coder/fantasy now fails closed when Anthropic or OpenAI Responses
streams close before their provider terminal events instead of yielding
a successful finish.
This bumps the fantasy replacement to coder/fantasy#33 and teaches chat
error classification to treat those failures as retryable timeout errors
with explicit stream-closed messages.
<img width="875" height="311" alt="image"
src="https://github.com/user-attachments/assets/69c6f7b5-c885-46d2-a88b-b7a2b111bd55"
/>