sicher/reveal: A screenwriting editor application. - Codeberg.org

The measure and draw passes re-flowed the entire document into pages every
frame. The flow is deterministic given (edit_version, page size, title-page
presence) and expressed in page-size-relative LINE units, so scroll and zoom
don't change it — memoize it.
`paginate(g)` fills g_pg (per-block page + start line + span + dual-pair end),
keyed on that signature; reset on doc swap. `renderDocument` reads positions
from the cache:
- measure: O(1) — caret via computeCaret (the cursor block may be off-screen),
 the whole-doc walk runs only when there's a click to resolve;
- draw: O(visible) — firstVisibleUnit binary-searches the first on-screen block,
 then the loop stops once past the viewport.
Verified identical output: Big Fish still 129 pages, deep scroll (caret at block
2400 → page 113/129) renders correctly with the right page numbers and caret.
Measured (Debug, simulated scroll, timeline open):
- Big Fish (2.7k blocks): 3.6ms → 2.2ms/frame.
- Monster (43.5k blocks): 39ms → 14.5ms/frame (1031ms → 14.5ms overall).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>