fix(cookbook): locate cookbook_state.json via DATA_DIR, not hardcoded /app/data (#3332)

Three call sites hardcoded Path("/app/data/cookbook_state.json"), which only
exists in Docker; on a native run the real path is <repo>/data, so the state
file looked missing and cookbook serve-state was silently ignored. Two others
used os.environ.get("DATA_DIR", "data") (a relative fallback, since DATA_DIR is
never set as an env var). Route all five through core.constants.DATA_DIR so the
path is consistent and absolute on both Docker and native.

Part of #3331.

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

src/builtin_actions.py

@@ -12,7 +12,7 @@ from typing import Tuple
 
 from src.auth_helpers import owner_filter
 from core.platform_compat import IS_WINDOWS, find_bash
-from core.constants import internal_api_base
+from core.constants import DATA_DIR, internal_api_base
 
 logger = logging.getLogger(__name__)
 
@@ -2043,7 +2043,7 @@ async def action_cookbook_serve(
     except Exception:
         end_after_min = 0
 
-    state_path = Path("/app/data/cookbook_state.json")
+    state_path = Path(DATA_DIR) / "cookbook_state.json"
     try:
         state = json.loads(state_path.read_text(encoding="utf-8")) if state_path.exists() else {}
     except Exception:

src/cookbook_serve_lifecycle.py

@@ -19,7 +19,7 @@ import time
 from pathlib import Path
 
 import httpx
-from core.constants import internal_api_base
+from core.constants import DATA_DIR, internal_api_base
 
 logger = logging.getLogger(__name__)
 
@@ -130,7 +130,7 @@ async def _stop_serve(session_id: str, remote_host: str = "", ssh_port: str = ""
 
 
 async def _tick() -> None:
-    state_path = Path("/app/data/cookbook_state.json")
+    state_path = Path(DATA_DIR) / "cookbook_state.json"
     if not state_path.exists():
         return
     try: