refactor(desktop): ChatStore structured split + IDB persistence + stream cancel

Split monolithic chatStore.ts (908 lines) into 4 focused stores:
- chatStore.ts: facade layer, owns messages[], backward-compatible selectors
- conversationStore.ts: conversation CRUD, agent switching, IndexedDB persistence
- streamStore.ts: streaming orchestration, chat mode, suggestions
- messageStore.ts: token tracking

Key fixes from 3-round deep audit:
- C1: Fix Rust serde camelCase vs TS snake_case mismatch (toolStart/toolEnd/iterationStart)
- C2: Fix IDB async rehydration race with persist.hasHydrated() subscribe
- C3: Add sessionKey to partialize to survive page refresh
- H3: Fix IDB migration retry on failure (don't set migrated=true in catch)
- M3: Fix ToolCallStep deduplication (toolStart creates, toolEnd updates)
- M-NEW-2: Clear sessionKey on cancelStream

Also adds:
- Rust backend stream cancellation via AtomicBool + cancel_stream command
- IndexedDB storage adapter with one-time localStorage migration
- HMR cleanup for cross-store subscriptions

desktop/src/store/chat/conversationStore.ts

@@ -8,12 +8,10 @@
  */
 
 import { create } from 'zustand';
-import { persist } from 'zustand/middleware';
-import { generateRandomString } from '../lib/crypto-utils';
-import { createLogger } from '../lib/logger';
-import type { Message } from './chatStore';
-
-const log = createLogger('ConversationStore');
+import { persist, createJSONStorage } from 'zustand/middleware';
+import { generateRandomString } from '../../lib/crypto-utils';
+import { createIdbStorageAdapter } from '../../lib/idb-storage';
+import type { ChatMessage } from '../../types/chat';
 
 // ---------------------------------------------------------------------------
 // Types
@@ -22,7 +20,7 @@ const log = createLogger('ConversationStore');
 export interface Conversation {
   id: string;
   title: string;
-  messages: Message[];
+  messages: ChatMessage[];
   sessionKey: string | null;
   agentId: string | null;
   createdAt: Date;
@@ -45,9 +43,6 @@ export interface AgentProfileLike {
   role?: string;
 }
 
-// Re-export Message for internal use (avoids circular imports during migration)
-export type { Message };
-
 // ---------------------------------------------------------------------------
 // State interface
 // ---------------------------------------------------------------------------
@@ -61,10 +56,10 @@ export interface ConversationState {
   currentModel: string;
 
   // Actions
-  newConversation: (currentMessages: Message[]) => Conversation[];
-  switchConversation: (id: string, currentMessages: Message[]) => {
+  newConversation: (currentMessages: ChatMessage[]) => Conversation[];
+  switchConversation: (id: string, currentMessages: ChatMessage[]) => {
     conversations: Conversation[];
-    messages: Message[];
+    messages: ChatMessage[];
     sessionKey: string | null;
     currentAgent: Agent;
     currentConversationId: string;
@@ -74,10 +69,10 @@ export interface ConversationState {
     conversations: Conversation[];
     resetMessages: boolean;
   };
-  setCurrentAgent: (agent: Agent, currentMessages: Message[]) => {
+  setCurrentAgent: (agent: Agent, currentMessages: ChatMessage[]) => {
     conversations: Conversation[];
     currentAgent: Agent;
-    messages: Message[];
+    messages: ChatMessage[];
     sessionKey: string | null;
     isStreaming: boolean;
     currentConversationId: string | null;
@@ -87,7 +82,7 @@ export interface ConversationState {
     currentAgent: Agent;
   };
   setCurrentModel: (model: string) => void;
-  upsertActiveConversation: (currentMessages: Message[]) => Conversation[];
+  upsertActiveConversation: (currentMessages: ChatMessage[]) => Conversation[];
   getCurrentConversationId: () => string | null;
   getCurrentAgent: () => Agent | null;
   getSessionKey: () => string | null;
@@ -101,7 +96,7 @@ function generateConvId(): string {
   return `conv_${Date.now()}_${generateRandomString(4)}`;
 }
 
-function deriveTitle(messages: Message[]): string {
+function deriveTitle(messages: ChatMessage[]): string {
   const firstUser = messages.find(m => m.role === 'user');
   if (firstUser) {
     const text = firstUser.content.trim();
@@ -155,7 +150,7 @@ export function resolveAgentForConversation(agentId: string | null, agents: Agen
 
 function upsertActiveConversation(
   conversations: Conversation[],
-  messages: Message[],
+  messages: ChatMessage[],
   sessionKey: string | null,
   currentConversationId: string | null,
   currentAgent: Agent | null,
@@ -199,7 +194,7 @@ export const useConversationStore = create<ConversationState>()(
   sessionKey: null,
   currentModel: 'glm-4-flash',
 
-  newConversation: (currentMessages: Message[]) => {
+  newConversation: (currentMessages: ChatMessage[]) => {
     const state = get();
     const conversations = upsertActiveConversation(
       [...state.conversations], currentMessages, state.sessionKey,
@@ -213,7 +208,7 @@ export const useConversationStore = create<ConversationState>()(
     return conversations;
   },
 
-  switchConversation: (id: string, currentMessages: Message[]) => {
+  switchConversation: (id: string, currentMessages: ChatMessage[]) => {
     const state = get();
     const conversations = upsertActiveConversation(
       [...state.conversations], currentMessages, state.sessionKey,
@@ -251,7 +246,7 @@ export const useConversationStore = create<ConversationState>()(
     return { conversations, resetMessages };
   },
 
-  setCurrentAgent: (agent: Agent, currentMessages: Message[]) => {
+  setCurrentAgent: (agent: Agent, currentMessages: ChatMessage[]) => {
     const state = get();
     if (state.currentAgent?.id === agent.id) {
       set({ currentAgent: agent });
@@ -328,7 +323,7 @@ export const useConversationStore = create<ConversationState>()(
 
   setCurrentModel: (model: string) => set({ currentModel: model }),
 
-  upsertActiveConversation: (currentMessages: Message[]) => {
+  upsertActiveConversation: (currentMessages: ChatMessage[]) => {
     const state = get();
     const conversations = upsertActiveConversation(
       [...state.conversations], currentMessages, state.sessionKey,
@@ -344,11 +339,12 @@ export const useConversationStore = create<ConversationState>()(
 }),
     {
       name: 'zclaw-conversation-storage',
+      storage: createJSONStorage(() => createIdbStorageAdapter()),
       partialize: (state) => ({
         conversations: state.conversations,
         currentModel: state.currentModel,
-        currentAgentId: state.currentAgent?.id,
         currentConversationId: state.currentConversationId,
+        sessionKey: state.sessionKey,
       }),
       onRehydrateStorage: () => (state) => {
         if (state?.conversations) {