Persist agent chat sessions and protect manual titles

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

src/conversations/stateStore.ts

@@ -0,0 +1,41 @@
+import { join } from "node:path";
+
+import { config } from "../config.js";
+import {
+  atomicWriteJson,
+  ensureDirectory,
+  readJsonFile,
+  removeFileIfExists,
+} from "../utils/fileStore.js";
+
+export type ConversationStateRecord = {
+  sessionId: string;
+  isTitleManuallyEdited?: boolean;
+  messages: unknown[];
+  branchGroups: unknown[];
+};
+
+export class ConversationStateStore {
+  constructor(private readonly baseDir = config.CONVERSATION_STATE_STORAGE_DIR) {}
+
+  async initialize() {
+    await ensureDirectory(this.baseDir);
+  }
+
+  async read(sessionScopeKey: string) {
+    return await readJsonFile<ConversationStateRecord>(this.filePath(sessionScopeKey));
+  }
+
+  async write(sessionScopeKey: string, state: ConversationStateRecord) {
+    await atomicWriteJson(this.filePath(sessionScopeKey), state);
+    return state;
+  }
+
+  async remove(sessionScopeKey: string) {
+    await removeFileIfExists(this.filePath(sessionScopeKey));
+  }
+
+  private filePath(sessionScopeKey: string) {
+    return join(this.baseDir, `${sessionScopeKey}.json`);
+  }
+}