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Pair with Core #986

Unfinished source checkpoint 8998b6f8b. Do not build/install yet. The manifest/lock still pin the earlier Core 04d414e4b, not the current Core #986 f1e3866e0; that pin will be updated once the complete owner integration is ready. The historical header consumes E2E #965's birth_description API at 2979497b, pending Claude review before integration. Core #987's final canonical model/context owner and Toad #693's status/activity changes also land first; only unread hunks here change conversation_kind.py.

Core's existing observation family owns sidebar answers. Native tabs use canonical keyed rows, history tabs call channel_unread(target)/bus_unread(target), and relationship rows ask that observation to build the row. Foreign roots use WaitingSidebar and remain unobserved. Welcome/sidebar rendering consumes the keyed-model lifetime, not a duplicate snapshot-readiness flag. All raw-snapshot unread callbacks and their function-local imports are gone.

The read-position notifier consumes the Core notice member's messages_since(previous), rather than probing nullable text. Historical message headers consume the original ThreadIncarnation member's birth_description, never a nullable copied float or an unrecorded marker printed as a real birth. No new widget state copy, cache, codec or fallback.

Five earlier snapshot-consumer sites across four files were removed. The current Core counts are historical_views.py 8→0, sidebar.py 6→1; the remaining row model annotation awaits #987's canonical required thread.model. Original source data and uncertain inputs remain untouched.

Verification

Earlier paired source: actual live Core roster/derivation passed; 40 focused checks passed with one unchanged-main stale ThreadStatusModel.available assertion, owned by core-goal-retry. The earlier Core/Toad debt checks had zero increases; these are not final-head claims.

Current Core source: the real attached immutable archive reader returned a bounded original row with typed sender/target births and codec roundtrips, with original source fences intact and no input/attach. The final notice contract has 3 checks passed in 0.49s. Two larger serial Core batches and the combined ratchet reached their time bounds and have no final pass result; logs remain preserved.

The final source/debt checks and actual saved-session st/isolated-display sidebar/tab/filter journey remain pending complete owner integration and Codex's matching reviewed build. Verification stays with this implementation owner. No Toad tests, fixtures, fake responses or synthetic application; no installed-runtime/UI-success claim. No new native/provider input, build, installation, restart or data carry. Ordered deadline: 16:00 EDT.

[trissim]

Closing: its Core pair #986 was closed unmerged; the body marks it an unfinished checkpoint.