Serialize supported Pydantic values before writing TinyDB traces

tests/test_persistence_serialization.py

@@ -0,0 +1,36 @@
+from datetime import datetime, timezone
+from typing import Set
+
+from fastapi.testclient import TestClient
+from great_ai import GreatAI
+from great_ai.context import get_context
+from pydantic import BaseModel
+
+
+class DatedInput(BaseModel):
+    when: datetime
+    tags: Set[int]
+
+
+def test_tinydb_persists_json_compatible_model_values(isolated_context: None) -> None:
+    @GreatAI.create
+    def predict(data: DatedInput) -> int:
+        return len(data.tags)
+
+    with TestClient(predict.app) as client:
+        response = client.post(
+            "/predict", json={"data": {"when": "2026-01-01T00:00:00Z", "tags": [1, 2]}}
+        )
+        assert response.status_code == 200
+        trace_id = response.json()["trace_id"]
+    database = get_context().tracing_database
+    trace = database.get(trace_id)
+    assert trace is not None
+    assert trace.output == 2
+    trace.feedback = {"when": datetime(2026, 1, 1, tzinfo=timezone.utc)}
+    database.update(trace_id, trace)
+    updated = database.get(trace_id)
+    assert updated is not None
+    assert updated.feedback == {"when": "2026-01-01T00:00:00Z"}
+    database.save_batch([trace.model_copy(update={"trace_id": "batch"})])
+    assert database.get("batch") is not None