docs(pdftract-1n8): add Phase 7.1 coordinator completion note

Phase 7.1 StructTree Exploitation coordinator bead complete. All 4 child
task beads closed:
- 7.1.1: StructTree depth-first walker + /RoleMap resolution
- 7.1.2: Element-type to block-kind mapping table
- 7.1.3: ParentTree-based MCID-to-StructElem resolver
- 7.1.4: Coverage check + XY-cut fallback for Suspects pages

Acceptance criteria:
- Word H1/H2 -> heading level 1/2: PASS
- /ActualText on ligatures: PASS
- /Artifact content suppression: PASS
- Suspects -> XY-cut fallback: PASS

Co-authored-By: Claude Opus 4.7 <noreply@anthropic.com>

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+# pdftract-1n8: Phase 7.1 StructTree Exploitation (Coordinator)
+
+## Status: COMPLETE
+
+## Summary
+
+Phase 7.1 coordinator bead. All 4 child task beads have been successfully completed:
+- 7.1.1 (pdftract-1x2): StructTree depth-first walker + /RoleMap resolution - CLOSED
+- 7.1.2 (pdftract-2ork): Element-type to block-kind mapping table - CLOSED
+- 7.1.3 (pdftract-57o4): ParentTree-based MCID-to-StructElem resolver - CLOSED
+- 7.1.4 (pdftract-2w3r): Coverage check + XY-cut fallback for Suspects pages - CLOSED
+
+## Acceptance Criteria Status
+
+### Critical Tests (from plan)
+
+| Criterion | Status | Notes |
+|-----------|--------|-------|
+| Word-generated tagged PDF: heading levels correctly extracted (H1/H2 map to level 1/2) | PASS | Implemented in 7.1.2 block-kind mapping |
+| Tagged PDF with /ActualText on a ligature: ActualText value used, not glyph-decoded text | PASS | /ActualText handling in 7.1.1 walker |
+| Tagged PDF with /Artifact marked content: artifact glyphs excluded from output | PASS | /Artifact suppression in 7.1.2 mapping |
+| PDF with Suspects true: falls back to XY-cut, reading_order_algorithm = "xy_cut" | PASS | Implemented in 7.1.4 coverage check |
+| CI test fixtures: tagged-word.pdf, tagged-latex.pdf, tagged-actualtext-ligature.pdf, tagged-artifact-header.pdf, tagged-suspects-true.pdf | PASS | All fixtures covered in child beads |
+
+### Coordinator Criterion
+- **All Phase 7.1 child task beads closed**: PASS (4/4 closed)
+
+## Child Bead Artifacts
+
+### 7.1.1 (pdftract-1x2)
+- StructTree depth-first walker implemented
+- /RoleMap resolution with chain detection
+- /Lang and /ActualText inheritance
+- Unit tests for Word RoleMap, nested /Lang, /ActualText scope
+
+### 7.1.2 (pdftract-2ork)
+- StandardType -> BlockKind mapping table
+- /Artifact suppression (both structure type and marked-content tag)
+- Heading-level extraction (H1..H6 -> heading{level})
+- Unknown-type fallback with diagnostics
+
+### 7.1.3 (pdftract-57o4)
+- ParentTree number-tree walker
+- Per-page MCID -> StructElem map
+- Orphan MCID detection
+- Annotation /StructParent linking
+
+### 7.1.4 (pdftract-2w3r)
+- Coverage calculation (claimed MCIDs / total MCIDs)
+- Per-page XY-cut fallback for Suspects + low coverage
+- reading_order_algorithm field ("struct_tree" vs "xy_cut")
+- Per-page diagnostic on fallback
+
+## Verification
+
+No code changes required for this coordinator bead - all implementation work was done in child beads. This note documents the successful coordination and completion of Phase 7.1.
+
+## References
+- Plan section: 7.1 StructTree Exploitation (lines 2543-2564)
+- Parent tree integration tests: pdftract/tests/pdf/parent_tree/
+- StructTree coverage check: commits 9bd4a23, 566cac2