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/backend.md

@@ -20,7 +20,7 @@ msgspec Structs for the kanta database. See `docs/content-model.md` for the full
 
 markdown-it-py renderer (html passthrough + attrs, footnote, deflist, tasklists, admon, gfm_autolink, sub/superscript plugins; typographer + breaks on). In bodies with at least three top-level h1/h2 headings (nested ones, e.g. inside `::: aside`, never participate), each gets a slug id (`python-slugify`, mirroring the editor's `slugify.js` — unicode folds to ASCII, separators become single hyphens) unless the author set `{#id}`, and their text is wrapped in a self-link (`a.anchor`) so section links are copyable; anchored headings also carry `data-line` with their markdown source line (the page editor's section pens and piecewise scroll sync key off it); the first in-body h1 is the article title — when the markdown has no h1, `render(title=...)` injects it as `# {title}` so implicit and explicit titles take the same path — it gets no id and doesn't count toward the three, its self-link is `href=""` (scroll to top); shorter articles stay anchor-free, h3+ is never navigable, and duplicates get `-2`/`-3` suffixes. Custom image rule: relative srcs resolve against the page path; an image standing alone in its paragraph becomes a figure (captioned when titled), while inline-with-text images and raw `<img>` HTML stay plain. A `{dates}` line expands to the article's published/updated dateline (`p.dateline`, from `Node.created`/`modified`; left literal in previews of unsaved pages).
 
-`render()` returns a `Rendered(html, multicol)`: the article content segmented for the column layout (there is no wrapper div — segments and bare blocks are direct `<article>` children) — h1/h2 headings, `.wide` blocks and margin-breakout blocks (`.margin`, `::: aside`) stand bare, the runs between them become `<div class="colseg">` (plus `.cols` on segments with enough text, `::: nocols` opting out), and `multicol` flags bodies long enough to columnize (visible-text thresholds, code excluded). `views.py` puts the class on the article; pagerite.css takes it from there (at most two columns, the left-margin breakout, all viewport adaptation).
+`render()` returns a `Rendered(html, multicol)`: the article content segmented for the column layout (there is no wrapper div — segments and bare blocks are direct `<article>` children) — h1/h2 headings, `.wide` blocks and margin-breakout blocks (`.margin`, `::: aside`) stand bare, the runs between them become `<div class="colseg">` (plus `.cols` on segments with enough text in at least two paragraphs or one long enough to split across columns, `::: nocols` opting out; in column segments, paragraphs past `BREAKABLE_TEXT` visible characters are marked `.breakable` so they may split across columns), and `multicol` flags bodies long enough to columnize (visible-text thresholds, code excluded). `views.py` puts the class on the article; pagerite.css takes it from there (at most two columns, the left-margin breakout, all viewport adaptation).
 
 ## `views.py`
 

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