[Astro-Han]

Summary

• Extract the complete materialized-turn renderer from chat-view.tsx into one cohesive chat-turn.tsx module.
• Keep ChatView responsible for transcript materialization, streaming-tail selection, scroll lifecycle, and page composition.
• Move turn-specific source contracts to the new owner without changing rendered DOM or behavior.

Why

Stage 2 of #829. ChatView still implemented attachments, message bodies, timeline entries, streaming/thinking content, lineage, and footer actions inline. Those concerns change as one rendered-turn subsystem, independently of the page container and its scroll lifecycle.

Refs #829.

Scope

This is a pure extraction. It does not redesign turn rendering, split every child component into a separate file, or move the #828 pinned-bottom and turn-size-warmup lifecycle out of ChatView; that scroll boundary is Stage 3.

Verification

• npm --workspace @maka/ui test — 111 passed.
• npm --workspace @maka/desktop test — 2,351 passed.
• npm --workspace @maka/desktop run typecheck:stories — passed.
• npm --workspace @maka/desktop run e2e -- scroll-geometry.spec.ts — 3 passed, including the section-switch re-warm contract from fix(ui): stabilize long-session scroll geometry for content-visibility turns #828.
• Production build completed during E2E setup.
• Codex review round 1 found one P1: a Storybook type still deep-imported TurnFooterActionMeta from chat-view.js. The import now uses the existing public components barrel and Storybook typecheck passes.
• After fix(ui): stabilize long-session scroll geometry for content-visibility turns #828 merged, the branch was rebased onto current main; the warm-up conflict was resolved by keeping scroll lifecycle in ChatView.
• Codex review round 2 after rebase and full verification: PASS, no P0–P2 findings.
• No visual evidence: declarations and DOM were moved unchanged. Full rendering contracts and the deterministic scroll-geometry E2E suite are the substitute evidence.

Impact

No user-visible, storage, migration, documentation, or release-note impact. Public @maka/ui type exports remain unchanged.

Reviewer notes

Review chat-turn.tsx as a moved cohesive unit. TurnView and the two fallback indicators are exported only for the internal ChatView seam; the package barrel continues to expose only the existing turn metadata types.

Ready for review

• Verification is complete and the results above are current
• Impact, compatibility, migration, documentation, and release-note needs are addressed
• User-visible UI/UX changes include visual evidence, or Verification explains why it is not applicable