Benchee Profiling

Canonical FP bar: docs/fcis-engineering-rules.md — Functional Core, Imperative Shell: pure domain modules; side effects at edges. Measure pure functions and edge paths separately; keep benchmarks free of accidental I/O.

RULES — Follow these with no exceptions

1. Profile first — run :fprof or :eprof and verify the output explicitly names the expected slow call site; re-run with a larger workload if ambiguous 2. Write a comparative benchmark — implement at least 2 alternative approaches using Benchee, ensuring implementations do the same thing; benchmark in MIX_ENV=prod for realistic results 3. Use multiple inputs — test with small, medium, and large realistic data sizes to catch size-dependent behavior 4. Warm up before measuring — use warmup: 2 and time: 10; repeat 3–5 times to rule out variance; if results are within noise (< 5% difference), run 3 additional times 5. Validate improvement — confirm the faster approach wins across all input sizes 6. Save baseline and check regressions — write results to bench/baseline.json; raise an error if performance degrades more than 10% (compare against the previous 3 baselines before raising to rule out noise) 7. Separate I/O benchmarks — never benchmark network or disk I/O in the same run as compute benchmarks

Setup