Milestone 4.C.5 — Streaming Hardening

Status: Planned
Goal: Track C — Multi-Provider Adapters & Resilience
Phase: 4 — Operator Platform & Multi-Provider
Estimated effort: 2 days
Track: Track C — Multi-Provider Adapters & Resilience

Why This Milestone Exists

Multi-provider means multi-dialect failure modes. Anthropic emits error events mid-stream differently than OpenAI's connection-drop pattern. The proxy must handle slow-client backpressure (bounded buffer + timeout) and normalize mid-stream errors across providers to the same ADR-0027 verbatim-close behavior.

Orientation (indicative)

Named paths, package layouts, libraries, schemas, env vars, and commands anywhere on this page are rough sketches for orientation — inspiration and a baseline, not a required change list.

During implementation, expect to:

open the live tree and follow existing patterns before inventing new ones
research current constraints (latency, tenancy, deploy shape, libraries) more deeply than this page can
advance the design beyond the sketch where measurement or code reality says so
land work in different filenames, merged packages, deferred docs, or new surfaces when the situation calls for it

Prefer outcomes over matching any particular file tree or command sequence.

Areas that may be involved (situational — not a checklist):

Provider abstraction / adapters
Proxy service (HTTP, bootstrap, config)

Success signals

Outcome-oriented signals that the milestone is in good shape. Exact filenames, package layouts, and commands may differ from any sketches above.

Slow-client backpressure test: client reads 1 byte/sec, proxy does not buffer unbounded upstream data (bounded buffer + timeout, then close upstream)
Mid-stream Anthropic error event and mid-stream OpenAI connection drop both produce the same client-visible behavior (verbatim close per ADR-0027)
No memory leak under sustained slow-client load (verified via benchmark)
Both providers tested with the same parameterized test harness

Prerequisites

Milestone 4.C.1 (Anthropic adapter hardening)
ADR-0027 (streaming behavior specification)