BTerminal/.claude/rules/12-performance-awareness.md

paths
src/**/*.{ts,js,py,go,rs,dart,kt,java} lib/**/*.{ts,js,py,go,rs,dart,kt,java} app/**/*.{ts,js,py,go,rs,dart,kt,java}

Performance Awareness

Prevent anti-patterns that are expensive to fix later — not premature optimization.

Flag Proactively

• N+1 queries — fetching a list then querying individually per item.
• Unbounded fetches — no pagination or limits.
• O(n^2) when O(n) exists — nested loops, repeated scans, quadratic string building.
• Loading into memory — entire files/datasets when streaming is possible.
• Missing indexes — unindexed columns in tables expected to grow beyond 10k rows.
• Synchronous blocking — blocking event loop/main thread during I/O.
• Connection pool exhaustion — new connections per request instead of pooling.
• Unverified slow queries — use EXPLAIN/EXPLAIN ANALYZE; don't guess about indexes.

Rules

• Flag anti-patterns and offer to fix or create a TODO.
• Quantify: "loads ~10MB per request" not "might use a lot of memory."