resid pt 3: friendship checks & auth session reads

.env.example

@@ -18,6 +18,8 @@ CACHE_KEY_PREFIX=friendolls
 CACHE_DEFAULT_TTL_SECONDS=60
 CACHE_MAX_TTL_SECONDS=86400
 CACHE_METRICS_LOG_INTERVAL_MS=60000
+# Max number of cache keys tracked per invalidation tag
+CACHE_TAG_MAX_ENTRIES=5000
 
 # JWT Configuration
 JWT_SECRET=replace-with-strong-random-secret