feat: expose reader activity and stable content coverage

[Eoic]

Summary

Expose optional, Goals-independent activity observations from the reader: content readiness, visibility, stable EPUB coverage, exposed PDF pages/spreads, navigation cause, and end-of-document state. Existing locator callbacks, version-1 locators, custom engines, and worker parsing remain compatible. Coverage reporting preserves exact EPUB content offsets during restoration/reflow.

Testing

• Package analysis and all 145 package tests pass, including panel visibility, custom engines, navigation, restoration, and large text.
• Example analysis/tests/web build and worker drift check pass.
• Browser smoke checks passed with worker, local-file, pagination, focus, settings, and theme coverage.
• Real EPUB/PDF Android and Chromium host integration passed in client #40.

Compatibility and migration

Additive callback and snapshot fields; no Goals dependency or package version change. Target development. Merge before the client pins this revision.

Notes

The host owns clocks, lifecycle, persistence, calibration, aggregation, and explicit completion. EPUB coverage is chapter-local normalized content, not screen pagination.

Coordinated server #12 and workspace integration pin these changes without a version bump.

Workspace integration #13 pins all three component revisions and documents release order.

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[chatgpt-codex-connector]

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-06T13:37:33.654960Z	bc617de	PR opened

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Reviewed commit: bc617deeaf

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