fix(api): align zone content kind validation with model

Co-authored-by: Cursor <cursoragent@cursor.com>

src/models/zone.py

@@ -21,8 +21,8 @@ def _maybe_migrate_tab_json_to_zone():
 class Zone(Model):
     """Preset layout row (stored in ``db/zone.json``); legacy storage was ``tab.json`` / Tab.
 
-    Optional ``content_kind`` on a row: ``\"presets\"`` (preset tiles only) or ``\"sequences\"``
-    (sequence tiles only). Legacy rows without ``content_kind`` are inferred on load.
+    Optional legacy ``content_kind`` (``\"presets\"`` / ``\"sequences\"``) is kept for older data;
+    zones may hold both preset tiles and ``sequence_ids``.
     """
 
     def __init__(self):
@@ -95,13 +95,8 @@ class Zone(Model):
         return "presets"
 
     def _enforce_content_kind_invariants(self, doc):
-        """Presets-only zones hold no sequences; sequences-only hold no preset tiles."""
-        kind = self._normalized_content_kind(doc)
-        if kind == "presets":
-            doc["sequence_ids"] = []
-        elif kind == "sequences":
-            doc["presets"] = []
-            doc["presets_flat"] = []
+        """No-op: presets and sequences may coexist on one zone."""
+        _ = doc
 
     def create(self, name="", names=None, presets=None, group_ids=None, content_kind=None):
         next_id = self.get_next_id()
@@ -135,13 +130,7 @@ class Zone(Model):
         if id_str not in self:
             return False
         patch = dict(data) if isinstance(data, dict) else {}
-        doc = self[id_str]
-        locked_kind = self._normalized_content_kind(doc) or self._infer_content_kind(doc)
-        if "content_kind" in patch:
-            patch["content_kind"] = locked_kind
         self[id_str].update(patch)
-        if "content_kind" in patch:
-            self._enforce_content_kind_invariants(self[id_str])
         self.save()
         return True