Archestra LLM Providers & Proxy

Use this skill before adding an LLM provider or changing provider translation, streaming, or model handling. Run commands from platform/ unless specifically instructed otherwise.

Provider surface map

One provider touches all of these (use github-copilot as the worked example — it is OpenAI-compatible, so it follows the default path; microsoft-365-copilot is the most recent full addition and shows the harder shape, with its own graph translator):

• backend/src/types/llm-providers/<provider>/ — api.ts, messages.ts, tools.ts, index.ts (some also have models.ts). index.ts default-exports a namespace (e.g. GithubCopilot) with API/Messages/Tools plus a Types sub-namespace; register it in types/llm-providers/index.ts. OpenAI-compatible providers re-export OpenAI schemas with .passthrough().
• backend/src/routes/proxy/adapters/<provider>.ts — exports <provider>AdapterFactory; re-export it from adapters/index.ts.
• backend/src/routes/proxy/routes/<provider>.ts — Fastify plugin: fastifyHttpProxy catch-all with createProxyPreHandler (from proxy-prehandler.ts), explicit POST .../chat/completions handlers (default-agent and :agentId variants) calling handleLLMProxy, and model-listing GETs via proxy-model-listing.ts. Register the plugin in BOTH places: re-export it from backend/src/routes/index.ts (the main API surface iterates Object.values(routes)) AND add it to registerWorkerRoutes in server.ts.
• shared/model-constants.ts — add to SupportedProvidersSchema, SupportedProvidersDiscriminatorSchema (<provider>:chatCompletions for OpenAI-compatible; others name their API shape, e.g. anthropic:messages, bedrock:converse), and providerDisplayNames. Membership in PROVIDERS_WITH_OPTIONAL_API_KEY, PROVIDERS_REQUIRING_BASE_URL, and PROVIDERS_REQUIRING_PER_USER_CREDENTIAL silently changes auth behavior: per-user-credential providers get personal-scope keys only, no team/org/env fallback (see the github-copilot rationale comment there).
• backend/src/routes/chat/model-fetchers/ — add a fetcher and register it in the modelFetchers record in model-fetchers/index.ts; its Record<SupportedProvider, ModelFetcher> type makes a missing provider a compile error. registry.ts#testProviderApiKey uses it to validate keys on creation. Simple bearer /models endpoints reuse makeBearerFetcher/makeStaticFetcher from bearer-fetcher.ts.
• Message normalization for the chat feature lives in backend/src/routes/chat/normalization/ (notably prepare-for-provider.ts) and prepare-model-messages.ts — provider-specific message-shape rules go here, not in the proxy adapters.
• Frontend: provider key management at frontend/src/app/llm/model-providers/page.tsx + frontend/src/components/create-llm-provider-api-key-dialog.tsx; provider icon at frontend/public/icons/<provider>.png; model pickers (components/llm-model-select.tsx, components/chat/model-selector.tsx) use providerDisplayNames.
• Also: backend/src/config.ts + .env.example for base-URL/key env vars, ../docs/pages/platform-supported-llm-providers.md.

Default path: OpenAI-compatible

• Most new providers are OpenAI-compatible. Do not hand-roll a translator: call createOpenAiCompatibleAdapterFactory from adapters/openai-compatible-adapter.ts with provider, interactionType, getBaseUrl, and createClient — it reuses OpenAIRequestAdapter/OpenAIResponseAdapter/OpenAIStreamAdapter wholesale. See adapters/deepseek.ts (minimal) and adapters/github-copilot.ts (custom auth via a fetch wrapper, since createClient is synchronous).
• Providers with genuinely different wire formats get translator modules next to the adapter (gemini-openai-translator.ts, bedrock-openai-translator.ts, cohere-openai-translator.ts, anthropic-openai-translator.ts) — fix translation bugs there, with a matching *.test.ts.

Guard rails

• backend/src/routes/proxy/routes/provider-matrix.test.ts — providerConfigsByProvider is satisfies Record<SupportedProvider, ProviderTestConfig>, so adding a provider to the enum without a matrix entry (route plugin + adapter factory + endpoints) fails typecheck. The suite then exercises every provider's real route with a mocked client: declared-tool persistence, execution IDs, streaming tool calls, cost-optimized model substitution, TOON compression, and limit blocking.
• The modelFetchers record (above) enforces the same exhaustiveness for model listing.

Translation gotchas (real handling, check before "fixing")

• Empty assistant turns: convertToModelMessages can produce assistant messages with empty content that providers reject. buildModelMessagesForProvider in routes/chat/prepare-model-messages.ts filters them (isEmptyAssistantModelMessage) and then repairs unanswered tool calls (ensureToolCallsHaveResults) so tool_use/tool_result adjacency holds. The Cohere proxy adapter (adapters/cohere.ts) does its own empty-assistant filtering.
• Tool-call name repair: harmony-format models leak reasoning-channel sentinels into tool names (name<|channel|>commentary). routes/chat/tool-call-repair.ts#repairHarmonyToolName strips them, gated on an exact match against registered tools; wired via experimental_repairToolCall in routes/chat/routes.ts.
• Provider message-shape rules: Gemini and Bedrock require the first non-system turn to be from the user — ensureLeadingUserTurn in prepare-model-messages.ts prepends one for both (the provider set gating it lives next to the function). Bedrock content rules (every message non-empty, user messages need a text part) are enforced in normalization/prepare-for-provider.ts (ensureBedrockMessageHasContent, ensureBedrockUserMessageHasTextPart); the same file decides per provider whether text documents stay native document blocks (Anthropic/Bedrock) or are inlined as decoded text (everyone else).
• Output-token ceilings: agents/agent-output-budget.ts#resolveAgentMaxOutputTokens clamps maxOutputTokens to the model's real output limit from model metadata (sanitizeOutputLimit from clients/models-dev-client.ts, 8192 fallback) and the operator ceiling — don't hardcode max-token values.

Validation

cd backend && npx vitest run src/routes/proxy/routes/provider-matrix.test.ts
cd backend && npx vitest run src/routes/proxy/adapters/<provider>*.test.ts   # adapter/translator unit tests
pnpm type-check

• Manual end-to-end check: PROVIDER_SMOKE_TEST.md (repo root of platform/) is a browser-automation smoke runbook covering chat, policies, TOON, and proxy flows — run it after provider/proxy changes that unit tests can't cover.

Related skills

• archestra-dev-backend — general route/codegen/permission conventions (route shape, RouteId, endpoint permissions).
• archestra-dev-backend-tests — vitest projects, mocking rules, DB fixtures for the tests above.