feat(core): add auth-store module to read local auth data

Reads sid and deviceId from ~/.super-multica/auth.json for use by
tools that need authenticated API access.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

packages/core/src/hub/auth-store.ts

@@ -0,0 +1,34 @@
+import { readFileSync } from "node:fs";
+import { join } from "node:path";
+import { DATA_DIR } from "@multica/utils";
+
+const AUTH_FILE_PATH = join(DATA_DIR, "auth.json");
+
+export type LocalAuthData = { sid: string; deviceId: string };
+
+/**
+ * Read sid and deviceId from ~/.super-multica/auth.json.
+ * Returns null if the file is missing, unreadable, or incomplete.
+ */
+export function getLocalAuth(): LocalAuthData | null {
+  try {
+    const raw = readFileSync(AUTH_FILE_PATH, "utf8").trim();
+    if (!raw) return null;
+
+    const data = JSON.parse(raw);
+    if (
+      typeof data !== "object" ||
+      data === null ||
+      typeof data.sid !== "string" ||
+      !data.sid ||
+      typeof data.deviceId !== "string" ||
+      !data.deviceId
+    ) {
+      return null;
+    }
+
+    return { sid: data.sid, deviceId: data.deviceId };
+  } catch {
+    return null;
+  }
+}

packages/core/src/hub/index.ts

@@ -1,4 +1,5 @@
 export { Hub } from "./hub.js";
 export type { MessageSource, InboundMessageEvent } from "./hub.js";
 export { getHubId } from "./hub-identity.js";
+export { getLocalAuth, type LocalAuthData } from "./auth-store.js";
 export type { HubOptions } from "./types.js";