Sidebar can miss unread Completed status for newly finished threads

With a newly completed background thread, when completed, the sidebar entry switched to the already-viewed/idle state instead of showing the unread Completed dot/status.

My agent claims to have tracked it down to visit-state seeding:

New thread UI state can be seeded from the thread activity timestamp:

seedVisitedAt: thread.updatedAt ?? thread.createdAt

For a just-completed thread, updatedAt can be equal to or later than latestTurn.completedAt. The sidebar's unread-completion check uses a strict comparison:

latestTurn.completedAt > lastVisitedAt

That means if lastVisitedAt is seeded to completedAt or later, the completed thread is treated as already viewed even when the user has not opened it.

Minimal bad state:

latestTurn: {
  state: "completed",
  completedAt: "2026-04-13T00:05:00.000Z",
},
updatedAt: "2026-04-13T00:05:00.000Z",
threadLastVisitedAtById: {
  [threadKey]: "2026-04-13T00:05:00.000Z",
}

Agent's suggested fix: for first-observed completed threads after initial bootstrap, seed visit state before latestTurn.completedAt so they appear unread. Initial bootstrap history should still seed as read, so old completed threads do not all show as newly completed.

And suggested regression coverage:

• first-seen completed thread-upserted shows unread Completed
• same case with updatedAt > completedAt
• post-bootstrap snapshot introducing a completed thread shows unread Completed
• initial bootstrap historical completed threads stay read
• non-completed settled turns do not show Completed

Hope that's helpful! Thanks for the great work on t3 code ❤️

Start at the visit-state seeding path for new thread UI state and the sidebar unread-completion check using latestTurn.completedAt and lastVisitedAt. Add regression coverage for first-seen completed thread-upserted events, updatedAt later than completedAt, post-bootstrap snapshots, historical bootstrap threads, and non-completed settled turns. Done means new completed threads show unread Completed while initial history remains read.