feat(ui): rem-based type scale, mobile chat sizing, accent contrast fixes - #21

Started as "is the chat font on mobile big enough?". The answer was that it clears WCAG's formal bar and not much else — WCAG sets no minimum font size, and the viewport allows pinch-zoom, so nothing fails on size alone. But the audit turned up five real contrast failures next door, so this PR covers both.

Before / after

390px viewport, rendered against the compiled CSS of main and of this branch, so the two halves differ only by this change.

Light

Dark — note the attachment panel, which used to darken the accent in both themes and now lightens here:

The type scale is now rem

Every size in the app was a hardcoded text-[Npx] — 141 of them across 12 components, in 23 distinct sizes. A px size is frozen at whatever was typed, so a reader who raised their browser's default font size gets nothing back. Pinch-zoom satisfies WCAG 1.4.4 on its own; it does not stand in for honouring the setting.

Replaced with eleven named steps defined in styles.css, all rem:

Sizes are named by role, not by measurement, so the scale can be retuned in one place. marketing.css loses its font-size: 16px root pin for the same reason — the rest of that sheet was already rem, so the pin was silently discarding the preference for the whole page.

The floor is 11px: Apple's HIG says never below 11pt and Material's labelSmall is 11sp, and the app shipped 9.5px and 10px labels under both.

The chat steps up on mobile

No breakpoint in Chat.tsx touched font size — max-md: only adjusted padding and widths, so a phone got the desktop density unchanged. Bubbles now go 14.5 → 16px on narrow screens, metadata 11 → 12.5px, file names 13.5 → 14.5px. For reference, WhatsApp, Telegram and iMessage all sit at 16–17px in the bubble.

Contrast fixes (WCAG 1.4.3 — small text needs 4.5:1)

Secondary copy on a sent bubble was on-accent at 70–75% alpha, and the "couldn't decrypt" line used opacity-75 for the same effect. The accent only clears full-strength text by ~5.4:1 to begin with, so any alpha under ~90% lands under the minimum:

All four now use a solid --c-on-accent-muted token rather than an alpha, which is the same design intent at a legible contrast.

The fifth was structural: the attachment panel inside a sent bubble darkened the accent in both themes. The dark theme puts near-black text on a light accent, so darkening pushed the file name itself to 4.17:1 and its action icons to 2.58:1 (1.4.11 asks 3:1 for non-text). The panel now lightens in dark, restoring 6.9:1.

Two more papercuts

• iOS auto-zoom. Safari zooms the viewport when a field under 16px takes focus, and never zooms back out — so opening the composer left the chat mis-scaled. Every text entry point (.field-input, the composer, the linking-code textarea) now steps up to 16px on mobile.
• Retry target. The inline "Retry" on a failed message was a bare run of 10px text, ~13px tall. Now 24×24 minimum per WCAG 2.2 SC 2.5.8.

Verification

• Contrast ratios computed from the actual token values, including the alpha compositing over the accent and over the attachment panel — every number in the tables above is measured, not estimated.
• The captures above: both builds rendered side by side at 390px in both themes, with the real webfonts, to confirm the tokens resolve and the hierarchy still reads.
• pnpm build, pnpm lint, pnpm format:check clean; 382 tests pass.

AGENTS.md gains a short Typography section so the scale doesn't rot back into arbitrary px.