reliability: In-memory caches grow unbounded (priceCache, keyCache)

[moltboie]

Problem

Two in-memory Map caches check TTL on read but never evict stale entries:

priceCache (polygon.ts:29)

const priceCache = new Map<string, { price: number; fetchedAt: number }>();

Keys are ${ticker}:${dateString}. With daily syncs across multiple tickers and date lookups, entries accumulate indefinitely. Old entries (past TTL) are never read again but never deleted.

keyCache (webhook.ts:5)

const keyCache = new Map<string, { key: jose.JWK; fetchedAt: number }>();

Plaid rotates verification keys. Old key IDs will never be used again but entries persist forever.

Impact

• Low severity in practice (small data per entry, server restarts clear them)
• But it's unbounded growth in a long-running process — against clean code principles
• Compare with rate-limit.ts which correctly cleans up stale records on a timer

Fix

Add periodic eviction (like rate-limit's cleanup):

const evictStaleEntries = () => {
  const now = Date.now();
  for (const [key, entry] of priceCache) {
    if (now - entry.fetchedAt >= CACHE_TTL_MS) priceCache.delete(key);
  }
};
setInterval(evictStaleEntries, CACHE_TTL_MS);

Or use a simple LRU approach with a max size cap.