Preserve word spacing across rotated text runs

[silverstein]

Summary

Preserve source-backed spaces between text runs on rotated pages. The layout builder previously measured gaps only in viewport x coordinates, which can turn a real gap into an apparent overlap on an upside-down page.

The shared implementation now projects adjoining edges along their co-directed text advance. Existing spacing thresholds, line grouping, source order, and degenerate/differently directed fallback remain unchanged. This also corrects spacing within already-grouped short quarter-turn runs; it does not reconstruct rotated paragraphs.

Source and packaged-share implementations are identical. The extraction oracle was regenerated through the existing generator; only three source-identity metadata values changed, not expected document results. No schema, tool registration, version or dependency change.

Verification

• Stonebook macOS 15.7.9, Intel x64, Node 26.5.0, one test worker.
• Initial focused/adjoining bank: 215/215 across eight files, including all three extraction-oracle suites.
• Reviewer-requested short-run expansion: 48/48 native PDF spacing cases. Runtime and oracle unchanged from the initial bank.
• Negative mutation restoring only the old gap formula: eight expected positive-gap failures, 40 passing controls.
• All rotations, offset CropBox/UserUnit, positive/touching/overlapping gaps, source/share parity, source replay, and mocked inverted LTR/RTL controls.
• Actual MCP development regression on independently transformed external PDF: 40/40 sampled text anchors and 5/5 geometry checks; original 39/40 failure preserved. Four unaffected variant bodies remain byte-identical. All conversions still report their unrelated partial-coverage gaps.
• Independent review approved exact 55a80765a0914cec462e12c01a762fb67d3c7c5b and separately verified the retained regression hashes and original failure. Full supported-runtime CI remains the merge gate.

No OCR, model/provider calls, release, whole-document completeness, or comparative benchmark claim.