perf-optimization

Profile-driven performance optimization of mecatl using the offline benchmark + scenario harness. Use when optimizing allocations or latency, reducing allocs/op or memory, profiling a Go benchmark, pinpointing a hotspot with pprof, proving a win with benchstat, adding a regression benchmark, wiring profile-guided optimization (PGO), or investigating "why is this slow / allocating" or a suspected perf regression. Covers task bench, task perf:scenarios, memprofile -> pprof, benchstat A/B, allocs-first gating, PGO setup, and the discipline (follow the profile not the hypothesis; keep pure-perf changes byte-identical; mutation-test cache guards; skip the wrong abstraction). NOT for the live perf MCP server (use perf-mcp-interpretation) or non-mecatl Go profiling.