fix(cookbook): preserve state during lifecycle tick

Log malformed cookbook state and re-read fresh state before writing scheduled-stop mutations so concurrent UI changes are preserved.

src/cookbook_serve_lifecycle.py

@@ -136,7 +136,8 @@ async def _tick() -> None:
         return
     try:
         state = json.loads(state_path.read_text(encoding="utf-8"))
-    except Exception:
+    except Exception as e:
+        logger.warning("cookbook_serve_lifecycle: state file unreadable (%s), skipping tick", e)
         return
     tasks = state.get("tasks") or []
     now_ms = int(time.time() * 1000)
@@ -178,8 +179,26 @@ async def _tick() -> None:
     if stopped_any:
         try:
             from core.atomic_io import atomic_write_json
-            state["tasks"] = tasks
-            atomic_write_json(state_path, state)
+            # Re-read the state file so concurrent UI writes (task adds,
+            # status flips, config edits) are not silently overwritten.
+            # Apply only our stop mutations to the fresh snapshot.
+            try:
+                fresh = json.loads(state_path.read_text(encoding="utf-8"))
+                fresh_tasks = fresh.get("tasks") or []
+            except Exception:
+                fresh = state
+                fresh_tasks = tasks
+            stopped_sids = {sid for sid, _, _ in to_stop}
+            for ft in fresh_tasks:
+                if not isinstance(ft, dict):
+                    continue
+                ft_sid = ft.get("sessionId") or ft.get("id")
+                if ft_sid in stopped_sids:
+                    ft["status"] = "stopped"
+                    ft["_scheduledStopAtMs"] = None
+                    ft["_lastStatusFlipAt"] = now_ms
+            fresh["tasks"] = fresh_tasks
+            atomic_write_json(state_path, fresh)
         except Exception as e:
             logger.warning(f"cookbook_serve_lifecycle: state write failed: {e}")