[arkhindi12]

Context

Cache memory is lost on server-side rendering re-hydration, so each SSR pass re-queries contract metadata the previous request already had.

Adds the two helpers the issue asks for in src/lru-memo-cache.ts:

• serializeCache(): string — versioned JSON snapshot
• LruMemoCache.hydrateCache<K, V>(json): LruMemoCache<K, V> — rebuild from a snapshot

Three details that matter for the SSR case

Expiries are stored as absolute epoch-ms deadlines, not remaining TTLs. A snapshot that sits in a transport for ten minutes must not hand every entry a fresh lease on life — otherwise hydration quietly serves stale contract metadata, which is the exact problem this is meant to solve.

Entries are written oldest → newest. Replaying them in that order restores LRU recency, so eviction after hydration still drops the coldest entry instead of an arbitrary one.

Hit/miss counters are not serialized. They describe the process that produced the snapshot; carrying them across would make metrics() report hits this cache never served. A hydrated cache starts at zero and measuredSpeedupPercent back at null.

Robustness

hydrateCache throws RangeError — rather than returning a half-built cache — when:

• the input is not valid JSON, or not a plain object
• version is not LRU_CACHE_SNAPSHOT_VERSION (currently 1)
• maxEntries is not a positive integer, or ttlMs is present but invalid
• entries is missing, or an entry has no key / a non-finite expiresAt

Entries already expired at hydration time are dropped. A snapshot claiming more entries than maxEntries keeps the newest ones, which is what replaying in order would have produced anyway.

Tests

src/tests/lru-memo-cache.test.ts — 9 new cases, 17 total in the file, all passing:

npx vitest run src/tests/lru-memo-cache.test.ts
 Test Files  1 passed (1)
      Tests  17 passed (17)

Covered: round-trip, recency order preserved through eviction, absolute expiry (400ms of a 1000ms TTL remains after a 600ms gap — not a fresh 1000ms), expired-in-transit entries dropped, default ttlMs carried across, metrics zeroed, unsupported version rejected, malformed snapshots rejected, over-long snapshot truncated to maxEntries.

tsc --noEmit reports no errors in lru-memo-cache.ts.

Note: the repo has pre-existing failures in custom-fetch*.test.ts, soroban-retry-after.test.ts, streams.test.ts and relayer-stress.test.ts (17 tests). Verified via git stash that they fail identically on a clean main, so they are unrelated to this change.

On assignment

I applied to this issue but haven't been assigned yet. Opening this as a draft so the approach is reviewable and the code is ready if you assign it — happy to close it without ceremony if you give this to someone else. If you'd rather review before any branch exists, say so and I'll take it down.

Closes #977

[arkhindi12]

Closing this — #977 is already implemented on main (merged in #1007, which I opened on Oct 18). I didn't check before opening this branch, so it's a duplicate of my own work and now conflicts.

Sorry for the noise. Nothing to review here.