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VerseVDI-Data-Plane/openspec/changes/phase3c-gateway-qualification/design.md
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Context

P3C-029 through P3C-033 require raw, reproducible processing, payload-rate, fairness, cap, and impairment evidence. Existing focused tests cover the framer, bounded queues, native Apollo fake, and fair pacer, but do not emit the normative ten-minute or six-profile artifacts.

Goals / Non-Goals

Goals:

  • Run the three 20/50/80 Mbps encoded-payload profiles for ten wall-clock minutes each after a recorded warm-up.
  • Measure the existing gateway framing path with a monotonic clock and retain compressed raw latency samples plus full summary statistics.
  • Run the exact six Section 7.2 configurations once using a deterministic, bounded virtual packet discipline and retain configured and observed values.
  • Exercise one real mTLS/QUIC fake-provider traversal for every media profile and reuse the real fair-pacer implementation for fairness and cap evidence.

Non-Goals:

  • Live Apollo/macOS/firewall qualification, real encoder fidelity, codec processing, host network mutation, or multi-host scale.
  • A production impairment framework, new gateway API, dependency, cgo, or sidecar.

Decisions

  • Implement the harness as an opt-in go test in package gateway. This keeps qualification access to the actual unexported fair pacer without adding a production API. Normal suites skip the long run unless an explicit absolute evidence directory is supplied.
  • Use wall-clock duration and target-rate pacing for performance profiles. Measure only receive-to-framed-payload processing; pacing wait and raw-file writes stay outside the measured interval and are reported separately.
  • Stream every raw sample into gzip-compressed CSV while retaining one bounded duration slice per profile for exact percentiles.
  • Use a fixed-seed virtual FIFO for impairment. It records no host claim and identifies its queue discipline and deterministic topology explicitly.
  • Treat any payload mutation, p95 above 5 ms, catalog mismatch, fairness error above 10%, cap excess above 5%, or step convergence beyond ten seconds as a hard command failure.

Risks / Trade-offs

  • [Local virtual impairment cannot prove deployed route behavior] → label every artifact deterministic and retain live Apollo/macOS/firewall as deferred-owner-e2e.
  • [Raw samples can be large] → stream gzip output and bound in-memory samples to the exact profile packet budget.
  • [Host load can invalidate latency] → record OS, architecture, Go version, timing overhead, actual duration, packet count, and observed bitrate; fail rather than substitute configured capacity for measured egress.