fix: ensure LRU cache items have minimum size of 1 to prevent unbounded growth (#89040)
### What?
Prevent LRU cache unbounded growth by requiring `calculateSize` to
return values > 0.
### Why?
When `calculateSize` returned 0 (e.g., for `null` values in the
filesystem route cache), items were never evicted because they didn't
contribute to `totalSize`. This caused unbounded memory growth when
handling dynamic routes like `/api/logs/[id]` where each unique ID
created a new cache entry with size 0.
### How?
1. **LRUCache now throws an error if size ≤ 0** - This catches bugs at
development time rather than silently masking them:
```typescript
if (size <= 0) {
throw new Error(
\`LRUCache: calculateSize returned ${size}, but size must be > 0. \` +
\`Items with size 0 would never be evicted, causing unbounded cache
growth.\`
)
}
```
2. **Fixed filesystem.ts** - Null entries (negative cache) now return
size 1 instead of 0:
```typescript
if (!value) {
// Null entries (negative cache) still need a non-zero size for LRU
eviction
return 1
}
```
3. **Fixed next-dev-server.ts** - Static paths cache now uses `|| 1`
instead of `?? 0`:
```typescript
return JSON.stringify(value.staticPaths)?.length || 1
```
next.js
9e5759de - fix: ensure LRU cache items have minimum size of 1 to prevent unbounded growth (#89040)
