fix(store): check ancestor $ref dialects during chain validation

_validate_chain_dialect seeded its reference walk from the selected type
only, so a cross-dialect gts:// $ref on an ancestor was accepted by
validate_instance_content and OP#12. Seed the walk from every type in the
chain so the whole chain plus its reference closure shares the root
dialect (spec 11.0/12), matching the Rust reference.

Signed-off-by: Artifizer <artifizer@gmail.com>

Author: Artifizer

gts/src/gts/store.py

@@ -502,6 +502,8 @@ def _validate_chain_dialect(
             return
         root_dialect = self._schema_dialect(root_content)
 
+        visited: set[str] = set()
+        queue: deque[tuple[str, dict[str, Any]]] = deque()
         for chain_id in chain_ids:
             entity = self.get(chain_id)
             content = (
@@ -521,15 +523,12 @@ def _validate_chain_dialect(
                         "$id hierarchy must use the root type's dialect"
                     )
                 self._validate_local_ref_dialects(content, chain_ids[0], root_dialect)
-
-        visited: set[str] = set()
-        queue: deque[tuple[str, dict[str, Any]]] = deque(
-            [(gts_id, transient_schema)] if transient_schema is not None else []
-        )
-        if not queue:
-            entity = self.get(gts_id)
-            if entity and isinstance(entity.content, dict):
-                queue.append((gts_id, entity.content))
+                # Seed the reference walk from every chain member, not just the
+                # leaf, so a cross-dialect gts:// $ref on an ancestor is caught
+                # even when the leaf does not reference it (spec §11.0/§12;
+                # matches the Rust reference which validates each related type in
+                # the closure).
+                queue.append((chain_id, content))
         while queue:
             current_id, content = queue.popleft()
             if current_id in visited:

tests/test_store_extra.py

@@ -452,6 +452,60 @@ def test_transitive_ref_dialect_mismatch_raises(self):
         with pytest.raises(ValueError, match="gts.x.test._.foreign.v1~"):
             store._validate_schema_chain("gts.x.test._.host.v1~")
 
+    def test_ancestor_ref_dialect_mismatch_raises(self):
+        # Issue C: the cross-dialect $ref lives on an ancestor; the descendant
+        # derives by re-declaration and references neither the ancestor nor the
+        # 2020-12 target. A leaf-only reference walk would accept it; walking the
+        # whole chain closure must reject it (OP#12 path).
+        foreign = _schema_entity(
+            "gts.x.test._.ancforeign.v1~",
+            {"$schema": "https://json-schema.org/draft/2020-12/schema"},
+        )
+        base = _schema_entity(
+            "gts.x.test._.ancbase.v1~",
+            {"properties": {"ext": {"$ref": "gts://gts.x.test._.ancforeign.v1~"}}},
+        )
+        child = _schema_entity(
+            "gts.x.test._.ancbase.v1~x.test._.ancchild.v1~",
+            {"properties": {"label": {"type": "string"}}},
+        )
+        store = GtsStore(reader=None)
+        store.register(foreign)
+        store.register(base)
+        store.register(child)
+
+        with pytest.raises(ValueError, match="gts.x.test._.ancforeign.v1~"):
+            store._validate_schema_chain(
+                "gts.x.test._.ancbase.v1~x.test._.ancchild.v1~"
+            )
+
+    def test_instance_content_rejects_ancestor_cross_dialect_ref(self):
+        # Issue C on the OP#6 instance path: validating an instance of the
+        # descendant must reject it because an ancestor references a schema of a
+        # different dialect.
+        foreign = _schema_entity(
+            "gts.x.test._.ancforeign2.v1~",
+            {"$schema": "https://json-schema.org/draft/2020-12/schema"},
+        )
+        base = _schema_entity(
+            "gts.x.test._.ancbase2.v1~",
+            {"properties": {"ext": {"$ref": "gts://gts.x.test._.ancforeign2.v1~"}}},
+        )
+        child = _schema_entity(
+            "gts.x.test._.ancbase2.v1~x.test._.ancchild2.v1~",
+            {"properties": {"label": {"type": "string"}}},
+        )
+        store = GtsStore(reader=None)
+        store.register(foreign)
+        store.register(base)
+        store.register(child)
+
+        with pytest.raises(ValueError, match="gts.x.test._.ancforeign2.v1~"):
+            store.validate_instance_content(
+                {"label": "ok"},
+                "gts.x.test._.ancbase2.v1~x.test._.ancchild2.v1~",
+            )
+
     def test_trait_resource_dialect_mismatch_raises(self):
         schema_id = "gts.x.test._.trait_resource.v1~"
         schema = _schema_entity(