perf(cache): bound reported-failures set and halve default in-process budget

src/lib/cache.ts

@@ -49,7 +49,7 @@ function readPositiveInt(name: string, fallback: number): number {
 // In-process budget. Entries are evicted least-recently-*used* (see getMemory),
 // so a hot key only leaves when a hotter one takes its place. The default is
 // generous because the layer exists to keep origin calls off the hot path.
-const MAX_MEMORY_ENTRIES = readPositiveInt("CACHE_MEMORY_MAX_ENTRIES", 2_000);
+const MAX_MEMORY_ENTRIES = readPositiveInt("CACHE_MEMORY_MAX_ENTRIES", 1_000);
 
 // Single-flight: a key being (re)computed is awaited by concurrent callers
 // instead of each starting its own `fn()` (cache-stampede protection).
@@ -62,9 +62,20 @@ const generations = new Map<string, number>();
 const MAX_GENERATION_ENTRIES = MAX_MEMORY_ENTRIES * 2;
 
 // Keys whose most recent background refresh failed, so a persistently broken
-// origin reports once instead of on every read of a hot key.
+// origin reports once instead of on every read of a hot key. Bounded so a
+// high-cardinality stream of failing keys can never grow this without limit.
+const MAX_REPORTED_FAILURES = 500;
 const reportedFailures = new Set<string>();
 
+function recordReportedFailure(key: string): void {
+	if (reportedFailures.has(key)) return;
+	if (reportedFailures.size >= MAX_REPORTED_FAILURES) {
+		const oldest = reportedFailures.values().next().value;
+		if (oldest !== undefined) reportedFailures.delete(oldest);
+	}
+	reportedFailures.add(key);
+}
+
 /** Drop a key from the in-process cache (used when an upstream value changes). */
 export function invalidateMemory(key: string): void {
 	generations.set(key, (generations.get(key) ?? 0) + 1);
@@ -180,7 +191,7 @@ export async function cached<T>(
 					// read: a broken origin would otherwise flood the log from a
 					// single hot key.
 					if (reportedFailures.has(key)) return;
-					reportedFailures.add(key);
+					recordReportedFailure(key);
 					logger.warn("[cache] background refresh failed", {
 						key,
 						error: String(error),