[Eoic]

Closes #13. Supports FR-3_1 and FR-3_2.

EPUB opening now uses the host loading builder through initial pagination, keeping its position, theme and background without the separate “Preparing pages…” indicator. Reading settings provide a compact Slide / None dropdown. Instant turns respect system reduced motion and preserve selection and saved positions.

Page turns now use a larger buffer and avoid waiting for unrelated preparation:

• Prepare the visible spread first, then maintain five spreads ahead and retain measured pages for reversing direction.
• Prepare neighboring spine items independently, including the previous item's tail within three spreads of its boundary. A blocked next item cannot prevent backward preparation.
• Warm nearby illustrations five spreads ahead and three behind using Flutter's image cache.
• Start exact counting after the current buffer is ready. Prepared turns do not wait for another page beyond the destination.
• Update the viewport's extent before an immediate turn to a newly prepared page, so its displayed and persisted locations stay aligned.

Slider navigation uses the latest destination. New drags and releases invalidate queued intermediate seeks and cancel active EPUB seek waits. Layout checks cancellation at yields, reusable pages stay cached, and late results or errors cannot replace the latest location. Background snapshots cannot move the slider thumb while dragging. Ordinary page turns stay ordered. Already-running worker parsing may finish into the cache, and engines without cooperative cancellation finish their active operation before the latest queued seek.

Custom panels can reuse the reader header through ReaderPanelContext.buildHeader, so the client's Contents and Reading settings share title typography, spacing, close button and divider.

After initial preparation, safe-area insets retain the page background through chapter transitions and typography reflows. A new document load restores the host-colored opening background. A real EPUB regression with nonzero insets covers these transitions and failed before the correction.

Validation:

• All 231 reader tests passed. Regressions cover five ready forward turns, reversing direction, blocked neighbors in either direction, and immediate navigation after opening. Buffering and early-position regressions failed before their respective fixes. New tests cover coalesced slider releases, stable drag previews, stale errors, cancelled EPUB reads/layout, and a real viewport showing and persisting only the latest destination.
• Reader/example analysis, example tests and web build passed.
• Browser smoke passed for rapid back-and-forth slider drags, EPUB/PDF navigation, responsive settings, motion controls and opposing app/reader themes. Desktop and phone dropdowns were visually inspected.
• Integration and the exact Git pin are in fix: integrate reader preloading and saved animation controls client#103.

No migration or version bump. Cold seeks and uncached previous-section tails can still require yielding layout. Synthetic checks do not certify performance on every device or publisher file.

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-29T19:15:20.368104Z	95ea8ea	PR opened

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