Add Phase 4 caption classification for detecting figure captions.
Implements classify_caption() which identifies blocks as captions when:
- Small font size (median < page body median)
- Follows Figure block within 2 line heights
- Same column as Figure
Module: crates/pdftract-core/src/layout/caption.rs
Acceptance criteria:
- Block immediately below Figure, small font, same column → kind: Caption
- Block 5 lines below Figure → NOT Caption (gap too large)
- Block with body-size font below Figure → NOT Caption (font not smaller)
- Block in different column from Figure → NOT Caption
Tests: 9/9 passed covering all acceptance criteria plus edge cases.
Closes: pdftract-xzfkt
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
Add MSRV (Minimum Supported Rust Version) pinning to 1.78 for
pdftract-core and pdftract-cli. The MSRV gate prevents silent
absorption of newer Rust features that would break downstream
consumers on older toolchains.
Changes:
- CI: Add quality-matrix DAG with msrv-check step (rust:1.78-slim)
- CI: Add clippy-check, fmt-check, cargo-audit, cargo-deny templates
- README: Add MSRV badge (shields.io)
- clippy.toml: Enable msrv=1.78 for MSRV-aware lints
- CONTRIBUTING.md: Document MSRV bump policy (MINOR version event)
The rust-version was already declared in workspace Cargo.toml;
this bead adds the CI enforcement and documentation.
Refs: pdftract-2w02
