diff --git a/CLAUDE.md b/CLAUDE.md
index 2452574d..a9112e6e 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -232,6 +232,7 @@ After running, the Coding Agent should:
 
 - **`SMC_DATA_DIR=~/.super-multica-e2e`** isolates E2E test sessions from dev (`~/.super-multica-dev`) and production (`~/.super-multica`) data. Always set this.
 - **`MULTICA_API_URL=https://api-dev.copilothub.ai`** is required for `web_search` and `data` tools. Without it, these tools fail with `MULTICA_API_URL is required`.
+- **Auth for `web_search`/`data`**: These tools need dev backend auth. The auth store auto-falls back to `~/.super-multica-dev/auth.json`. If missing, run `pnpm dev:local` first and log in through the Desktop app.
 - Default provider is `kimi-coding`. Override with `--provider`.
 - Run-log and session data are at `~/.super-multica-e2e/sessions/{sessionId}/`
 - Detailed guide with feature-specific test playbooks: `docs/e2e-testing-guide.md`
diff --git a/docs/e2e-testing-guide.md b/docs/e2e-testing-guide.md
index e25eff0d..3892f5b7 100644
--- a/docs/e2e-testing-guide.md
+++ b/docs/e2e-testing-guide.md
@@ -23,6 +23,7 @@ This approach is superior to static assertions because:
 3. **Default provider**: `kimi-coding` (Kimi Code, free tier available). Can override with `--provider`
 4. **`MULTICA_API_URL`**: Required for `web_search` and `data` tools. Set to `https://api-dev.copilothub.ai` for dev environment. Without this, web search and financial data tools will fail with `MULTICA_API_URL is required`
 5. **`SMC_DATA_DIR`**: Set to `~/.super-multica-e2e` to isolate E2E test sessions from dev (`~/.super-multica-dev`) and production (`~/.super-multica`) data. Without this, test sessions pollute the production sessions directory
+6. **Dev auth for `web_search`/`data` tools**: These tools authenticate via `auth.json` (session ID + device ID). The auth store automatically falls back to `~/.super-multica-dev/auth.json` when the E2E data dir has no auth. If `~/.super-multica-dev/auth.json` doesn't exist, run `pnpm dev:local` first and log in through the Desktop app to create it
 
 ## Running a Test
 
diff --git a/packages/core/src/hub/api-client.ts b/packages/core/src/hub/api-client.ts
index c3254463..d739cc9d 100644
--- a/packages/core/src/hub/api-client.ts
+++ b/packages/core/src/hub/api-client.ts
@@ -19,7 +19,7 @@ export function getAuthHeaders(context?: string): Record<string, string> {
   if (!auth) {
     const suffix = context ? ` ${context}` : "";
     throw new Error(
-      `Not logged in. Please sign in via the Desktop app${suffix}.`,
+      `Not logged in${suffix}. Sign in via the Desktop app, or run pnpm dev:local and log in there.`,
     );
   }
   return {
diff --git a/packages/core/src/hub/auth-store.ts b/packages/core/src/hub/auth-store.ts
index ff2342ba..23c88c41 100644
--- a/packages/core/src/hub/auth-store.ts
+++ b/packages/core/src/hub/auth-store.ts
@@ -1,18 +1,16 @@
 import { readFileSync } from "node:fs";
+import { homedir } from "node:os";
 import { join } from "node:path";
 import { DATA_DIR } from "@multica/utils";
 
 const AUTH_FILE_PATH = join(DATA_DIR, "auth.json");
+const DEV_AUTH_FILE_PATH = join(homedir(), ".super-multica-dev", "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 {
+function tryReadAuth(filePath: string): LocalAuthData | null {
   try {
-    const raw = readFileSync(AUTH_FILE_PATH, "utf8").trim();
+    const raw = readFileSync(filePath, "utf8").trim();
     if (!raw) return null;
 
     const data = JSON.parse(raw);
@@ -32,3 +30,26 @@ export function getLocalAuth(): LocalAuthData | null {
     return null;
   }
 }
+
+/**
+ * Read sid and deviceId from auth.json.
+ *
+ * Lookup order:
+ * 1. {DATA_DIR}/auth.json (current data dir, respects SMC_DATA_DIR)
+ * 2. ~/.super-multica-dev/auth.json (dev environment fallback —
+ *    allows E2E tests and other custom SMC_DATA_DIR setups to
+ *    share the dev auth created by `pnpm dev:local`)
+ *
+ * Returns null if no valid auth is found.
+ */
+export function getLocalAuth(): LocalAuthData | null {
+  const primary = tryReadAuth(AUTH_FILE_PATH);
+  if (primary) return primary;
+
+  // Fallback to dev auth when using a custom data dir (e.g. E2E tests)
+  if (AUTH_FILE_PATH !== DEV_AUTH_FILE_PATH) {
+    return tryReadAuth(DEV_AUTH_FILE_PATH);
+  }
+
+  return null;
+}