fix(web): reset scroll restoration when sessionStorage quota hits

[heavygee]

Summary

• TanStack Router keeps scroll restoration state in memory; when sessionStorage.setItem failed we could prune the JSON on disk but the in-RAM map stayed huge, so the very next scroll persist threw again and the UI still hit the error boundary (fix(web): TanStack scroll restoration fills sessionStorage and can crash the SPA #708).
• On any persist failure for tsr-scroll-restoration-v1_3, after prune+retry fails (or JSON is invalid), clear storage and call scrollRestorationCache.set(() => ({})) when the guarded target is real window.sessionStorage (skipped in unit tests that use a mock Storage).
• Treat any write failure on that key as recoverable (not only QuotaExceededError / DOMException-shaped quota errors).

Test plan

• cd web && bun run test src/lib/scrollStorageGuard.test.ts (11 tests)
• cd web && bun run typecheck
• Manual: long session chat, scroll, navigate until storage is stressed; confirm no uncaught setItem / no white-screen error boundary

Issues

Fixes #708

[github-actions]

Findings

• [Major] Successful prune still leaves TanStack cache oversized — when the trimmed retry succeeds, the persisted JSON shrinks but scrollRestorationCache keeps the full in-memory map, so the next TanStack persist serializes the huge state again and re-enters the quota path. Evidence web/src/lib/scrollStorageGuard.ts:102.
• [Major] Hard reset can recurse through the guarded setter — scrollRestorationCache.set persists through sessionStorage.setItem, which is already replaced by wrappedSetItem; if even the {} write fails, it re-enters the same hard-reset path until stack overflow. Evidence web/src/lib/scrollStorageGuard.ts:36.

Summary

• Review mode: initial
• The patch does not fully clear TanStack Router memory on the common successful-prune path, and the failure reset path can recursively call itself.
• Coverage gap: tests use a mock Storage, so they skip the real-sessionStorage cache reset branch.

Testing

• Not run (automation): bun is not installed in this runner.

HAPI Bot

[github-actions]

Findings

• [Major] Successful prune still leaves TanStack cache oversized — the new hard reset only runs when parsing or the trimmed retry fails, but when originalSetItem accepts the trimmed JSON the closed-over scrollRestorationCache.state remains the full oversized object. TanStack’s next scroll update mutates and serializes that same large state again, so the UI can hit the same storage exception immediately after a “successful” recovery. Evidence web/src/lib/scrollStorageGuard.ts:102.
• [Major] Hard reset can recurse through the guarded setter — scrollRestorationCache.set(() => ({})) writes via the captured sessionStorage.setItem, which is already replaced by wrappedSetItem; if the {} write throws, the wrapper re-enters hardResetScrollRestorationPersistedState before the fallback can run. Evidence web/src/lib/scrollStorageGuard.ts:36.

Summary

• Review mode: follow-up after new commits
• The follow-up added tests, but the production guard still has the two failure modes from the previous bot review. The current tests mock scrollRestorationCache.set as a pure function, so they do not exercise TanStack’s real setter writing back through sessionStorage.setItem.

Testing

• Not run (automation): bun is not installed in this runner.

HAPI Bot

[github-actions]

Findings

• None.

Summary

• Review mode: follow-up after new commits
• No issues found in the latest PR diff. The previous two bot findings are addressed in web/src/lib/scrollStorageGuard.ts: the successful prune path now syncs TanStack's in-memory cache, and cache writes temporarily restore the original setItem to avoid recursive guarded writes. Residual risk: this still depends on TanStack Router's private tsr-scroll-restoration-v1_3 storage key and scrollRestorationCache internals.

Testing

• Not run (automation): bun is not installed in this runner.
• Reviewed contributor-reported coverage in web/src/lib/scrollStorageGuard.test.ts for successful prune cache sync and unwrapped hard reset writes.

HAPI Bot