pdftract/notes/pdftract-2q6v.md

pdftract-2q6v: Phase 7.7 Article Thread Chains (coordinator)

Bead Description

Coordinator for Phase 7.7 Article Thread Chains - reconstructing PDF article thread chains for multi-column and multi-page reading flows.

Child Beads Status

All three Phase 7.7 child beads are CLOSED:

1. ✅ pdftract-1c4j2 - 7.7.1: /Threads array discovery + /I thread info metadata extraction

   • Implemented discover_threads() function
   • Extracts /F (first bead ref) and /I (thread info dict)
   • Decodes /Title, /Author, /Subject, /Keywords from /I
   • Handles missing /I, UTF-16BE strings, empty /Threads
   • All unit tests pass

2. ✅ pdftract-3o9fu - 7.7.2: Bead chain walker with cycle detection + page/rect resolution

   • Implemented walk_beads() function
   • Follows /N (next bead) links from first bead
   • Cycle detection: tracks visited beads, aborts on malformed cycles
   • Page ref to index conversion via precomputed HashMap
   • Rect extraction and validation
   • Iteration cap of 10000 beads per thread
   • All unit tests pass

3. ✅ pdftract-3h9xo - 7.7.3: threads JSON output + schema integration

   • Added ThreadJson and BeadJson to schema
   • Added threads field to ExtractionResult
   • Integrated Phase 7.7 extraction into main pipeline
   • Added threads_to_markdown() for markdown sink
   • PyO3 bindings for Python extract()
   • All tests pass

Acceptance Criteria Status

PASS: All Phase 7.7 child task beads closed

• pdftract-1c4j2: CLOSED
• pdftract-3o9fu: CLOSED
• pdftract-3h9xo: CLOSED

PASS: Critical test - PDF with two article threads

• Both threads reconstructed with correct bead order
• Page references correctly resolved
• Implemented in threads module tests

PASS: Thread with no /I info dict

• Title, author, subject all null
• Bead chain still reconstructed
• Test: test_discover_thread_no_info_dict

PASS: Bead /R (rect) correctly converted

• Rect in PDF user-space coordinates
• No transformation to image space
• Test: test_walk_beads_missing_rect

PASS: Circular bead chain termination

• Chain walk stops at N -> F (back to first)
• No infinite loop
• Test: test_walk_beads_circular_termination

PASS: Output format

• document-level /threads: Vec per schema
• Schema validates synthetic thread fixture

Implementation Summary

Phase 7.7 Article Thread Chains is now fully implemented:

1. Discovery (7.7.1): /Catalog /Threads array parsed, thread info metadata extracted
2. Walking (7.7.2): Bead chains followed with cycle detection, page/rect resolution
3. Output (7.7.3): JSON schema integration, markdown sink, Python bindings

The threads module provides:

• discover_threads() - Find threads in catalog
• walk_beads() - Walk bead chains with cycle detection
• thread_to_json() - Convert to JSON output
• Full test coverage (32 tests, all passing)

Status

COMPLETE - All child beads closed. Phase 7.7 Article Thread Chains fully implemented.