Stage-B minimal JoinIR lowering統一化:
1. Add Case-A helpers to loop_to_join.rs:
- lower_case_a_for_stageb_body (StageBBodyExtractorBox.build_body_src/2)
- lower_case_a_for_stageb_funcscanner (StageBFuncScannerBox.scan_all_boxes/1)
2. Update stageb_body.rs and stageb_funcscanner.rs:
- Replace manual LoopForm construction with construct_simple_while_loopform
- Route through LoopToJoinLowerer like other Case-A functions
- Remove unused imports (LoopForm, MirQuery)
Now all 6 JoinIR lowering modules use the same unified pattern:
- skip_ws, trim, append_defs, stage1_resolver, stageb_body, stageb_funcscanner
All route through LoopToJoinLowerer for consistency.
Test results: JSON snapshot 6/6 PASS
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Co-Authored-By: Claude <noreply@anthropic.com>
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