v0.2.1 — HTTP overhead benchmarks

Summary

Interlock now publishes deployer-facing HTTP overhead numbers — not just engine microbenchmarks.

Headline: sub-millisecond engine overhead — ~0.5 ms on sensitive reads (typical agent traffic) and ~0.1 ms on sink checks.

Added

• End-to-end HTTP overhead benchmarks (A + C): TestHTTP_OverheadReport_* (p50/p95/p99/p999 histogram), BenchmarkHTTP_EngineDelta_* (engine on vs passthrough)
• make bench-http and CI smoke (OVERHEAD_SAMPLES=100)
• mcphttp.Client.CallDuration for client-perceived latency
• TestHTTP_ConcurrentLoad_KnownGap — concurrent multi-session load deferred (single canonical HTTP load gap)

Changed

• docs/performance.md — leads with engine delta (C), not absolute latency (A); explains taint-ingestion vs overlap delta inversion; secret-count scaling caveat

Removed

• TestBenchmark_FullHTTPLoad_KnownGap — duplicate gap documentation (superseded by TestHTTP_ConcurrentLoad_KnownGap)

Verify

git fetch --tags
git -c gpg.ssh.allowedSignersFile=allowed_signers tag -v v0.2.1

Full changelog: CHANGELOG.md