Wrapping an SDK directly buys you three walls within months: usage fields that don't agree, error semantics tied to SDK exception types, and tool-call formats that change per provider. All five reference projects separate 'wire protocol' from 'provider identity' as independent dimensions. Rivumi goes further with pydantic canonical contracts (Message/ToolCall/Usage/ModelTurn) plus six protocol adapters, forces the OpenAI SDK's built-in retries to zero, and routes every failure through a classified ProviderErrorKind before any retry policy sees it. Its provider table is deliberately copied from pi's packages/ai — lineage, not coincidence.
Intermittent NVIDIA NIM 500s exposed Rivumi's early gap: classified errors with no retry consumer. SDK retries are now disabled; the harness gives each candidate up to five attempts with jittered exponential backoff and capped Retry-After handling, then can move to an explicitly configured fallback model. Both model.retry and model.fallback enter the event log.
The ecosystem treats /v1/chat/completions as the lingua franca, but your providers don't all speak it. The five reference projects split into three camps: pi and OpenCode make the client speak every dialect natively so no gateway is needed; OMP builds a real protocol translator (foreign wire → neutral context → provider adapter, no raw passthrough); Codex and Claude Code run proxies that translate nothing and exist purely to force traffic through a controllable path. Rivumi copies OMP's boundary but narrows it to one wire in, one out: strictly parse OpenAI Chat into a canonical contract, then dispatch to any ModelProvider — and along the way hit a cross-event-loop client-close bug whose lesson is that provider lifecycles belong to the ASGI lifespan, not the signal handler.
Small models don't fail at reasoning first — they fail at format stability: tool-call JSON, diff hunk arithmetic, and context budgets all break. The mature harnesses build evals on real model behavior (pi's model-backed evals, OMP calibrating benchmarks from real session logs, Codex even relaxing its parser for weaker models). rivumi picks the narrowest but hardest path: one fixture, five real Ollama runs, a manifest declaring exactly which files and patch fragments count as success — and M2's failure kept verbatim as evidence. Never pass mock off as E2E; never spin partial success into full passes.
The five reference projects split into three camps on subscription auth. Codex and Claude Code implement OAuth only for their own official clients and store tokens in the OS keyring. pi and OMP directly reuse Claude Code's client ID to implement Pro/Max OAuth — technically feasible, but Anthropic's docs explicitly bar third parties from offering claude.ai login without approval. OpenCode removed its bundled Pro/Max plugins entirely, the cleanest policy precedent in the ecosystem. Rivumi's rules: own your grant, never scrape another CLI's credentials, accept third-party OAuth only when the provider clearly supports it, and never copy or forward credentials.
None of the five reference projects enforces 'all declared verification commands pass' at the harness level: pi leaves verification to the model, OpenCode and Codex put it in the system prompt, Claude Code uses a separate adversarial verifier subagent but as a soft contract, and only OMP's cleanse actually runs checks from harness code. rivumi takes the hardest path: if files changed, every declared verification command must pass before terminal_reason=verified; with no changes, checks don't rerun (no_changes). Whether to verify is decided by code, not by the model.