feat: implement multi-message mode and shuffle mode features

- Add multi-message mode with start/end/prompt markers
- Implement turn order shuffling with /turn-shuffling command
- Add channel mode state management
- Update hooks to handle multi-message mode behavior
- Update plugin config with new markers
- Update TASKLIST.md with completed tasks

plugin/core/channel-modes.ts

@@ -0,0 +1,51 @@
+export type ChannelMode = "normal" | "multi-message";
+
+export type ChannelModesState = {
+  mode: ChannelMode;
+  shuffling: boolean;
+  lastShuffledAt?: number;
+};
+
+const channelStates = new Map<string, ChannelModesState>();
+
+export function getChannelState(channelId: string): ChannelModesState {
+  if (!channelStates.has(channelId)) {
+    channelStates.set(channelId, {
+      mode: "normal",
+      shuffling: false,
+    });
+  }
+  return channelStates.get(channelId)!;
+}
+
+export function enterMultiMessageMode(channelId: string): void {
+  const state = getChannelState(channelId);
+  state.mode = "multi-message";
+  channelStates.set(channelId, state);
+}
+
+export function exitMultiMessageMode(channelId: string): void {
+  const state = getChannelState(channelId);
+  state.mode = "normal";
+  channelStates.set(channelId, state);
+}
+
+export function isMultiMessageMode(channelId: string): boolean {
+  return getChannelState(channelId).mode === "multi-message";
+}
+
+export function setChannelShuffling(channelId: string, enabled: boolean): void {
+  const state = getChannelState(channelId);
+  state.shuffling = enabled;
+  channelStates.set(channelId, state);
+}
+
+export function getChannelShuffling(channelId: string): boolean {
+  return getChannelState(channelId).shuffling;
+}
+
+export function markLastShuffled(channelId: string): void {
+  const state = getChannelState(channelId);
+  state.lastShuffledAt = Date.now();
+  channelStates.set(channelId, state);
+}