Phase 4.6 Output Serialization (Plain Text Mode) coordinator is complete.
All 5 children beads are closed and all acceptance criteria PASS.
Acceptance criteria verified:
- All children closed: pdftract-56txm, pdftract-2bpzs, pdftract-38p8h, pdftract-3bgxq, pdftract-529te
- 10-page doc: 9 form-feed characters (test_serialize_document_text_ten_pages)
- Header excluded by default; included with flag
- Invisible Tr=3 excluded by default
- Text round-trips with join
Test results:
- text.rs: 160 tests passed
- options.rs: 41 tests passed
Closes pdftract-4453y.
