fix(python-client): async=true was silently ignored on retain calls

The hand-written client wrapper passed `async_=retain_async` to
RetainRequest, but the generated Pydantic model uses `var_async` as the
Python field name (with `alias="async"`). The `async_` kwarg didn't
match either the field name or the alias, so Pydantic silently ignored
it — every retain call ran synchronously regardless of the flag.

This has been broken since the client was first introduced (6073ac4f),
not a regression.

Also adds unit tests that verify the async field serializes correctly
in the request JSON, preventing future regressions.

hindsight-clients/python/hindsight_client/hindsight_client.py

@@ -204,7 +204,7 @@ class Hindsight:
 
         request_obj = retain_request.RetainRequest(
             items=memory_items,
-            async_=retain_async,
+            var_async=retain_async,
             document_tags=document_tags,
         )
 
@@ -618,7 +618,7 @@ class Hindsight:
 
         request_obj = retain_request.RetainRequest(
             items=memory_items,
-            async_=retain_async,
+            var_async=retain_async,
             document_tags=document_tags,
         )
 

hindsight-clients/python/tests/test_retain_request_async.py

@@ -0,0 +1,42 @@
+"""
+Test that RetainRequest correctly serializes the async field.
+
+Regression test for a bug where the client passed async_=True (invalid kwarg)
+instead of var_async=True, causing async mode to be silently ignored.
+"""
+
+from hindsight_client_api.models.memory_item import MemoryItem
+from hindsight_client_api.models.retain_request import RetainRequest
+
+
+def _make_item():
+    return MemoryItem(content="test content")
+
+
+def test_retain_request_async_true_serialized():
+    """var_async=True must appear as 'async': True in the serialized dict."""
+    req = RetainRequest(items=[_make_item()], var_async=True)
+    d = req.to_dict()
+    assert d["async"] is True
+
+
+def test_retain_request_async_false_serialized():
+    """var_async=False (default) must appear as 'async': False."""
+    req = RetainRequest(items=[_make_item()], var_async=False)
+    d = req.to_dict()
+    assert d["async"] is False
+
+
+def test_retain_request_default_is_sync():
+    """Omitting var_async should default to synchronous (async=False)."""
+    req = RetainRequest(items=[_make_item()])
+    d = req.to_dict()
+    assert d["async"] is False
+
+
+def test_retain_request_async_json_roundtrip():
+    """async=True must survive a JSON serialization roundtrip."""
+    req = RetainRequest(items=[_make_item()], var_async=True)
+    json_str = req.to_json()
+    restored = RetainRequest.from_json(json_str)
+    assert restored.var_async is True