[yhay81]

Closes #729

A page's /UserUnit scales its display coordinates to physical points (1/72 inch), following the owner's decision. A page with /MediaBox [0 0 400 300] /UserUnit 2 measures 800 by 600 points and renders at 800 by 600 pixels at 72 dpi.

What changed

• The page index resolves the page’s own finite, positive /UserUnit through the store. Missing or invalid values use 1. For a reference chain it records each object read, so editing the last object updates derived geometry. Invalid containers are never copied for the unit.
• For scaled pages, the bindings and the interpreter use the same full-precision box, rotation and unit. Raster dimensions, clipped and batch rendering, text layout and content extraction use that geometry. Narrow crops keep their true visible extent and origin. Unit-one rendering retains hayro's native viewport.
• The SVG root carries the physical dimensions and the corresponding viewport in hayro's drawing coordinates. The existing string is edited in place, after checking the final byte length and budgeting any capacity growth.
• Page boxes and setters, annotations and links, canvas drawing and page placement, OCR and rotation removal use physical points. The canvas writes the inverse matrix at round-trip precision and uses the same coefficients for its patterns.
• The English and Japanese concepts pages and the page API document physical points. Internally, _core.page_space returns (rotation, box, unit) and _core.canvas_source_page carries the unit after the box.

Acceptance

• The owner recorded the display-space decision on Honor or expose /UserUnit in page geometry and rendering #729.
• Public API tests cover units 1 and 2, raster dimensions and pixels at 72 and 144 dpi, extraction and search, clipping, page boxes and rotation, annotations and links, canvas, OCR, indirect values, edits and undo.
• Review regressions cover a saved canvas and gradient at units 750 and 30000, a two-hop unit reference, indirect box coordinates, all four rotations of a sub-unit crop, a 52010-pixel decimal page including its final column, and the exact SVG output limit. Rust tests cover invalid-unit retention, SVG buffer growth, and raw RGBA rendering.

Checks

python3 tools/check.py --locked passed on 89287512. The Python suite passed 8,205 tests and the Rust workspace passed 665 tests. Ruff, ty, rustfmt and Clippy also passed.

Follow-up

• Measure annotation and widget lengths in points on /UserUnit pages #736 tracks annotation and widget stroke widths, dash lengths and font sizes.
• The next release should list the coordinate and render-size change on pages with a non-default unit under “Changed”.

Not a port from pylopdf.

[yhay81]

I recommend fixing the four coordinate errors and the two unbudgeted copies below before merging. I reproduced the coordinate errors on 8e111a7b through the public Python API. All 433 tests in the ten related test modules passed locally, and the current head passed CI.