Builder pattern for JoinInlineBoundary construction, reduces field manipulation scattering.
# Changes
- NEW: src/mir/join_ir/lowering/inline_boundary_builder.rs (165 lines)
- JoinInlineBoundaryBuilder with 7 fluent methods
- Complete unit test coverage (4 tests)
- MODIFIED: src/mir/join_ir/lowering/mod.rs (+2 lines)
- Export inline_boundary_builder module
- Public re-export of JoinInlineBoundaryBuilder
- MODIFIED: src/mir/builder/control_flow/joinir/patterns/pattern2_with_break.rs
- Replace direct boundary field manipulation with builder pattern
- 9 lines of field assignments → fluent builder chain
# Benefits
- **Centralized**: All boundary construction logic in builder
- **Readable**: Fluent API shows construction intent clearly
- **Maintainable**: Changes to boundary structure isolated to builder
- **Type Safe**: Builder validates field consistency
# Tests
✅ All builder unit tests pass (4/4)
✅ All pattern module tests pass (30+)
✅ Library build succeeds with no errors
🤖 Generated with Claude Code (https://claude.com/claude-code)
Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>
3645a3c2d2