fix(cache): add structured debug log for each cache eviction (#737)

Emit a debug-level structured log on every in-memory cache eviction with
the fields required by the acceptance criteria:

- cache_key: the evicted entry's key
- reason: 'ttl_expired' or 'capacity_overflow'
- cache_size_after: map size read after the delete call
- evicted_at: ISO 8601 timestamp at eviction time

The stale-on-read path in getCachedCreatorList is a TTL expiry variant
and now logs with reason 'ttl_expired' instead of the previous 'stale'.
The delete is performed before the log call so cache_size_after reflects
the post-eviction size as specified.

Author: Alaka-ibr

src/modules/creators/creators-cache-eviction-log.test.ts

@@ -0,0 +1,180 @@
+import {
+   getCachedCreatorList,
+   setCachedCreatorList,
+   resetCreatorListCache,
+} from './creators.cache';
+import { logger } from '../../utils/logger.utils';
+
+jest.mock('../../utils/logger.utils', () => ({
+   logger: {
+      debug: jest.fn(),
+      info: jest.fn(),
+      warn: jest.fn(),
+      error: jest.fn(),
+      isLevelEnabled: jest.fn().mockReturnValue(true),
+   },
+}));
+
+jest.mock('../../constants/creator-public-cache.constants', () => ({
+   CREATOR_PUBLIC_ROUTE_CACHE_MAX_AGE_SECONDS: { publicRead: 60 },
+}));
+
+const mockLogger = logger as unknown as {
+   debug: jest.Mock;
+};
+
+const BASE_QUERY = {
+   limit: 20,
+   offset: 0,
+   sort: 'createdAt' as const,
+   order: 'desc' as const,
+   include: [] as never[],
+};
+
+function findEvictionCalls(): Record<string, unknown>[] {
+   return mockLogger.debug.mock.calls
+      .map((args: unknown[]) => args[0] as Record<string, unknown>)
+      .filter(
+         (obj: Record<string, unknown>) =>
+            obj.event === 'creator_list_cache_eviction'
+      );
+}
+
+describe('cache eviction structured log (#737)', () => {
+   beforeEach(() => {
+      jest.clearAllMocks();
+      resetCreatorListCache();
+   });
+
+   describe('TTL expiry', () => {
+      it('emits a debug log with reason ttl_expired when a stale entry is read', () => {
+         setCachedCreatorList(BASE_QUERY as any, [], 0);
+
+         jest.spyOn(Date, 'now').mockReturnValue(Date.now() + 120_000);
+
+         getCachedCreatorList(BASE_QUERY as any);
+
+         const evictions = findEvictionCalls();
+         const ttlEviction = evictions.find(
+            (e) => e.reason === 'ttl_expired'
+         );
+
+         expect(ttlEviction).toBeDefined();
+         expect(ttlEviction).toHaveProperty('cache_key');
+         expect(ttlEviction).toHaveProperty('reason', 'ttl_expired');
+         expect(ttlEviction).toHaveProperty('cache_size_after');
+         expect(ttlEviction).toHaveProperty('evicted_at');
+
+         jest.restoreAllMocks();
+      });
+
+      it('cache_size_after reflects the size after eviction', () => {
+         setCachedCreatorList(BASE_QUERY as any, [], 0);
+
+         jest.spyOn(Date, 'now').mockReturnValue(Date.now() + 120_000);
+
+         getCachedCreatorList(BASE_QUERY as any);
+
+         const evictions = findEvictionCalls();
+         const ttlEviction = evictions.find(
+            (e) => e.reason === 'ttl_expired'
+         );
+
+         expect(ttlEviction!.cache_size_after).toBe(0);
+
+         jest.restoreAllMocks();
+      });
+
+      it('evicted_at is a valid ISO 8601 timestamp', () => {
+         setCachedCreatorList(BASE_QUERY as any, [], 0);
+
+         jest.spyOn(Date, 'now').mockReturnValue(Date.now() + 120_000);
+
+         getCachedCreatorList(BASE_QUERY as any);
+
+         const evictions = findEvictionCalls();
+         const ttlEviction = evictions.find(
+            (e) => e.reason === 'ttl_expired'
+         );
+         const parsed = new Date(ttlEviction!.evicted_at as string);
+
+         expect(parsed.toISOString()).toBe(ttlEviction!.evicted_at);
+
+         jest.restoreAllMocks();
+      });
+
+      it('log level is debug', () => {
+         setCachedCreatorList(BASE_QUERY as any, [], 0);
+
+         jest.spyOn(Date, 'now').mockReturnValue(Date.now() + 120_000);
+
+         getCachedCreatorList(BASE_QUERY as any);
+
+         const evictions = findEvictionCalls();
+
+         expect(evictions.length).toBeGreaterThanOrEqual(1);
+         expect(mockLogger.debug).toHaveBeenCalled();
+
+         jest.restoreAllMocks();
+      });
+   });
+
+   describe('capacity overflow', () => {
+      it('emits a debug log with reason capacity_overflow when the cache exceeds max entries', () => {
+         for (let i = 0; i < 252; i++) {
+            const query = { ...BASE_QUERY, offset: i };
+            setCachedCreatorList(query as any, [], 0);
+         }
+
+         const evictions = findEvictionCalls();
+         const overflowEviction = evictions.find(
+            (e) => e.reason === 'capacity_overflow'
+         );
+
+         expect(overflowEviction).toBeDefined();
+         expect(overflowEviction).toHaveProperty('cache_key');
+         expect(overflowEviction).toHaveProperty(
+            'reason',
+            'capacity_overflow'
+         );
+         expect(overflowEviction).toHaveProperty('cache_size_after');
+         expect(overflowEviction).toHaveProperty('evicted_at');
+      });
+
+      it('cache_size_after reflects the size after the overflow eviction', () => {
+         for (let i = 0; i < 252; i++) {
+            const query = { ...BASE_QUERY, offset: i };
+            setCachedCreatorList(query as any, [], 0);
+         }
+
+         const evictions = findEvictionCalls();
+         const overflowEvictions = evictions.filter(
+            (e) => e.reason === 'capacity_overflow'
+         );
+
+         for (const eviction of overflowEvictions) {
+            expect(
+               typeof eviction.cache_size_after === 'number'
+            ).toBe(true);
+            expect(
+               (eviction.cache_size_after as number) <= 250
+            ).toBe(true);
+         }
+      });
+
+      it('evicted_at is a valid ISO 8601 timestamp on overflow eviction', () => {
+         for (let i = 0; i < 252; i++) {
+            const query = { ...BASE_QUERY, offset: i };
+            setCachedCreatorList(query as any, [], 0);
+         }
+
+         const evictions = findEvictionCalls();
+         const overflowEviction = evictions.find(
+            (e) => e.reason === 'capacity_overflow'
+         );
+         const parsed = new Date(overflowEviction!.evicted_at as string);
+
+         expect(parsed.toISOString()).toBe(overflowEviction!.evicted_at);
+      });
+   });
+});

src/modules/creators/creators.cache.ts

@@ -29,15 +29,15 @@ function getCreatorListCacheTtlMs(): number {
 function pruneCreatorListCache(now: number): void {
    for (const [cacheKey, entry] of creatorListCache.entries()) {
       if (entry.expiresAt <= now) {
+         creatorListCache.delete(cacheKey);
          logger.debug({
             msg: 'Creator list cache eviction',
             event: 'creator_list_cache_eviction',
-            cacheKey,
-            reason: 'expired',
-            expiresAt: entry.expiresAt,
-            now,
+            cache_key: cacheKey,
+            reason: 'ttl_expired',
+            cache_size_after: creatorListCache.size,
+            evicted_at: new Date(now).toISOString(),
          });
-         creatorListCache.delete(cacheKey);
       }
    }
 
@@ -51,15 +51,15 @@ function pruneCreatorListCache(now: number): void {
       .slice(0, overflow);
 
    for (const [cacheKey] of oldestEntries) {
+      creatorListCache.delete(cacheKey);
       logger.debug({
          msg: 'Creator list cache eviction',
          event: 'creator_list_cache_eviction',
-         cacheKey,
-         reason: 'overflow',
-         cacheSize: creatorListCache.size,
-         maxSize: MAX_CREATOR_LIST_CACHE_ENTRIES,
+         cache_key: cacheKey,
+         reason: 'capacity_overflow',
+         cache_size_after: creatorListCache.size,
+         evicted_at: new Date(now).toISOString(),
       });
-      creatorListCache.delete(cacheKey);
    }
 }
 
@@ -117,15 +117,15 @@ export function getCachedCreatorList(
    }
 
    if (cachedEntry) {
+      creatorListCache.delete(cacheKey);
       logger.debug({
          msg: 'Creator list cache eviction',
          event: 'creator_list_cache_eviction',
-         cacheKey,
-         reason: 'stale',
-         expiresAt: cachedEntry.expiresAt,
-         now,
+         cache_key: cacheKey,
+         reason: 'ttl_expired',
+         cache_size_after: creatorListCache.size,
+         evicted_at: new Date(now).toISOString(),
       });
-      creatorListCache.delete(cacheKey);
    }
 
    pruneCreatorListCache(now);