Increase test coverage for Automata state machine

[fogfish]

Problem: Complex state machine logic lacks comprehensive tests.

Required Changes:

1. Create agent/automata_test.go
2. Test all phase transitions:
   • ASK → RETURN
   • ASK → REFINE → ASK
   • ASK → RETRY → ASK
   • ASK → ABORT
3. Test edge cases:
   • Max epochs reached
   • Decoder error vs feedback
   • Memory full
   • LLM error handling
4. Test multi-turn conversations
5. Aim for >80% coverage of Automata.Prompt()

Estimated Effort: 4 hours
Skills Required: Testing, state machine understanding