Optimize sidebar unseen completion subscriptions

[cursor]

What Changed

• Replaced SidebarProjectItem's per-thread lastVisitedAt array subscription with a derived hasUnseenCompletion selector.
• Added shared hasUnseenCompletionSinceVisit logic so project status derivation and thread status logic use the same completion/visit semantics.
• Added focused coverage for repeated post-completion visit updates and invalid visit timestamps.
• Included react-scan before/after recordings:
  • artifacts/react-scan/sidebar-before.webm
  • artifacts/react-scan/sidebar-after.webm

Why

React Doctor/manual review showed the sidebar project row subscribed to every visit timestamp for every thread in a project. Updating a hidden thread's visit timestamp could rerender the project group even when the visible project status did not change. The new selector only changes when the derived unseen-completion boolean changes, preserving status behavior while avoiding rerenders for timestamp churn that is not user-visible.

React Scan scenario used for both videos: seed one sidebar project with 24 completed threads, then repeatedly mark a hidden already-seen thread as visited with later timestamps. Before the fix, the sidebar project group highlights repeatedly; after the fix, the status selector remains stable for those updates.

React Doctor was run pre/post scan. The post-fix diff report still lists broader pre-existing Sidebar/ChatView/CommandPalette findings on the branch, but this PR intentionally addresses only the sidebar visit-status rerender hotspot.

UI Changes

Before/after react-scan recordings are committed in this PR:

• Before: artifacts/react-scan/sidebar-before.webm
• After: artifacts/react-scan/sidebar-after.webm

Checklist

• This PR is small and focused
• I explained what changed and why
• I included before/after screenshots for any UI changes
• I included a video for animation/interaction changes

Verification:

• bun fmt
• bun lint
• bun typecheck
• bun run --filter @t3tools/web test src/components/Sidebar.logic.test.ts
• bunx react-doctor ./apps/web --full --json --no-score --no-telemetry
• bunx react-doctor ./apps/web --diff main --json --no-score --no-telemetry

  

Note

Optimize sidebar unseen completion subscriptions in SidebarProjectItem

• Extracts a new hasUnseenCompletionSinceVisit function in Sidebar.logic.ts that compares raw completedAt and lastVisitedAt timestamps, and refactors hasUnseenCompletion to delegate to it.
• In Sidebar.tsx, replaces per-thread lastVisitedAt state subscriptions with a pre-computed boolean array projectThreadHasUnseenCompletions, reducing the number of reactive state reads.
• Behavioral Change: resolveThreadStatusPill now receives lastVisitedAt: undefined when a thread has an unseen completion, and lastVisitedAt equal to latestTurn.completedAt otherwise — previously it always received the persisted lastVisitedAt from state.

^{Macroscope summarized 237ffdb.}