refactor(compiler): reorganize StageBBodyExtractorBox structure
**Goal**: Improve readability of 480-line build_body_src method with
clear phase separators, consistent spacing, and unified formatting.
**Zero logic changes** - behavior 100% identical.
**Structure improvements**:
1. **Added clear phase separators** with ==== comment lines:
- Phase 4: Body extraction (k0/k1/k2/k3 logic)
- Phase 4.7: Comment removal
- Phase 4.5: Bundle resolution
- Phase 4.6: Duplicate bundle check
- Bundle merge + line-map debug output
- Using resolver
- Phase 5: Trim (left/right)
2. **Improved readability**:
- Added consistent spacing between phases (2 blank lines)
- Unified indentation (2 spaces throughout)
- Grouped related debug blocks together
- Made block structure more visible
3. **Zero logic changes**:
- All variable names unchanged
- All conditions unchanged
- All calculations unchanged
- All DEBUG messages unchanged
- All bundle/using resolver calls unchanged
**Verification**:
- Same ValueId(17) error as before (expected, will fix in Task B)
- Debug logs identical ([plugin/missing], [DEBUG])
- Behavior 100% identical to original
**Impact**: Code now much more maintainable with clear phase boundaries,
making future modifications safer and simpler.
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>
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