Improve readability of stream_completion_with_tools (~1000 line function):
- Add deduplicate_tool_calls() helper with closure for previous-message check
- Add should_auto_continue() with AutoContinueReason enum for clearer control flow
- Replace inline deduplication loop with helper call (-19 lines)
- Replace complex auto-continue conditional with match on reason enum (-13 lines)
- Add section comments for major phases (State Init, Pre-loop, Main Loop, Auto-Continue, Post-Loop)
- Add comprehensive tests for new helpers
Net reduction: 82 deletions, behavior unchanged (172+ tests pass)
Agent: carmack
a09967eb27