Layout: breakable paragraphs across columns, sidebar gets its own flexible track at every width, cols requires multiple paragraphs; h3 size fix in corporate theme

docs/design-principles.md

@@ -34,7 +34,7 @@ Pagerite is a single-user CMS/blog. This document records the initial high-level
 
 ## Reading experience
 
-- The article column is sized by the **viewport, never by content**: a symmetric grid (`1fr minmax(0, 78rem) 1fr`) with flexible gutters keeps the layout stable across navigation. The sidebar occupies the left gutter, the right gutter balances it. Long articles (flagged `.multicol` by the backend render) lift the cap and become a bounded **composition**, centered in the available space with the surplus left vacant: a fluid text lane (up to 42rem) plus a 16rem **side zone at the article's left** — the region the nav sidebar overlays — which hosts margin boxes (`.margin`, `::: aside`, margin figures) at all but phone widths, without the text ever moving. On pages with a sidebar below ~110rem (where the sidebar gets its own 12rem track) the track is the left lane instead: no in-article zone, the text lane runs fluid up to 86rem, and the boxes fall into the track, sliding under the translucent sticky nav. Once two lanes fit beside the zone (≥96rem available in `main`), the text flows in two fluid lanes (36rem minimum, capped at 102rem total — technical content wants the wider lanes, and wider windows just add vacant space). The stages step by the space actually available in `main` (container queries + `cqw` units, so the docked editor's inset is automatic). `.wide` figures on multicol pages bleed to the viewport edges measured from `main` (`cqw`), sliding under the sidebar. The backend splits the body into `.colseg` segments at h1/h2 headings, `.wide` elements and margin blocks (full-width separators or margin boxes, never inside columns), tagging segments that hold enough text with `.cols` — code blocks are excluded from that measure, and a `::: nocols` container opts its whole section out. On wide single-column pages (≥104rem), margin boxes lean into the vacant left gutter as well.
+- The article column is sized by the **viewport, never by content**: a symmetric grid (`1fr minmax(0, 78rem) 1fr`) with flexible gutters keeps the layout stable across navigation. The sidebar occupies the left gutter, the right gutter balances it. Long articles (flagged `.multicol` by the backend render) lift the cap and become a bounded **composition**, centered in the available space with the surplus left vacant: a fluid text lane (up to 42rem) plus a 16rem **side zone at the article's left** — the region the nav sidebar overlays — which hosts margin boxes (`.margin`, `::: aside`, margin figures) at all but phone widths, without the text ever moving. On pages with a sidebar, the sidebar gets its own track at every width — flexible, 12rem when space is tight and growing up to 150% (18rem) once the viewport has room beyond the article, the sidebar keeping its left side on the viewport's edge — and the track is the left lane instead: no in-article zone, the text lane runs fluid up to 86rem leaning on the viewport's right edge (surplus extends the left lane), and the boxes hang into the lane off the article's left border (growing leftward with it, up to 18rem), sliding under the translucent sticky nav. Once two lanes fit beside the zone (≥96rem available in `main`), the text flows in two fluid lanes (36rem minimum, capped at 102rem total — technical content wants the wider lanes, and wider windows just add vacant space). The stages step by the space actually available in `main` (container queries + `cqw` units, so the docked editor's inset is automatic). `.wide` figures on multicol pages bleed to the viewport edges measured from `main` (`cqw`), sliding under the sidebar. The backend splits the body into `.colseg` segments at h1/h2 headings, `.wide` elements and margin blocks (full-width separators or margin boxes, never inside columns), tagging segments that hold enough text in at least two paragraphs (or one long enough to split) with `.cols` — code blocks are excluded from that measure, a `::: nocols` container opts its whole section out, and column-filling paragraphs are marked `.breakable` so they may split across the column gap (shorter paragraphs stay whole). On wide single-column pages (≥104rem), margin boxes lean into the vacant left gutter as well, growing with it up to 18rem.
 - A gentle **scroll-reveal** of headings, figures and block-level elements (IntersectionObserver). It is layout-level: articles need no support for it, and `prefers-reduced-motion` disables all motion.
 
 ## Styling