LowFile-scopeC# Plug & play

Use HashSet for fast membership checks

Use HashSet<T> for repeated contains checks on large collections.

Why this matters

Provides O(1) average membership checks vs O(n) scans.

Side-by-side examples engineers can pattern-match during review.

Avoid

if (list.Contains(id)) { /* ... */ }

Prefer

if (set.Contains(id)) { /* ... */ }

Bad

list.Contains(x)

Good

hashSet.Contains(x)

From the same buckets as this rule.

Critical
Avoid Blocking Calls to Async Methods
Blocking async methods with `.Result` or `.Wait()` can cause deadlocks and prevent efficient asynchronous execution. Use `await` instead for proper async behavior.
concurrency-safetyperformance-efficiency
Critical
Fingerprint assets and cache immutably
All static JS/CSS/font/image files MUST use content-hashed filenames (e.g., app.9c1a7b.js) and be served with "Cache-Control: public, max-age=31536000, immutable". HTML and other non-fingerprinted documents MUST be served with "Cache-Control: no-cache" (or equivalent) to enable conditional revalidation.
web-static-assetscaching-strategy+2
Critical
No live network or DB in unit tests—use fakes/mocks
Unit tests must stub or fake external HTTP/DB calls; allow real I/O only in integration/e2e tests tagged accordingly.
testing-qualityperformance-efficiency+1