feat(discord): add set-presence action for bot activity and status

Bridge the agent tools layer to the Discord gateway WebSocket via a new
gateway registry, allowing agents to set the bot's activity and online
status. Supports playing, streaming, listening, watching, custom, and
competing activity types. Custom type uses activityState as the sidebar
text; other types show activityName in the sidebar and activityState in
the flyout. Opt-in via channels.discord.actions.presence (default false).

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/agents/tools/message-tool.ts

@@ -193,6 +193,36 @@ function buildGatewaySchema() {
   };
 }
 
+function buildPresenceSchema() {
+  return {
+    activityType: Type.Optional(
+      Type.String({
+        description: "Activity type: playing, streaming, listening, watching, competing, custom.",
+      }),
+    ),
+    activityName: Type.Optional(
+      Type.String({
+        description: "Activity name shown in sidebar (e.g. 'with fire'). Ignored for custom type.",
+      }),
+    ),
+    activityUrl: Type.Optional(
+      Type.String({
+        description:
+          "Streaming URL (Twitch or YouTube). Only used with streaming type; may not render for bots.",
+      }),
+    ),
+    activityState: Type.Optional(
+      Type.String({
+        description:
+          "State text. For custom type this is the status text; for others it shows in the flyout.",
+      }),
+    ),
+    status: Type.Optional(
+      Type.String({ description: "Bot status: online, dnd, idle, invisible." }),
+    ),
+  };
+}
+
 function buildChannelManagementSchema() {
   return {
     name: Type.Optional(Type.String()),
@@ -225,6 +255,7 @@ function buildMessageToolSchemaProps(options: { includeButtons: boolean; include
     ...buildModerationSchema(),
     ...buildGatewaySchema(),
     ...buildChannelManagementSchema(),
+    ...buildPresenceSchema(),
   };
 }