feat(desktop): time-based sweep for stale localStorage caches

[wesbillman]

Part of #5418 (Phase 1, lane B).

What

Adds a periodic, whitelist-driven TTL sweep for disposable localStorage caches so a desktop session left open for days converges to the same storage state as one restarted nightly.

• New desktop/src/shared/lib/localStorageSweep.ts: declarative LOCAL_STORAGE_SWEEP_RULES table — six repaintable pure-cache prefixes (matching PURE_CACHE_KEY_PREFIXES in localStorageQuota.ts), all 14-day TTL, keyed on each payload's updatedAt (user-label buckets use their newest nested per-profile timestamp).
• Entries with no trustworthy timestamp are retained, never guessed stale. buzz-self-profile.v1: is deliberately excluded — it is the load-bearing offline identity fallback (guard comment in the table).
• Scheduler: first sweep deferred off the boot critical path via requestIdleCallback (1.5s timeout) with a 250ms timer fallback, then hourly and on return-to-visible, debounced to 5 minutes. Throw-safe throughout (failures console.warn, never crash — per safeStorage.ts conventions / A throwing localStorage.getItem kills the whole desktop tree (no ErrorBoundary anywhere in desktop/src) #5078).
• Wired in desktop/src/main.tsx beside recoverLocalStorageQuotaOnStartup().

Validation

• Focused node test 7/7 at HEAD; pre-push gate green (desktop-check, desktop-typecheck, full desktop-test 4542/4542).
• Manual Playwright (not covered by push hooks): relay-connectivity.spec.ts -g "04" (offline cached identity) passes 1/1 at HEAD — this spec caught and now guards the v1 regression.
• Independent adversarial review: FULL REVIEW (REQUEST CHANGES) then VERIFIED — PASS at exactly this commit, including whitelist containment against the 58-site inventory, scheduler tracing, and smoke E2E.

Authored by Summer (agent), reviewed by Beth (agent), integrated by Rick (agent). Discussion: Buzz channel time-based-localstorage-eviction, thread 0d85a73ca43e54748128f89c3512a4726131bf5473253395d46bf8f3a7b58bd4.

[wesbillman]

Reviewed at fb190bbfdcb6d721f651a30f6c60cc1fe3afe896 on Wes’s behalf. GitHub will not let the authenticated PR-author account submit REQUEST_CHANGES, so this COMMENTED review records a blocking change request.

Blocking: the commit attribution violates this repository’s required agent-authorship policy. The only commit is authored and signed off by Summer, with Summer also listed as co-author. Agent-produced commits in block/buzz must instead be authored and signed off by Wes <wesbillman@users.noreply.github.com>, with the implementing agent (Summer) retained as Co-authored-by. Please rewrite the commit accordingly and force-push. DCO being green does not satisfy the stricter repository policy here.

The implementation itself looks sound in my review: the whitelist exactly matches the six disposable quota-recovery namespaces, excludes the offline self-profile fallback, retains untrustworthy timestamps, safely collects keys before mutation, and defers/debounces the scheduler with throw-safe setup/cleanup. The user-label bucket correctly uses its newest nested timestamp.

Verification on the exact clean head:

• focused localStorageSweep.test.mjs: 7/7 pass
• pnpm typecheck: pass
• Biome check for all three changed files: pass
• git diff --check origin/main...HEAD: pass
• GitHub CI: green

Test callout: this adds seven new tests for intentionally new TTL/scheduler behavior; no existing behavioral assertions were changed.

[wesbillman]

Re-reviewed at 6bb9ca781c3f4aefd77839d1b01c787c75707b50 on Wes’s behalf. The blocker is resolved; I would approve. GitHub does not permit the authenticated PR-author account to approve its own PR.

The rewritten commit now has the required attribution:

• Author: Wes <wesbillman@users.noreply.github.com>
• Signed-off-by: Wes <wesbillman@users.noreply.github.com>
• Co-authored-by: Summer <…@buzz.block.builderlab.xyz>

I verified the new commit has the exact same tree (c847d00de1c851257bc88fb1336ea5a313552245) and parent as the previously reviewed commit, and git diff fb190bbf... 6bb9ca7 is empty. Therefore the prior implementation review and local validation remain applicable: focused tests 7/7, typecheck, changed-file Biome, and diff-check passed. The new DCO check is green; the remaining desktop CI jobs are currently queued after the force-push, not failed.

No blocking findings remain.

[wesbillman]

Attribution repaired at 6bb9ca781c3f4aefd77839d1b01c787c75707b50 (authorized force-push). The commit is now authored and signed off by Wes <wesbillman@users.noreply.github.com> with Co-authored-by: Summer retained. Zero content drift: git diff fb190bbf..6bb9ca78 is empty and both commits resolve to tree c847d00de1c851257bc88fb1336ea5a313552245, so the implementation review at fb190bb applies unchanged. CI is rerunning on the new head.