Patch sidebar rows from change metadata; weak ETag; search keepPreviousData (B1, B27, E8)

[SawyerHood]

What was wrong

• Every thread status, title, pin, environment or background-activity change made the browser refetch the unbounded GET /sidebar-bootstrap (all non-archived threads across all projects). status-changed flushes immediately and fires at least twice per turn, so a phone re-downloaded the whole sidebar several times per turn (B1).
• The sidebar search panel replaced its rows with a spinner while debouncing/fetching and remounted every row per keystroke (B27).
• Tapping a search result ran navigate, the drawer close and setIsActive(false) in one event handler, so React committed the thread mount, the drawer closing flip and the full thread-list remount in one task before the first slide-out frame could paint (E8).

What changed

• Server: NotificationHub.setThreadChangeMetadataEnricher (installed by createApp) attaches the thread's current ThreadListEntry as metadata.listEntry to row-only changes when a client is subscribed to the list or the thread. Membership changes carry no row. Enrichment never throws; failures fall back to the original metadata.
• Server: /sidebar-bootstrap serialises once, sends ETag: W/"..." + Cache-Control: private, no-cache, and returns a bodyless 304 for a matching If-None-Match (services/lib/weak-etag.ts).
• Domain: threadChangeMetadataSchema.listEntry (strict) and a lenient inbound twin that drops an unparseable row (.catch(undefined)).
• Client: patchThreadListRowsFromListEntry replaces the row in every cached thread list and the sidebar navigation (updateCachedThreadListEntry); it falls back to the previous invalidation when the row is absent, the thread is not in the cached sidebar, a bootstrap fetch is in flight, or the row left the sidebar membership. status-changed, title-changed, pin-state-changed, environment-changed and background-activity events-appended use it.
• Client: useThreadSearch keeps previous data (keepPreviousData, isPlaceholderData); the panel keeps rows mounted, marks the listbox aria-busy, and shows an inline updating spinner.
• Client: useSidebarThreadSearch defers leaving search mode to after the tap commit paints (rAF + macrotask), cancellable on re-activation and unmount.

How you verified

• New tests (fail before, pass after): apps/server/test/threads/thread-change-metadata.test.ts (row equals the bootstrap row; title/pin changes carry rows; created/plain events do not; missing thread keeps metadata), apps/server/test/public/public-sidebar-bootstrap-etag.test.ts (ETag headers, 304, rotation after change, If-None-Match matcher), apps/server/test/app/hub.test.ts (enricher gate on subscribers), packages/domain/test/change-kinds.test.ts (maximal fixture + lenient drop of unparseable row), apps/app/src/hooks/realtime-cache-effects.test.ts (7 patch/fallback cases with a real QueryClient), apps/app/src/components/sidebar/SidebarThreadSearchPanel.test.tsx (rows keep DOM identity while updating; empty-state message), apps/app/src/components/sidebar/useSidebarThreadSearch.test.tsx (deferred flip; cancel on reopen).
• pnpm exec turbo run typecheck lint --filter=@bb/app --filter=@bb/server --filter=@bb/db --filter=@bb/domain (0 errors), typecheck for @bb/sdk, @bb/server-contract, @bb/templates, @get-bb/plugin-sdk (bundled d.ts regenerated and checked).
• Full @bb/server suite: 1734 passed; the 2 failures are unrelated and pre-exist on the clean base (internal-skill-trees file-mode 420 vs 436 umask on this machine; a 5 s timeout in plugin-service.test.ts that passes in isolation). @bb/domain, @bb/db, @get-bb/plugin-sdk, @bb/templates suites pass; @bb/app src/hooks, src/lib/ws, src/components/sidebar, src/components/layout pass (49 + 43 files).

Fixes: part of the mobile / iOS Safari performance program (verified sweep report in the bb thread; no single issue).

Stack context

Layer 23 of 28 in the bb/mobile-perf/* stack (bottom → top: quick wins first, big rocks last).

• Prerequisite (layer below): bb/mobile-perf/diff-and-file-preview (Fetch diff-card context on demand; virtualize and cap the file preview (G2, G3) #1901).
• Next layer: bb/mobile-perf/thread-bootstrap-include (Bundle per-thread reads into GET /threads/:id?include= and seed the caches (B5) #1903).
• Audit findings addressed: see title IDs. Review: approved-with-fixes; 1 review fix commit(s).
• Reviewer notes / follow-ups: E8 is implemented as 'defer the search-mode flip' only (rAF + setTimeout 0 after the tap commit); the audit's alternative 'keep the thread list mounted during search' was not done, | Sidebar search still invalidates the thread-search prefix on every patched status/title/pin change and every events-appended flush (B18 territory, out of scope here); with keepPrev
• Wire/contract: Server->browser/SDK only: ThreadChangeMetadata gains optional listEntry: ThreadListEntry (strict outgoing schema; lenient inbound schema uses .optional().catch(undefined) so an unparseable row drops to a refetch instead of dropping the message). GET /api/v1/sidebar-bootstrap adds ETag: W/"<sha1-base64url>", Cache-Control: private, no-cache and 304 on If-None-Match. @bb/db gains `getThr

AGENT GENERATED: by Claude Opus 5

[SawyerHood]

Parked for now: the maintainer plans to land layers 1–22 (#1880–#1901) first. This layer stays a draft until an iOS device/Simulator pass covers it (see the verification report in the bb thread). Do not merge yet.

[SawyerHood]

Closing: the maintainer decided to land only layers 1–22 of the mobile-perf stack (#1880–#1901). The branch stays on the remote for reference; it can be reopened and rebased later if the remaining big rocks (sidebar-bootstrap patching, thread bootstrap include=, composer draft push-down, timeline windowing, persisted cache, service worker) are picked up again.