jedarden c2fed3d010 docs(pdftract-63ka2): Add coordinator verification note for Phase 4.3 Column Detection

All 4 children verified closed:
- pdftract-56vwd: x0 histogram builder (7 tests PASS)
- pdftract-14w0w: Gap detection (13 tests PASS)
- pdftract-2rkc1: Column confirmation (14 tests PASS)
- pdftract-64j83: Column label assignment (5 tests PASS)

Total: 49 column tests PASS. Acceptance criteria verified for:
- Three-column layout detection
- Full-width heading handling
- Single-column page (no false splits)

Closes pdftract-63ka2

2026-06-07 08:38:28 -04:00

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pdftract-63ka2: Phase 4.3 Column Detection (coordinator)

Summary

Coordinator for Phase 4.3 Column Detection. All 4 child beads are closed with implementation and tests verified.

Children Status

Child ID	Title	Status	Verified
pdftract-56vwd	x0 histogram builder (1pt resolution)	closed	✓ May 25
pdftract-14w0w	Gap detection (>= 0.03 * page_width)	closed	✓ May 27
pdftract-2rkc1	Column confirmation (>= 3 lines)	closed	✓ May 27
pdftract-64j83	Column label assignment to spans/lines	closed	✓ May 24

Acceptance Criteria Verification

Criterion 1: All 4 children closed

Status: PASS

All 4 children have been closed with verification notes documenting their implementation and test coverage.

Criterion 2: Three-column academic paper detected

Status: PASS (verified via test_confirm_columns_three_column_all_confirmed)

Test creates 3-column layout with gaps at 200-219 and 400-419, 10 lines per column. Confirmed output: 3 columns with indices 0, 1, 2 and x_ranges [0,200), [220,400), [420,600).

Criterion 3: Full-width heading above two-column body

Status: PASS (verified via test_assign_columns_to_lines_full_width_heading)

Test verifies that when all spans on a line have column = None (full-width heading), the line's column is also None. Body spans in columns 0 and 1 are correctly assigned.

Criterion 4: Single-column page: no false splits

Status: PASS (verified via test_assign_columns_to_spans_single_column)

Test confirms single-column page (full-width x_range [0,600)) assigns all spans to Some(0). Also verified by test_confirm_columns_single_column_confirmed.

Test Coverage Summary

Total column tests: 49 tests, all PASS

build_x0_histogram: 7 tests
detect_column_gaps: 13 tests
confirm_columns: 14 tests
assign_columns_to_spans: 5 tests
assign_columns_to_lines: 5 tests
Supporting tests: 5 tests

Implementation Location

All code in crates/pdftract-core/src/layout/columns.rs:

build_x0_histogram() - lines 48-82
detect_column_gaps() - lines 156-201
confirm_columns() - lines 252-332
assign_columns_to_spans() - lines 428-437
assign_columns_to_lines() - lines 464-491
Supporting types: ColumnGap, Column, CandidateColumn
Traits: HasBBox, HasFirstSpan, HasBBoxAndColumn, HasSpansWithColumn

Critical Invariants Verified

3-line minimum: Enforced in confirm_columns filter (line 326)
Column gap threshold scales with page_width: (page_width * 0.03).ceil() (line 157)
Full-width lines get column = None: >50% dominance check in assign_columns_to_lines
Column indices monotonic left-to-right: Verified in tests

Gates to Next Phase

This coordinator completion gates:

Phase 4.4: Per-column block formation
Phase 4.5: XY-cut reading order

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