feat: Add slashcommand api

docs-site/docs/developer/llm-plugin-builder-guide.md

@@ -621,7 +621,7 @@ interface PluginApiCustomStreamRequest {
   label?: string;
 }
 
-type PluginApiActionSource = 'composerAction' | 'toolbarAction' | 'profileAction' | 'manual';
+type PluginApiActionSource = 'composerAction' | 'toolbarAction' | 'profileAction' | 'slashCommand' | 'manual';
 interface PluginApiActionContext {
   source: PluginApiActionSource;
   user: User | null;
@@ -821,6 +821,10 @@ interface TojuClientPluginApi {
     registerEmbedRenderer: (id: string, contribution: PluginApiEmbedRendererContribution) => TojuPluginDisposable;
     mountElement: (id: string, request: PluginApiDomMountRequest) => TojuPluginDisposable;
   };
+  readonly commands: {
+    register: (id: string, contribution: PluginApiSlashCommandContribution) => TojuPluginDisposable;
+    list: () => PluginApiSlashCommandContribution[];
+  };
 }
 ```
 
@@ -1178,6 +1182,8 @@ Capabilities:
 | `registerEmbedRenderer`  | `ui.embeds`          |
 | `mountElement`           | `ui.dom`             |
 
+For `/` slash commands, use `api.commands.register` (capability `ui.commands`). See the Slash Commands subsection below.
+
 Register side panel:
 
 ```js
@@ -1310,6 +1316,36 @@ context.subscriptions.push(
 
 `mountElement` tags the element with plugin ownership metadata, replaces duplicate mounts for the same plugin/id, and removes it on disposal/unload.
 
+### Slash Commands
+
+Capability: `commands.register` and `commands.list` both require `ui.commands`.
+
+Register `/` slash commands that appear in the chat composer's autocomplete menu. Set `scope: 'global'` (default) for commands available in chat servers and direct messages, or `scope: 'server'` for commands only offered while a chat server is active. Declare `options` to parse arguments into `context.args` (use `type: 'rest'` to capture all trailing text). The `run` callback receives a context with `source: 'slashCommand'`, the parsed `args`, the invoked `command` name, the raw `rawArgs`, and the current user/server/channel.
+
+```js
+context.subscriptions.push(
+  api.commands.register('announce', {
+    name: 'announce',
+    description: 'Post an announcement to the current channel',
+    icon: 'megaphone',
+    scope: 'server',
+    options: [{ name: 'message', type: 'rest', required: true }],
+    run: (slash) => api.messages.send(`Announcement: ${slash.args.message}`, slash.textChannel?.id)
+  })
+);
+
+context.subscriptions.push(
+  api.commands.register('shrug', {
+    name: 'shrug',
+    description: 'Append the shrug emoticon',
+    scope: 'global',
+    run: () => api.messages.send('shrug')
+  })
+);
+```
+
+A command with no `options` runs immediately when picked; a command with options fills `/name ` so the user can type arguments before sending. Slash input is never posted as a chat message; unmatched `/text` falls through as a normal message.
+
 ## Capability Cheat Sheet
 
 | API call group                                                                               | Capabilities                                                                    |
@@ -1351,6 +1387,7 @@ context.subscriptions.push(
 | `ui.registerChannelSection`                                                                  | `ui.channelsSection`                                                            |
 | `ui.registerEmbedRenderer`                                                                   | `ui.embeds`                                                                     |
 | `ui.mountElement`                                                                            | `ui.dom`                                                                        |
+| `commands.register`, `commands.list`                                                         | `ui.commands`                                                                   |
 
 ## Complete Example Plugin