Phase 179 Task 1: Modular separation for single responsibility
Changes:
- NEW: carrier_update_emitter.rs (416 lines)
- emit_carrier_update() function + 6 unit tests
- Focused module for UpdateExpr → JoinInst conversion
- REDUCED: loop_with_break_minimal.rs (998→597 lines, -401 lines)
- Removed emit_carrier_update() and carrier_update_tests module
- Now imports from carrier_update_emitter
- UPDATED: mod.rs - added carrier_update_emitter module
Benefits:
- Single responsibility: carrier update emission isolated
- Reusability: can be used by Pattern 3, 4, and future patterns
- Testability: independent unit tests
- Maintainability: 40% size reduction in loop_with_break_minimal.rs
Note: Pre-existing test failure in test_pattern2_accepts_loop_param_only
is unrelated to this refactoring (test expects 1 var but gets 3 due to
literal "10" and "5" being counted as variables).
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