pi_harness/packages/agent/docs/models.md

Models architecture

This document describes the target design for the next pi-ai model/provider refactor. It describes the desired shape, not the current implementation. It is intended to be complete enough to start implementing from a fresh session.

Goals:

• Models is a dumb runtime collection of providers.
• Concrete providers own metadata, auth, model listing, and stream behavior.
• API implementations live under src/api/ and are reusable/lazy.
• Concrete provider factories live under src/providers/.
• Users can import only the providers they need.
• Importing a provider must not eagerly import heavy SDKs.
• Dynamic model lists are first-class and side-effect-free.
• models.json and extensions layer by wrapping providers, not by mutating provider internals ad hoc.
• Old global APIs survive only in an explicit, temporary /compat entrypoint.

Non-goals for the immediate pi-ai pass:

• Do not migrate coding-agent ModelRegistry yet.
• Do not keep the stream/API registry inside Models.
• Do not implement web OAuth flows yet (the factory option is reserved).
• Images (images.ts, images-api-registry.ts) are out of scope; leave untouched.

Package layout

Target source layout:

packages/ai/src/
  index.ts                    # core exports only; no built-in provider imports
  models.ts                   # Models runtime, Provider, auth types
  compat.ts                   # temporary old-API compatibility entrypoint
  auth/                       # auth method types, helpers, login callbacks
  api/                        # API implementations and lazy wrappers
    openai-completions.ts     # real implementation, imports SDKs, exports stream/streamSimple
    openai-completions-lazy.ts
    openai-responses.ts
    openai-responses-lazy.ts
    openai-codex-responses.ts
    openai-codex-responses-lazy.ts
    azure-openai-responses.ts
    azure-openai-responses-lazy.ts
    anthropic-messages.ts
    anthropic-messages-lazy.ts
    google-generative-ai.ts
    google-generative-ai-lazy.ts
    google-vertex.ts
    google-vertex-lazy.ts
    mistral-conversations.ts
    mistral-conversations-lazy.ts
    bedrock-converse-stream.ts
    bedrock-converse-stream-lazy.ts
    lazy.ts                   # lazyStream()/lazyApi() helpers
    (shared helpers: openai-responses-shared, google-shared, transform-messages, ...)
  providers/                  # concrete provider factories and per-provider catalogs
    openai.ts
    openai.models.ts          # generated OpenAI catalog
    openai-codex.ts
    openai-codex.models.ts
    anthropic.ts
    anthropic.models.ts
    google.ts
    google.models.ts
    ...one pair per built-in provider...
    faux.ts                   # test provider factory
    all.ts                    # explicit aggregate: builtinModels(), getBuiltin*()
  utils/oauth/                # OAuth flow implementations (node), lazy-loaded

src/index.ts must stay core-only. It must not import:

• generated model catalogs
• built-in provider factories
• provider SDK implementations
• Node-only OAuth modules
• providers/all
• compat

Provider, API, and compat entrypoints are explicit subpath exports.

Public usage

Minimal provider usage:

import { createModels } from "@earendil-works/pi-ai";
import { openaiProvider } from "@earendil-works/pi-ai/providers/openai";

const models = createModels();
models.setProvider(openaiProvider());

const model = await models.getModel("openai", "gpt-4o-mini");
if (!model) throw new Error("model not found");

const response = await models.complete(model, context);

Multiple providers:

const models = createModels();
models.setProvider(openaiProvider());
models.setProvider(openrouterProvider());

All built-ins, explicitly heavy metadata entrypoint:

import { builtinModels } from "@earendil-works/pi-ai/providers/all";

const models = builtinModels({ oauth: "node" });

providers/all may import all provider metadata/catalogs. It still must not eagerly import SDK implementations; provider streams use lazy wrappers.

Core runtime: Models

Models is a provider collection plus auth application and stream convenience. No stream registry, no auth resolver strategy object.

export function createModels(options?: { credentials?: CredentialStore }): MutableModels;

export interface Models {
  getProviders(): readonly Provider[];
  getProvider(id: string): Provider | undefined;

  getModels(provider?: string, options?: { forceRefresh?: boolean }): Promise<readonly Model<Api>[]>;
  getModel(provider: string, id: string, options?: { forceRefresh?: boolean }): Promise<Model<Api> | undefined>;

  /** Resolve request auth for a model. Includes source label for status UI. */
  getAuth(model: Model<Api>): Promise<AuthResolution | undefined>;

  stream<TApi extends Api>(
    model: Model<TApi>,
    context: Context,
    options?: ApiStreamOptions<TApi>,
  ): AssistantMessageEventStream;

  complete<TApi extends Api>(
    model: Model<TApi>,
    context: Context,
    options?: ApiStreamOptions<TApi>,
  ): Promise<AssistantMessage>;

  streamSimple(model: Model<Api>, context: Context, options?: SimpleStreamOptions): AssistantMessageEventStream;
  completeSimple(model: Model<Api>, context: Context, options?: SimpleStreamOptions): Promise<AssistantMessage>;
}

export interface MutableModels extends Models {
  /** Upsert/replace by provider.id. Provider ids are unique. */
  setProvider(provider: Provider): void;
  deleteProvider(id: string): void;
  clearProviders(): void;
}

Removed concepts:

no Models.setStreamFunctions() / getStreamFunctions()
no api-registry as a real dispatch mechanism
no Models.provider(id) builder, no setModel/upsertModel/patchModel lifecycle
no ModelAuthResolver / setAuthResolver — resolution policy is fixed, store is injected

If an app needs different auth policy, it wraps providers (wrap auth methods or getModels) or passes explicit request auth in stream options.

Provider

A provider is the concrete runtime unit. It owns id/name/base metadata, auth methods, model listing, and stream behavior.

export interface Provider {
  readonly id: string;
  readonly name: string;

  readonly baseUrl?: string;
  readonly headers?: Record<string, string>;

  /** Required. Empty array for no-auth providers. */
  readonly auth: readonly AuthMethod[];

  getModels(options?: { forceRefresh?: boolean }): Promise<readonly Model<Api>[]>;

  stream<TApi extends Api>(
    model: Model<TApi>,
    context: Context,
    options?: ApiStreamOptions<TApi>,
  ): AssistantMessageEventStream;

  streamSimple(model: Model<Api>, context: Context, options?: SimpleStreamOptions): AssistantMessageEventStream;
}

There is no Provider.api field. model.api carries API identity; the provider dispatches internally (see createProvider()).

Model.api remains: existing metadata and tests use it, it is useful for diagnostics, and provider construction uses it for API implementation selection. But Models never dispatches on it; the provider does.

Typed stream options

Full stream options are API-specific. Model<TApi> pays off by deriving the option type from the API:

// types.ts — type-only imports from API impl modules are erased, so this is tree-shake safe
export interface ApiOptionsMap {
  "anthropic-messages": AnthropicOptions;
  "openai-completions": OpenAICompletionsOptions;
  "openai-responses": OpenAIResponsesOptions;
  "openai-codex-responses": OpenAICodexResponsesOptions;
  "azure-openai-responses": AzureOpenAIResponsesOptions;
  "google-generative-ai": GoogleOptions;
  "google-vertex": GoogleVertexOptions;
  "mistral-conversations": MistralOptions;
  "bedrock-converse-stream": BedrockOptions;
}

export type ApiStreamOptions<TApi extends Api> = TApi extends keyof ApiOptionsMap
  ? ApiOptionsMap[TApi]
  : StreamOptions & Record<string, unknown>;

Custom api strings fall back to the generic shape.

Name collision

types.ts currently exports type Provider = KnownProvider | string (a provider id). Rename that alias to ProviderId and fix call sites. The Provider interface above takes the name.

Provider model listing

Provider.getModels() is async and returns full Model<Api> objects. Static providers wrap their catalog; dynamic providers (llama.cpp, OpenRouter live listing) fetch and cache, honoring forceRefresh.

Dynamic model listing must be side-effect-free discovery:

OK: fetch /v1/models, enumerate local catalog, refresh cached remote model list
Not OK: load model, download model, mutate server state, run request probe

Provider-specific model lifecycle (load/unload) belongs in app/provider-management commands, not in getModels().

Streaming path

Models.stream() finds the provider by model.provider, resolves auth, merges it into request options, and delegates:

function stream(model, context, options) {
  const provider = this.getProvider(model.provider);
  if (!provider) {
    // produce an error stream, not a throw — see Error behavior
  }

  // async setup happens inside the returned stream (lazyStream pattern)
  const resolution = await this.getAuth(model);
  const requestModel = resolution?.auth.baseUrl ? { ...model, baseUrl: resolution.auth.baseUrl } : model;
  const requestOptions = mergeAuth(options, resolution?.auth); // explicit options win per-field

  return provider.stream(requestModel, context, requestOptions);
}

stream() returns AssistantMessageEventStream synchronously; async setup (auth resolution, lazy module load) happens inside the returned stream. The forwarding pattern already exists in today's register-builtins.ts (createLazyStream); extract it as lazyStream() in src/api/lazy.ts.

No request hot-path model canonicalization: stream() uses the supplied model object as-is. If an app wants fresh model metadata, it calls models.getModel(provider, id, { forceRefresh: true }) before starting the turn.

API implementations under src/api

An API implementation is reusable stream behavior. It is not a provider.

Uniform export contract — every real implementation module exports exactly:

// src/api/anthropic-messages.ts — imports SDKs
export function stream(model, context, options) { ... }
export function streamSimple(model, context, options) { ... }

This makes the module itself satisfy ProviderStreams, so the lazy wrapper is one generic helper instead of bespoke per-API plumbing:

export interface ProviderStreams {
  stream<TApi extends Api>(
    model: Model<TApi>,
    context: Context,
    options?: ApiStreamOptions<TApi>,
  ): AssistantMessageEventStream;
  streamSimple(model: Model<Api>, context: Context, options?: SimpleStreamOptions): AssistantMessageEventStream;
}

// src/api/lazy.ts
export function lazyApi(load: () => Promise<ProviderStreams>): ProviderStreams;

// src/api/anthropic-messages-lazy.ts
export const anthropicMessagesApi = (): ProviderStreams => lazyApi(() => import("./anthropic-messages.ts"));

Import chain:

provider module -> lazy API wrapper -> dynamic import(real API impl) -> SDK deps

Notes:

• Bedrock keeps the node-only dynamic import trick (importNodeOnlyProvider, .ts/.js specifier rewrite) inside its lazy wrapper. setBedrockProviderModule() (used by the Bun build) moves into the bedrock lazy wrapper module.
• Shared helper modules (openai-responses-shared.ts, google-shared.ts, transform-messages.ts, prompt-cache, copilot headers) move to src/api/ alongside the implementations.

Shared API implementations across concrete providers

Many concrete providers share an API implementation (OpenAI-completions: OpenRouter, Groq, Cerebras, xAI, ZAI, ...). They share lazy API objects by reference:

import { openAICompletionsApi } from "../api/openai-completions-lazy.ts";

export function openrouterProvider(): Provider {
  return createProvider({
    id: "openrouter",
    name: "OpenRouter",
    baseUrl: "https://openrouter.ai/api/v1",
    auth: [envApiKeyMethod({ id: "api-key", name: "OpenRouter API key", env: ["OPENROUTER_API_KEY"] })],
    models: OPENROUTER_MODELS,
    api: openAICompletionsApi(),
  });
}

This copies Vercel AI SDK's useful property: users import concrete providers; shared protocol implementation is internal.

Auth

Request auth output stays small:

export interface ModelAuth {
  apiKey?: string;
  headers?: Record<string, string>;
  baseUrl?: string;
}

If a value cannot be expressed as apiKey, headers, or baseUrl, it is provider config, not auth (Vertex project/location, Bedrock region/profile, Azure apiVersion are provider factory options).

Auth methods

Provider.auth is a list of uniform auth methods. The kind discriminant keeps the UI's oauth-vs-api-key split and types the credential:

export interface ApiKeyAuthMethod {
  kind: "api-key";
  id: string;   // unique within provider, e.g. "api-key"
  name: string; // "Anthropic API key"

  /** Interactive setup (prompt for key/metadata). Absent = ambient-only (env, ADC, IAM). */
  login?(callbacks: AuthLoginCallbacks): Promise<LocalCredential>;

  resolve(input: {
    model: Model<Api>;
    ctx: ProviderAuthContext;
    credential?: LocalCredential;
  }): Promise<AuthResolution | undefined>;
}

export interface OAuthAuthMethod {
  kind: "oauth";
  id: string;   // e.g. "oauth"
  name: string; // "Anthropic (Claude Pro/Max)"

  login(callbacks: AuthLoginCallbacks): Promise<OAuthCredential>;

  resolve(input: {
    model: Model<Api>;
    ctx: ProviderAuthContext;
    credential?: OAuthCredential;
  }): Promise<AuthResolution | undefined>;
}

export type AuthMethod = ApiKeyAuthMethod | OAuthAuthMethod;

export interface AuthResolution {
  auth: ModelAuth;
  /** Human-readable label for status UI: "ANTHROPIC_API_KEY", "OAuth", "~/.aws/credentials". */
  source?: string;
  /** Present when the method refreshed/updated the credential; Models persists it via the store. */
  credential?: Credential;
}

export interface ProviderAuthContext {
  env(name: string): Promise<string | undefined>;
  fileExists(path: string): Promise<boolean>; // supports leading ~
}

There is no usesCallbackServer flag. With prompt()/notify() callbacks the flow self-describes at runtime: a flow that runs a callback server issues a manual_code prompt racing the server and aborts the prompt when the callback wins. The UI needs no static foreknowledge.

Credentials

export interface LocalCredential {
  type: "local";
  key?: string;
  metadata?: Record<string, string>; // e.g. Cloudflare accountId/gatewayId
}

export interface OAuthCredential extends OAuthCredentials {
  type: "oauth";
}

export type Credential = LocalCredential | OAuthCredential;

LocalCredential.metadata exists for providers like Cloudflare that store non-key values (account id, gateway id) alongside or instead of a key. The method's resolve() merges per field: credential.key ?? env("CLOUDFLARE_API_TOKEN"), credential.metadata?.accountId ?? env("CLOUDFLARE_ACCOUNT_ID"), etc.

Credential store

The app injects storage; pi-ai ships an in-memory default.

export interface CredentialStore {
  get(providerId: string, methodId: string): Promise<Credential | undefined>;
  set(providerId: string, methodId: string, credential: Credential): Promise<void>;
  delete(providerId: string, methodId: string): Promise<void>;
}

coding-agent later implements this over AuthStorage. Login/logout orchestration is app-owned: the app calls method.login(callbacks) and persists the returned credential itself. Models only reads the store during resolution, and writes refreshed credentials when resolve() returns an updated one (OAuth token refresh).

Resolution policy (fixed)

Models.getAuth(model) resolves with a fixed policy. Precedence, highest first:

1. explicit request auth (stream options apiKey/headers) — merged per-field on top, in stream()
2. methods with a stored credential, in provider auth list order
3. methods resolving without a credential (ambient/env), in provider auth list order

Two-pass over provider.auth:

• Pass 1: for each method with a credential in the store, call resolve({ model, ctx, credential }); first non-undefined resolution wins.
• Pass 2: for each method, call resolve({ model, ctx }); first non-undefined resolution wins.

So an explicit login (stored credential) beats ambient env vars regardless of list order; list order breaks ties. Per-field merging within one method (stored key + env account id) happens inside that method's resolve().

If a resolution carries an updated credential, Models persists it via the store before returning.

Login callbacks

One interface serves api-key and OAuth login:

export interface AuthLoginCallbacks {
  signal?: AbortSignal;

  prompt(prompt: AuthPrompt, options?: { signal?: AbortSignal }): Promise<string>;
  notify(event: AuthEvent): void;
}

export type AuthPrompt =
  | { type: "text"; message: string; placeholder?: string }
  | { type: "secret"; message: string; placeholder?: string }
  | { type: "select"; message: string; options: readonly { id: string; label: string; description?: string }[] }
  | { type: "manual_code"; message: string; placeholder?: string };

export type AuthEvent =
  | { type: "auth_url"; url: string; instructions?: string }
  | { type: "device_code"; userCode: string; verificationUri: string; intervalSeconds?: number; expiresInSeconds?: number }
  | { type: "progress"; message: string };

prompt() returns the entered/selected string (select returns the option id). Flows race a manual_code prompt against a callback server by passing a per-prompt abort signal and aborting when the callback wins.

OAuth implementation target

OAuth must not force Node-only code (node:http, node:crypto) into browser bundles. Keep OAuth lazy; the provider factory decides which implementation to attach:

export type OAuthTarget = "node" | "web" | false;

export interface AnthropicProviderOptions {
  oauth?: OAuthTarget; // default false
}

export function anthropicProvider(options: AnthropicProviderOptions = {}): Provider {
  return createProvider({
    id: "anthropic",
    name: "Anthropic",
    baseUrl: "https://api.anthropic.com/v1",
    auth: [
      ...(options.oauth === "node"
        ? [lazyOAuthMethod({
            id: "oauth",
            name: "Anthropic (Claude Pro/Max)",
            load: () => import("../utils/oauth/anthropic.ts").then((m) => m.anthropicOAuthMethod),
          })]
        : []),
      envApiKeyMethod({ id: "api-key", name: "Anthropic API key", env: ["ANTHROPIC_API_KEY"] }),
    ],
    models: ANTHROPIC_MODELS,
    api: anthropicMessagesApi(),
  });
}

• Individual factories default to oauth: false.
• builtinModels({ oauth: "node" }) for pi CLI/coding-agent.
• "web" is reserved; web flows (sitegeist-style: Web Crypto PKCE, auth tab, extension tab APIs watching the localhost redirect, fetch token exchange, device-code polling for Copilot) are a follow-up. Until implemented, passing "web" throws at login time with a clear message.

lazyOAuthMethod() wraps a dynamically imported OAuthAuthMethod so provider definitions can advertise OAuth without importing the implementation:

export function lazyOAuthMethod(input: {
  id: string;
  name: string;
  load: () => Promise<OAuthAuthMethod>;
}): OAuthAuthMethod;

The existing flows in src/utils/oauth/ (anthropic, openai-codex, github-copilot) are adapted to OAuthAuthMethod with the new callbacks, staying Node-targeted and lazy-loaded.

Provider wrappers and models.json

models.json is a provider wrapper layer. It does not mutate providers in place:

function withProviderOverrides(base: Provider, overrides: ProviderOverrides): Provider {
  return {
    ...base,
    name: overrides.name ?? base.name,
    baseUrl: overrides.baseUrl ?? base.baseUrl,
    headers: mergeHeaders(base.headers, overrides.headers),

    async getModels(options) {
      const models = await base.getModels(options);
      return applyModelOverrides(models, overrides.models);
    },

    stream: base.stream,
    streamSimple: base.streamSimple,
  };
}

This composes with dynamic providers because getModels() delegates to the base source.

Request-auth config from models.json ($ENV, !command, inline keys) remains app-owned sidecar state, surfaced either as explicit request auth or as a custom ApiKeyAuthMethod the app prepends to the wrapped provider's auth list.

Custom providers: createProvider()

One helper builds providers from parts; it handles both single-API and mixed-API providers:

export function createProvider(input: {
  id: string;
  name?: string;                 // default: id
  baseUrl?: string;
  headers?: Record<string, string>;
  auth?: readonly AuthMethod[];  // default: []
  models:
    | readonly Model<Api>[]
    | ((options?: { forceRefresh?: boolean }) => Promise<readonly Model<Api>[]>);
  /** Single implementation, or map keyed by model.api for mixed-API providers. */
  api: ProviderStreams | Record<string, ProviderStreams>;
}): Provider;

• Single api: all models stream through it.
• Map api: stream()/streamSimple() dispatch on model.api; unknown api produces a stream error.

Mixed-API custom providers must be supported (opencode Go/Zen-style providers expose models backed by different APIs under one provider id).

Built-in provider factories use createProvider() internally. models.json custom providers map onto it directly:

{
  "providers": {
    "my-openai-proxy": {
      "api": "openai-completions",
      "baseUrl": "https://proxy.example/v1",
      "models": [ ... ]
    }
  }
}

Compat entrypoint

@earendil-works/pi-ai/compat preserves the old global API surface until the coding-agent migration deletes it. New code never imports it.

Old semantics being preserved: global stream() dispatched purely on model.api via the api-registry, with env API key injection. The compat module reproduces this:

• Lazily creates a default Models singleton from builtinModels({ oauth: "node" }) on first use.
• stream/complete/streamSimple/completeSimple(model, ctx, opts): look up getProvider(model.provider); if found, route through the singleton (auth resolution included). If not found (custom models.json/extension models), fall back to api-dispatch through a hidden createProvider() map containing all builtin API implementations plus anything registered via compat registerApiProvider().
• registerApiProvider()/unregisterApiProviders() feed that fallback dispatch map. api-registry.ts dies as a real mechanism.
• Sync getModel/getModels/getProviders become deprecated aliases of getBuiltinModel/getBuiltinModels/getBuiltinProviders (they were always pure generated-catalog reads — verified: nothing ever mutated the old modelRegistry).
• Re-exports setBedrockProviderModule from the bedrock lazy wrapper.
• getEnvApiKey/env-api-keys.ts stays available from compat only; provider auth methods own env lookup in the new design.

coding-agent switches imports of these symbols from @earendil-works/pi-ai to @earendil-works/pi-ai/compat (import-path-only change) and is otherwise untouched until the ModelManager migration.

Builtin static helpers

Typed, sync, generated-catalog-only helpers live with the catalogs (exported from providers/all):

getBuiltinModel(provider, id)   // sync, typed overloads from generated catalog
getBuiltinModels(provider)      // sync
getBuiltinProviders()           // sync

Runtime lookup is always the async instance API: await models.getModel(...).

Generated catalogs are split per provider (providers/<id>.models.ts) by updating packages/ai/scripts/generate-models.ts. If the generator change turns out too large for this pass, splitting may be deferred; providers/all and provider factories may temporarily import the monolithic models.generated.ts, relying on sideEffects: false for pruning.

Tree-shaking and lazy imports

Rules:

1. Main @earendil-works/pi-ai import is core-only.
2. Provider modules import their catalog, auth helpers, and lazy API wrappers only.
3. Lazy API wrappers dynamically import real API implementations.
4. Real API implementations import SDK dependencies.
5. OAuth implementations are selected by factory option (oauth: "node" | "web" | false) and lazy-loaded; provider metadata never eagerly imports Node-only OAuth code.
6. providers/all may import all provider metadata, but no eager SDK imports.
7. Provider modules are side-effect-free; importing a provider does not register anything globally.
8. package.json sets sideEffects: false.

Exports map sketch:

{
  "exports": {
    ".": "./dist/index.js",
    "./compat": "./dist/compat.js",
    "./providers/all": "./dist/providers/all.js",
    "./providers/openai": "./dist/providers/openai.js",
    "./providers/anthropic": "./dist/providers/anthropic.js",
    "./providers/*": "./dist/providers/*.js",
    "./api/*": "./dist/api/*.js"
  }
}

Browser smoke check (scripts/check-browser-smoke.mjs) must keep passing: bundling the core entrypoint (and any non-node provider entrypoint) must not pull node:http/node:crypto.

AgentHarness integration

AgentHarness receives a Models instance.

• AgentHarnessOptions.models is required.
• The harness does not snapshot Models into turn state.
• Request path calls this.models.streamSimple(model, context, options); same for compaction/branch-summarization paths.
• Request path never calls async models.getModel() to canonicalize; if model metadata needs refresh, the app updates the selected model before starting a turn.
• Harness tests build createModels() and install the faux provider (fauxProvider() factory from providers/faux).

coding-agent next phase (not this pass)

coding-agent builds providers in layers and binds them per session:

built-in providers (builtinModels)
-> models.json provider wrappers / custom providers (createProvider)
-> extension provider wrappers/additions

sessionModels.clearProviders();
for (const provider of layeredProviders) sessionModels.setProvider(provider);

coding-agent owns: AuthStorage-backed CredentialStore, models.json auth sidecar ($ENV, !command), command execution policy, provider status labels (from AuthResolution.source), login/logout UI (driving method.login() with prompt()/notify()), extension lifecycle, provider-management slash commands.

Until then, the only coding-agent changes in this pass are:

• construct a Models instance for AgentHarness (builtins + legacy api-dispatch fallback bridging ModelRegistry custom providers)
• switch old-global imports to @earendil-works/pi-ai/compat
• adapt the login dialog to prompt()/notify() callbacks (thin UI adapter; replaces the usesCallbackServer special-casing)

Implementation TODOs

Check items off as they land. Keep this list current; it is the working state for resumed sessions.

Phase 1 — core types/runtime

• Rename types.ts Provider alias to ProviderId; fix call sites.
• Add ApiOptionsMap and ApiStreamOptions<TApi> to types.ts (type-only imports).
• New models.ts: Provider interface, AuthMethod union (ApiKeyAuthMethod/OAuthAuthMethod), LocalCredential/OAuthCredential/Credential, CredentialStore (+ in-memory default), AuthResolution, ProviderAuthContext, ModelAuth, ModelsError + codes.
• Models/MutableModels/createModels({ credentials? }) with provider map, async getModel(s) (per-provider failure isolation), getAuth (two-pass fixed policy, persists refreshed credentials), stream/complete/streamSimple/completeSimple with per-field auth merge.
• Keep metadata helpers: calculateCost, getSupportedThinkingLevels, clampThinkingLevel, modelsAreEqual.

Phase 2 — src/api/

• Move stream implementations from src/providers/ to src/api/, renamed by API id (anthropic.ts -> api/anthropic-messages.ts, etc.).
• Normalize each implementation module to export exactly stream and streamSimple.
• Move shared helpers (openai-responses-shared, google-shared, transform-messages, openai-prompt-cache, github-copilot-headers) to src/api/.
• Extract lazyStream()/lazyApi() into src/api/lazy.ts.
• Add *-lazy.ts wrappers per API; bedrock keeps node-only import trick and setBedrockProviderModule().
• Delete providers/register-builtins.ts.

Phase 3 — provider factories + catalogs

• Auth helpers in src/auth/: envApiKeyMethod(), lazyOAuthMethod(), OAuthTarget, AuthLoginCallbacks/AuthPrompt/AuthEvent.
• createProvider() (single + mixed api map, dispatch on model.api).
• Per-provider factories under src/providers/ for all built-in catalog providers, oauth factory options where applicable.
• providers/all.ts: builtinModels({ oauth? }), getBuiltinModel/getBuiltinModels/getBuiltinProviders.
• Faux provider factory (providers/faux.ts) for tests.
• Split generated catalogs per provider via scripts/generate-models.ts (providers/<id>.models.ts) — or record explicitly that this is deferred.

Phase 4 — OAuth adaptation

• Adapt utils/oauth/anthropic.ts, openai-codex.ts, github-copilot.ts to OAuthAuthMethod + prompt()/notify().
• Remove usesCallbackServer; callback-server flows race a manual_code prompt instead.
• oauth: "web" reserved: throws at login with clear message.

Phase 5 — packaging

• index.ts core-only (no catalogs, no provider factories, no OAuth, no compat).
• compat.ts: default builtin singleton, stream/complete/streamSimple/completeSimple with api-dispatch fallback, registerApiProvider/unregisterApiProviders, deprecated getModel/getModels/getProviders aliases, setBedrockProviderModule re-export, getEnvApiKey.
• Subpath exports map; sideEffects: false.
• Browser smoke + shrinkwrap checks green.

Phase 6 — AgentHarness

• AgentHarnessOptions.models required; harness stream path uses models.streamSimple().
• Compaction/branch-summarization paths use the harness Models instance.
• Harness tests use createModels() + faux provider.

Phase 7 — coding-agent bridge (minimal)

• Construct Models for the harness (builtins + legacy api-dispatch fallback for ModelRegistry custom providers).
• Switch old-global imports to @earendil-works/pi-ai/compat.
• Login dialog adapter for prompt()/notify() callbacks.

Phase 8 — wrap-up

• Update/add tests; run affected suites (./test.sh or per-package vitest).
• packages/ai/CHANGELOG.md: ### Breaking Changes entry with a migration guide (old global stream/streamSimple/complete/completeSimple, getModel/getModels/getProviders, registerApiProvider, Provider -> ProviderId rename, OAuth callback changes; old API -> createModels()/provider factories or /compat as interim).
• packages/coding-agent/CHANGELOG.md: ### Breaking Changes entry with a migration guide for extension authors who work directly with pi-ai through coding-agent (e.g. custom providers via registerApiProvider, model access, login/auth hooks): what changed, what to import now, compat timeline.
• packages/agent/CHANGELOG.md: ### Breaking Changes entry for required AgentHarnessOptions.models.
• npm run check clean.

Deferred / follow-ups

• Web OAuth implementations (sitegeist-style) behind oauth: "web".
• coding-agent ModelRegistry -> session ModelManager migration; delete /compat.
• Images API registry redesign (untouched in this pass).

Error behavior

undefined means not found or not configured. Real failures reject or become stream errors.

export type ModelsErrorCode =
  | "model_source"      // provider getModels() failed
  | "model_validation"  // model object invalid
  | "provider"          // unknown provider, dispatch failure
  | "stream"            // stream setup failure
  | "auth"              // auth resolution failure
  | "oauth";            // oauth login/refresh failure

• Models.stream() produces stream errors (error event + error result) for async setup failures; it does not throw after returning the stream.
• Models.getModels() with no provider filter isolates per-provider source failures so one dynamic provider failure does not prevent listing others.