docs: Phase 138 - ReturnValueLowererBox SSOT documentation
Phase 138 Documentation:
- Created docs/development/current/main/phases/phase-138/README.md
- Goal: Extract return lowering to shared Box for SSOT
- SSOT: common/return_value_lowerer_box.rs
- Supported: Variable, Integer literal, Add expression (x + 2, 5 + 3)
- Implementation: New files, modified files, call sites
- Tests: 5 unit tests + all regressions PASS
- Architecture Impact: Code reduction, maintainability, testability
- Phase 139 準備: Next step clearly indicated (post_if_post_k.rs unification)
10-Now.md Updates:
- Added Phase 138 entry (ReturnValueLowererBox SSOT)
- Implementation details and test coverage
- Design decision: Phase 138 P0 migrated loop paths only
- Link to Phase 138 README
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Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>
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