Story-2343: the Text lens reads in a reading column

UAT #2338 caught the Text lens rendering extracted text edge-to-edge across the window — 300+ characters on a line. Nobody reads that; the eye loses its place on the return sweep. Typography has one law here, the same law the Original lens's fit-width cap already obeys: a line of prose runs 60–75 characters. The Insights lens was already right (a centered ~720px column). The Text lens was not. This Story makes them the same column — literally the same number.

The idea in one line

One measure, one token. The 720px cap becomes --reading-measure, exposed to Tailwind as the reading container size, and both prose surfaces compose max-w-reading. There is no second magic number to drift from the first.

The token — and why it is NOT the existing one

Two caps, deliberately. A page of paper is a picture of a line, not the line itself — the ink inside an A4 render is already broken to its own measure, so the sheet may be wider. Live text is not: its cap is the measure. Collapsing them into one number would either shrink the paper or unbind the prose.

/* design/v1/colors_and_type.css — canonical */
--reading-measure: 720px;

/* globals.css @theme inline — the utility */
--container-reading: var(--reading-measure);   /* → max-w-reading */

The diff

• document-machine-copy.tsx — the article becomes mx-auto w-full max-w-reading: a centered column inside whatever space the lens gives it.
• document-insights-dossier.tsx — w-[720px] → w-full max-w-reading. Same rendered width, now derived from the token instead of restating it. This is the "one measure, not two magic numbers" acceptance criterion made literal.
• Rhythm inside the measure — the width alone does not make prose readable. Body text goes 13px/relaxed → text-[14px] leading-[1.75], paragraphs and lists get vertical air, block gap 3 → 4, and a heading block sits a rung above the body it opens (text-[15px] font-semibold text-ink-strong, with space above).

Sections rail and focus mode

Nothing to special-case, by construction. The column centers in the flex child it lives in, so it re-centers in whatever width remains when the sections outline is open, and again when focus mode hands the whole frame to the viewer. Section boundaries stay inside the column, still carrying data-section-id / data-page / data-block — so the outline's jump targets and the note anchors (SS-06) are untouched.

Evidence

Honest seams (verification doctrine)

Observability

Instrumentation-exempt per pramaan-docs ADR-124: presentational layout/CSS only — no new handler, route, job, or product-state transition.