The vertical analog of per-system justification, and the first piece of the
deferred vertical spring solve: the systems of every non-final page spread so
the last system's bottom reaches the content bottom, filling the page height.
A second pass after the top-down stacking loop, once page membership is known:
for each non-final page with >=2 systems it computes the vertical slack (the
last system's natural bottom above the content bottom) and distributes it evenly
across the inter-system gaps — system i (0-based on the page) sinks by i/(n-1) of
the slack, so the first stays at the content top and the last lands on the
content bottom. Only Placement::dy changes, so it composes cleanly with
horizontal justification (independent axes). ENGRAVER_VERSION 8 -> 9.
The last page stays ragged-bottom (top-aligned, engraving convention), so a
single-page score is unchanged — every existing single-page golden is
byte-identical (zero golden churn). A single-system or already-full page has no
slack. Drives page_fill_efficiency to ~0 on justified pages.
Regression: vertical_justification_fills_non_final_pages (a small custom
PageGeometry forces the multi-page path; the non-final page fills, the last
stays ragged; verified to fail without the pass). Inter-staff band-height
renegotiation within a multi-staff system remains the deferred rest of the
vertical spring solve. 942 tests, clippy 0, docs -D warnings, conformance 8/8.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Levi Neuwirth
69e0430062