventToolCall`) and builds its own view
+instead of reading a state component inside the kernel. The kernel offers only the
+event bus and the plugin registration surface — adding a new capability does not
+require touching the kernel, and no second version of business truth accumulates there.
+
 **Three-Layer Memory Architecture** — Manages information retention across long agent runtimes through a tiered storage strategy:
 - **Context Layer**: In-memory pretrained word embedding scored event window (StaticEmbedder word vectors → CosineSimilarity, TF-IDF fallback), maintains recent context in real-time, low-relevance events automatically sink to the next layer
 - **Document Layer**: JSON files + TF-IDF vector-indexed temporary memory, supports explicit submission and implicit archival, cold data distills to Graph

assets/docs/en/PLUGIN_DEV.md

@@ -460,6 +460,45 @@ unsub := s.Events().Subscribe(sdk.EventToolCall, func(evt *sdk.Event) {
 defer unsub()
 ```
 
+#### Inter-plugin Integration — Use the Event Bus, Not Kernel Components
+
+The kernel carries no business-domain semantics (terminals, device state, media
+libraries all belong to plugins). Plugins that need to coordinate should therefore
+**subscribe to the event bus**, not read some state component inside the kernel —
+the latter creates a second copy of the truth and pushes business logic back into
+the kernel.
+
+```go
+// Panel-style plugins (WebUI/CLI): subscribe to terminal events, build a view
+// Note: terminal_output has no public constant yet (it is a kernel-internal event
+// type), so external plugins subscribe by string; built-in plugins can use the
+// internal SDK's EventTerminalOutput constant.
+unsubTerm := s.Events().Subscribe(sdk.EventType("terminal_output"), func(evt *sdk.Event) {
+    // evt.Payload: terminal_id / command / output / running
+})
+unsubTool := s.Events().Subscribe(sdk.EventToolCall, func(evt *sdk.Event) {
+    // evt.Payload: tool / args / status (cmd_run, terminal_create/close, ...)
+})
+defer unsubTerm()
+defer unsubTool()
+```
+
+The two stable events:
+
+| Event | Publisher | Purpose |
+|---|---|---|
+| `EventTerminalOutput` | agentcli | terminal output and lifecycle (create/close/timeout) |
+| `EventToolCall` | kernel | tool invocations (incl. `cmd_run`, `terminal_create/close`) |
+
+★ **External plugins can subscribe but cannot publish**: `Publish` is a withheld
+capability (`withheldCapabilities`), so a plugin that *owns* a capability and must
+broadcast its state (like agentcli publishing terminal events) has to be built-in.
+If your plugin is only a consumer, subscribing is enough.
+
+Reference implementation: `internal/pluginview` (the terminal view shared by WebUI
+and CLI). It shows how a view is assembled from events, and the boundary that the
+view is not authoritative — a late starter misses early events.
+
 #### Capability Access
 
 ```go