TaskResponse declared created_at and updated_at as str, but both are
timestamp columns and psycopg2 returns datetime objects. Pydantic
rejected every response, so the endpoint raised ResponseValidationError
after the INSERT had already committed.
Every task creation therefore looked like a failure, and the natural
retry failed again with a genuine duplicate-key violation, making it
appear the first attempt had done nothing.
Declaring them as datetime leaves the JSON on the wire unchanged
(FastAPI serialises to ISO 8601) and matches what GET /tasks/{task_name}
already returned.
Co-Authored-By: Claude <noreply@anthropic.com>