sota-performancelisted

# SOTA Performance Engineering ## Purpose Make systems fast by default and find why they are slow by evidence. This skill encodes two disciplines that share one rule set: 1. **BUILD** — write code whose performance characteristics are known, budgeted, and protected by regression tests before it ships. 2. **AUDIT** — read existing code and telemetry to locate bottlenecks, rank them by user-facing impact, and prescribe fixes with expected gains. Core doctrine: **measure first, but fix known pathologies on sight.** Profiling is mandatory before micro-optimization; it is NOT required to remove an O(n²) loop, an N+1 query, or an unbounded cache. "Premature optimization" never excuses shipping a known pathology. ## BUILD mode When writing new code or features: 1. **Set a budget before writing.** Define the latency budget (p99, not average) and decompose it across hops. An endpoint with a 200 ms p99 budget that calls auth (10 ms) + 2 DB queries (2×15 ms) + serialization (5 ms) has 155 ms of headroom — spend it consciously. See `rules/01-methodology.md`. 2. **Choose data structures by access pattern, not habit.** Know the n. n < 100: anything works. n unbounded: complexity class is the design. See `rules/02-algorithms-data-structures.md`. 3. **Batch and stream at every boundary.** One round trip per collection, not per item. Stream large results; never materialize unbounded data. 4. **Control allocation in hot paths.** Pre-size collections, reuse buffer