fix(ui): stop overriding Astryx's chat bubble radius

[Astro-Han]

Summary

The bubble and the composer are designed to share one radius token. ChatMessageBubble defaults to var(--radius-chat) (28px); ChatComposer reads the same token via --_chat-composer-radius. The product overrode the bubble twice — density="compact" dropped it to 12px, then .maka-chat-message-bubble-user pushed it to 10px — and left the composer alone.

Full view, light (top) then dark (bottom). Story product-shell-official-appshell--native-conversation, 1180×788 @2x, scrolled to top.

Corner zoom on the bubble/dock join, light (top) then dark (bottom). Same story and conditions. The AFTER bubble sits ~32px lower: the balanced tier lengthens the transcript.

Three deletions, no new value. 28px is what the component picks on its own once both overrides are gone.

density is a spacing tier, so dropping it also moves ChatMessage's children gap 2px → 4px and the transcript reads looser — bundled with the tier, intended. Bubble padding is not affected: Astryx's paddingCompact and paddingBalanced resolve to the same StyleX atoms.

DESIGN.md §6 moves in the same commit because it contradicted the change: chat bubbles leave the 10px card row, a 28px chat rung records what --radius-chat governs, and the Two-Name Rule no longer claims nothing in the product renders at 28px — ChatComposer already did, on main.

Refs #3446 — same root as its F1 finding, separate intent, none of its other work folded in.

Verification

Playwright computed-style sweep against a live Storybook dev server, before and after, same branch and same server. Page pinned, scrollTop 0, identical framing. Light and dark — identical results in both.

	before	after
user bubble	10px	28px
assistant bubble	12px	28px (ghost, transparent)
user bubble padding	12px 16px	12px 16px
composer drawer	28px 28px 0 0	28px 28px 0 0
list density	compact	balanced

Full-page sweep of every visible element's radius, font-size/line-height, colour and gap. Everything that moved is accounted for, nothing else:

• radius 10px ×35→32, 12px ×3→1, 28px ×1→6 — distinct radii stay at 10, no new value in the ladder
• gap 2px ×11→5, 4px ×22→27 — ChatMessage's childrenGap, the tier's own spacing
• 435→431 visible elements — signature diff shows every other element is the same element with compact renamed to balanced; the four that leave are the last message's tail, pushed below the fold as scrollHeight grows 1473→1505px
• no font-size/line-height pair or colour value added or removed

density="compact" on <Markdown> (chat-turn.tsx:1107) is left alone — a different density axis with its own [data-density="compact"] contract.

Ran: npm run format (no fixes), @maka/ui tsc build (clean), focused tests chat-turn-answer-identity / chat-turn-steering-order / chat-conversation-items / transcript-projection (23 pass, 0 fail). Not run: repo-wide suite (CI), desktop Storybook visual smoke.

Review focus

packages/ui/src/chat-surface-layout.tsx:35 says chat-surface-layout.test.tsx holds the balanced density value. That file does not exist in the repo — the ChatLayout density default is currently unguarded. Out of scope here, worth a follow-up.

DESIGN.md §6 is a deliberate revision of the design authority, written as a rule rather than an exception. Please review that wording as policy.

AI use

• No generative tool made a substantive contribution
• Generative tooling made a substantive contribution

Tool(s) and scope: Claude Code — the deletions, the DESIGN.md §6 revision, the CSS comment rewrite, the Playwright measurement harness, and this body. Every number above comes from that harness against a live server, not from reasoning about the cascade. Commit carries a Generated-by: Claude Code trailer.

Checklist

• Tests cover the change and fail without it
• Lint, format, typecheck and the affected suites pass locally

Does this PR entail a change in behavior?

• Yes — described under Summary above
• No

[jackwener]

Automated review of exact head 1a99e766ef824bc69d0f5a2548df6257c7cc1084 against current main@d62857a8357e9160926726a2a13096bc2dc2b91d.

The defect remains on main: both ChatMessageList call sites force compact, which activates Astryx's compact bubble radius, and product CSS then overrides the filled user bubble again to 10px while the composer independently stays on --radius-chat (28px). The patch removes both competing product decisions and lets the shared primitive/token own the shape; the measured padding result also confirms this is not compensating with a new value. I found no actionable P0-P2 defect. Required test is green and the PR includes before/after visual evidence.

Required conclusions:

1. Optimal for the actual problem: yes; deleting the two overrides restores the existing Astryx source of truth.
2. Production code to delete: the PR already deletes the unnecessary density="compact" props and product radius override; none further identified.
3. Tests to delete/replace: none identified.
4. Deeper refactor: no.
5. Ready to merge: code-wise yes, but this automated review is not approval; the visual/design-policy change still needs independent human review.
6. Residual risks/gaps: no automated computed-style regression protects the 28px pairing, so the supplied visual evidence and a human check are the current guard; future Astryx changes could move the default.

This affects user-visible layout and DESIGN.md policy, so CONTRIBUTING.md requires independent human judgment on the exact head.