diff --git a/packages/agent/docs/models.md b/packages/agent/docs/models.md
new file mode 100644
index 000000000..0814068f7
--- /dev/null
+++ b/packages/agent/docs/models.md
@@ -0,0 +1,860 @@
+# Models architecture
+
+This document describes the target design for the next `pi-ai` model/provider refactor. It intentionally describes the desired shape, not the current implementation.
+
+Goals:
+
+- `Models` is a dumb runtime collection of providers.
+- Concrete providers own metadata, auth, model listing, and stream behavior.
+- API implementations live under `src/ai/` and are reusable/lazy.
+- Concrete provider factories live under `src/providers/`.
+- Users can import only the providers they need.
+- Importing a provider should 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.
+
+Non-goals for the immediate `pi-ai` pass:
+
+- Do not migrate coding-agent `ModelRegistry` yet.
+- Do not preserve old process-global APIs unless as explicit temporary compatibility shims.
+- Do not keep the stream/API registry inside `Models`.
+
+## Package layout
+
+Target source layout:
+
+```txt
+packages/ai/src/
+  index.ts                    # core exports only; no built-in provider imports
+  models.ts                   # Models, Provider, auth, runtime types
+  auth/                       # shared auth helpers, local/OAuth wrappers
+  ai/                         # API implementations and lazy API wrappers
+    openai-compatible.ts      # real implementation, imports SDKs
+    openai-compatible-lazy.ts # lightweight lazy wrapper
+    anthropic.ts
+    anthropic-lazy.ts
+    bedrock.ts
+    bedrock-lazy.ts
+    ...
+  providers/                  # concrete provider factories and per-provider catalogs
+    openai.ts
+    openai.models.ts          # OpenAI provider catalog
+    openai-codex.ts
+    openai-codex.models.ts    # OpenAI Codex provider catalog
+    openrouter.ts
+    openrouter.models.ts
+    anthropic.ts
+    anthropic.models.ts
+    google-vertex.ts
+    google-vertex.models.ts
+    bedrock.ts
+    bedrock.models.ts
+    cloudflare-ai-gateway.ts
+    cloudflare-ai-gateway.models.ts
+    all.ts                    # explicit aggregate for pi CLI/coding-agent
+```
+
+`src/index.ts` must stay core-only. It must not import:
+
+- all generated model metadata
+- built-in provider factories
+- provider SDK implementations
+- Node-only OAuth modules
+- `providers/all`
+
+Provider and API entrypoints are explicit subpath exports.
+
+## Public usage
+
+Minimal provider usage:
+
+```ts
+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:
+
+```ts
+import { createModels } from "@earendil-works/pi-ai";
+import { openaiProvider } from "@earendil-works/pi-ai/providers/openai";
+import { openrouterProvider } from "@earendil-works/pi-ai/providers/openrouter";
+
+const models = createModels();
+models.setProvider(openaiProvider());
+models.setProvider(openrouterProvider());
+```
+
+All built-ins, explicitly heavy metadata entrypoint:
+
+```ts
+import { builtinModels } from "@earendil-works/pi-ai/providers/all";
+
+const models = builtinModels();
+```
+
+`providers/all` may import all provider metadata/catalogs. It still must not eagerly import heavy SDK implementations; provider streams use lazy wrappers.
+
+## Core runtime: Models
+
+`Models` is a provider collection plus auth application and stream convenience. It does not contain a stream registry.
+
+```ts
+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>;
+
+  getAuth(model: Model<Api>): Promise<ModelAuth | 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<TApi extends Api>(
+    model: Model<TApi>,
+    context: Context,
+    options?: SimpleStreamOptions,
+  ): AssistantMessageEventStream;
+
+  completeSimple<TApi extends Api>(
+    model: Model<TApi>,
+    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;
+
+  getAuthResolver(): ModelAuthResolver;
+  setAuthResolver(resolver: ModelAuthResolver): void;
+}
+```
+
+No stream registry:
+
+```txt
+remove Models.setStreamFunctions()
+remove Models.getStreamFunctions()
+remove api-registry as real API
+```
+
+No provider builder mutation API as public API:
+
+```txt
+remove/avoid Models.provider(id)
+remove setModel/upsertModel/patchModel public lifecycle
+```
+
+A `MutableModels` implementation may still use internal maps, but the public object is provider-oriented.
+
+## Provider
+
+A provider is the concrete runtime unit. It owns:
+
+- id/name/base metadata
+- auth behavior
+- model listing
+- stream behavior
+
+Full stream options are API-specific. The generic `Model<TApi>` only pays off if the stream option type is derived from `TApi`.
+
+```ts
+export type ApiStreamOptions<TApi extends Api> = StreamOptionsForApi<TApi>;
+
+export interface Provider {
+  readonly id: string;
+  readonly name: string;
+
+  /** Default model API metadata/diagnostics, not Models dispatch. */
+  readonly api?: Api;
+
+  readonly baseUrl?: string;
+  readonly headers?: Record<string, string>;
+
+  /** Required. Use {} for no-auth providers. */
+  readonly auth: ProviderAuth;
+
+  getModels(options?: { forceRefresh?: boolean }): Promise<readonly Model<Api>[]>;
+
+  stream<TApi extends Api>(
+    model: Model<TApi>,
+    context: Context,
+    options?: ApiStreamOptions<TApi>,
+  ): AssistantMessageEventStream;
+
+  streamSimple<TApi extends Api>(
+    model: Model<TApi>,
+    context: Context,
+    options?: SimpleStreamOptions,
+  ): AssistantMessageEventStream;
+}
+```
+
+`Model.api` should remain for now because:
+
+- existing metadata and tests use it
+- it is useful for diagnostics
+- custom provider helpers may use it for API implementation selection
+
+But `Models` no longer dispatches through `model.api`. The provider does.
+
+## Provider model sources
+
+Provider model listing is async.
+
+```ts
+export type ProviderModelSource =
+  | readonly Model<Api>[]
+  | ((options?: { forceRefresh?: boolean }) => Promise<readonly Model<Api>[]>);
+```
+
+Provider helpers can accept `ProviderModel[]` and resolve provider defaults, but public `Provider.getModels()` returns full `Model<Api>` objects.
+
+Dynamic model sources must be side-effect-free discovery:
+
+```txt
+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 belongs in app/provider-management commands, not in `getModels()`.
+
+## Streaming path
+
+`Models.stream()` finds the provider by `model.provider`, resolves request auth, applies request-scoped auth, and delegates to the provider.
+
+```ts
+async function stream(model, context, options) {
+  const provider = getProvider(model.provider);
+  if (!provider) throw new ModelsError(...);
+
+  const auth = await getAuth(model);
+  const requestModel = auth?.baseUrl ? { ...model, baseUrl: auth.baseUrl } : model;
+  const requestOptions = mergeAuthIntoOptions(options, auth);
+
+  return provider.stream(requestModel, context, requestOptions);
+}
+```
+
+`stream()` still returns `AssistantMessageEventStream` synchronously. Async setup happens inside the returned stream, as today.
+
+No request hot-path model canonicalization. If an app wants fresh model metadata after refresh, it must call:
+
+```ts
+const model = await models.getModel(provider, id, { forceRefresh: true });
+```
+
+before starting the turn.
+
+## API implementations under `src/ai`
+
+An API implementation is reusable stream behavior. It is not a provider.
+
+Example real implementation:
+
+```ts
+// src/ai/openai-compatible.ts
+import OpenAI from "openai";
+
+export function streamOpenAICompatible(...) { ... }
+export function streamSimpleOpenAICompatible(...) { ... }
+```
+
+Example lazy wrapper:
+
+```ts
+// src/ai/openai-compatible-lazy.ts
+export function openAICompatibleApi(): ProviderStreams {
+  return {
+    stream(model, context, options) {
+      return lazyStream(() =>
+        import("./openai-compatible.ts").then((m) =>
+          m.streamOpenAICompatible(model, context, options),
+        ),
+      );
+    },
+
+    streamSimple(model, context, options) {
+      return lazyStream(() =>
+        import("./openai-compatible.ts").then((m) =>
+          m.streamSimpleOpenAICompatible(model, context, options),
+        ),
+      );
+    },
+  };
+}
+```
+
+Provider modules import lazy API wrappers, never real SDK-heavy implementation modules.
+
+```txt
+provider module -> lazy API wrapper -> dynamic import(real API impl) -> SDK deps
+```
+
+This preserves both:
+
+- provider-owned stream behavior
+- lazy SDK loading
+
+## Shared API implementations across concrete providers
+
+Many concrete providers share an API implementation. Example:
+
+- OpenAI
+- OpenRouter
+- Groq
+- Together
+- DeepSeek
+- Cloudflare AI Gateway OpenAI-compatible models
+
+They should share lazy API objects by reference, not through `Models` stream registry.
+
+```ts
+import { openAICompatibleApi } from "../ai/openai-compatible-lazy.ts";
+
+const api = openAICompatibleApi();
+
+export function openrouterProvider(): Provider {
+  return {
+    id: "openrouter",
+    name: "OpenRouter",
+    api: "openai-completions",
+    baseUrl: "https://openrouter.ai/api/v1",
+    auth: { local: envLocalAuth(["OPENROUTER_API_KEY"]) },
+    getModels: staticModels(OPENROUTER_MODELS),
+    stream: api.stream,
+    streamSimple: api.streamSimple,
+  };
+}
+```
+
+This copies Vercel AI SDK’s useful property: users import concrete providers, while shared protocol implementation is internal.
+
+## Auth
+
+Request auth output stays small.
+
+```ts
+export interface ModelAuth {
+  apiKey?: string;
+  headers?: Record<string, string>;
+  baseUrl?: string;
+}
+```
+
+No `streamOptions` in auth. If a value cannot be expressed as `apiKey`, `headers`, or `baseUrl`, it is provider config, not auth.
+
+Provider auth:
+
+```ts
+export interface ProviderAuth {
+  local?: LocalAuthProvider;
+  oauth?: OAuthProvider;
+}
+```
+
+`auth` is required on `Provider`; no-auth providers use `{}`.
+
+### Local auth
+
+Local auth covers non-OAuth credentials:
+
+- env API keys
+- files on disk
+- ambient SDK credentials
+- AuthStorage local credentials
+- models.json local credentials
+- provider-specific credential metadata
+
+```ts
+export interface ProviderAuthContext {
+  env(name: string): Promise<string | undefined>;
+  fileExists(path: string): Promise<boolean>; // supports leading ~
+}
+
+export interface LocalCredential {
+  type: "local";
+  key?: string;
+  metadata?: Record<string, string>;
+}
+
+export interface OAuthCredential extends OAuthCredentials {
+  type: "oauth";
+}
+
+export type Credential = LocalCredential | OAuthCredential;
+
+export interface LocalAuthProvider {
+  id: string;
+  name: string;
+
+  login?(callbacks: AuthLoginCallbacks): Promise<LocalCredential>;
+
+  resolve(input: {
+    model: Model<Api>;
+    ctx: ProviderAuthContext;
+    credential?: LocalCredential;
+  }): Promise<AuthResolution | undefined>;
+}
+
+export interface AuthResolution {
+  auth: ModelAuth;
+  sources: readonly ProviderAuthSource[];
+}
+
+export type ProviderAuthSource =
+  | { type: "env"; name: string }
+  | { type: "file"; path: string; label?: string }
+  | { type: "ambient"; label: string };
+```
+
+Local auth receives an optional credential from the app. It does not read AuthStorage itself.
+
+Examples:
+
+- OpenAI: `credential.key ?? env("OPENAI_API_KEY")` -> `{ apiKey }`
+- Bedrock: bearer token -> `{ apiKey }`; AWS profile/IAM/ECS/IRSA -> `{}`
+- Vertex: API key -> `{ apiKey }`; ADC files -> `{}`
+- Cloudflare: key + account/gateway metadata/env -> `{ apiKey, baseUrl }`
+
+### OAuth
+
+```ts
+export interface OAuthProvider {
+  id: string;
+  name: string;
+  usesCallbackServer?: boolean;
+
+  login(callbacks: AuthLoginCallbacks): Promise<OAuthCredential>;
+
+  resolve(credentials: OAuthCredential): Promise<{
+    credentials: OAuthCredential;
+    auth: ModelAuth;
+  }>;
+}
+```
+
+OAuth receives stored OAuth credentials, may refresh them, and returns updated credentials for the app to persist.
+
+### Login callbacks
+
+One callback interface serves local and OAuth login. Use the nicer `prompt()` / `notify()` shape now instead of carrying forward the ad hoc OAuth callback bag.
+
+```ts
+export interface AuthLoginCallbacks {
+  signal?: AbortSignal;
+
+  prompt<TPrompt extends AuthPrompt>(
+    prompt: TPrompt,
+    options?: { signal?: AbortSignal },
+  ): Promise<AuthPromptResult<TPrompt>>;
+
+  notify(event: AuthEvent): void;
+}
+
+export type AuthPrompt =
+  | {
+      type: "text";
+      id: string;
+      message: string;
+      placeholder?: string;
+      allowEmpty?: boolean;
+      required?: boolean;
+    }
+  | {
+      type: "secret";
+      id: string;
+      message: string;
+      placeholder?: string;
+      required?: boolean;
+    }
+  | {
+      type: "select";
+      id: string;
+      message: string;
+      options: readonly { id: string; label: string; description?: string }[];
+    }
+  | {
+      type: "manual_code";
+      id: string;
+      message: string;
+      placeholder?: string;
+    };
+
+export type AuthPromptResult<TPrompt extends AuthPrompt> = 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 };
+```
+
+Codex browser login can race a `manual_code` prompt against a callback server by passing an abort signal to `prompt(..., { signal })` and aborting the prompt when the callback wins.
+
+### OAuth implementation target
+
+OAuth providers must not force Node-only code into browser bundles. Keep OAuth lazy, and let each concrete provider factory decide whether to attach a Node OAuth implementation, a web OAuth implementation, or no OAuth implementation.
+
+Do not build a universal OAuth runtime abstraction in this refactor. The provider factory option is enough:
+
+```ts
+export type OAuthTarget = "node" | "web" | false;
+
+export interface AnthropicProviderOptions {
+  oauth?: OAuthTarget;
+}
+
+export function anthropicProvider(options: AnthropicProviderOptions = {}): Provider {
+  return {
+    id: "anthropic",
+    name: "Anthropic",
+    api: "anthropic",
+    baseUrl: "https://api.anthropic.com/v1",
+    auth: {
+      local: envLocalAuth("anthropic-api-key", "Anthropic API key", ["ANTHROPIC_API_KEY"]),
+      oauth:
+        options.oauth === "node"
+          ? lazyOAuthProvider({
+              id: "anthropic",
+              name: "Anthropic (Claude Pro/Max)",
+              usesCallbackServer: true,
+              load: () => import("../oauth/anthropic-node.ts").then((m) => m.anthropicOAuthProvider),
+            })
+          : options.oauth === "web"
+            ? lazyOAuthProvider({
+                id: "anthropic",
+                name: "Anthropic (Claude Pro/Max)",
+                load: () => import("../oauth/anthropic-web.ts").then((m) => m.anthropicOAuthProvider),
+              })
+            : undefined,
+    },
+    getModels: staticModels(ANTHROPIC_MODELS),
+    stream: anthropicApi().stream,
+    streamSimple: anthropicApi().streamSimple,
+  };
+}
+```
+
+Recommended defaults:
+
+- individual provider factories default to `oauth: false` unless we intentionally want Node defaults
+- `providers/all` for pi CLI/coding-agent calls providers with `oauth: "node"`
+- browser users call providers with `oauth: "web"`
+- users that only want API-key/env auth leave OAuth disabled
+
+Sitegeist demonstrates that browser-compatible OAuth is practical for Anthropic, OpenAI Codex, GitHub Copilot, and Gemini CLI. The browser implementations use Web Crypto, auth tabs, localhost redirect URL watching through extension tab APIs, `fetch` for token exchange, CORS permissions/proxies where needed, and device-code polling for Copilot.
+
+So the target is not “OAuth is Node-only”. The target is: provider factories attach the right lazy OAuth module for the runtime the caller asked for.
+
+Use a lazy wrapper so provider definitions can advertise OAuth without importing the actual implementation:
+
+```ts
+export function lazyOAuthProvider(input: {
+  id: string;
+  name: string;
+  usesCallbackServer?: boolean;
+  load: () => Promise<OAuthProvider>;
+}): OAuthProvider {
+  return {
+    id: input.id,
+    name: input.name,
+    usesCallbackServer: input.usesCallbackServer,
+    async login(callbacks) {
+      return (await input.load()).login(callbacks);
+    },
+    async resolve(credentials) {
+      return (await input.load()).resolve(credentials);
+    },
+  };
+}
+```
+
+## Auth resolution policy
+
+`pi-ai` can ship a default resolver using injected context/store. Applications can replace it.
+
+Recommended default order, low to high precedence:
+
+```txt
+provider local auth defaults
+-> CredentialStore local/OAuth credential
+-> explicit request auth
+```
+
+coding-agent later adds models.json and CLI policy:
+
+```txt
+provider local auth defaults
+-> AuthStorage credential
+-> models.json auth sidecar
+-> CLI/runtime explicit request auth
+```
+
+Auth values merge:
+
+- later `apiKey` wins
+- later `baseUrl` wins
+- headers shallow-merge; later wins per header
+
+Cloudflare requires merge, not early return. It may need env account/gateway + stored key, or stored metadata + env token.
+
+## Provider wrappers and models.json
+
+`models.json` is naturally a provider wrapper layer.
+
+It should not mutate a provider in place. It should wrap:
+
+```ts
+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 provider source.
+
+Request-auth config from models.json remains app-owned sidecar state. It is not stored in `Provider` unless it is true provider metadata such as base URL or headers.
+
+## Custom providers from models.json
+
+A models.json custom provider must become a concrete `Provider` object.
+
+### Single API custom provider
+
+If all models use one known API:
+
+```json
+{
+  "providers": {
+    "my-openai-proxy": {
+      "api": "openai-completions",
+      "baseUrl": "https://proxy.example/v1",
+      "models": [ ... ]
+    }
+  }
+}
+```
+
+coding-agent/pi-ai helper can build:
+
+```ts
+createApiBackedProvider({
+  id: "my-openai-proxy",
+  name: "my-openai-proxy",
+  api: "openai-completions",
+  baseUrl: "https://proxy.example/v1",
+  auth: {},
+  models,
+  apiImplementation: openAICompatibleApi(),
+});
+```
+
+This helper lives outside `Models`; it is provider construction sugar.
+
+### Mixed API custom provider
+
+Custom providers with mixed APIs must be supported. Existing providers such as opencode-go/zen can expose models backed by different APIs under one provider id. In this design that means the provider dispatches internally.
+
+```ts
+createDispatchProvider({
+  id,
+  models,
+  apis: {
+    "openai-completions": openAICompatibleApi(),
+    "anthropic": anthropicApi(),
+  },
+});
+```
+
+The returned provider still exposes only:
+
+```ts
+stream(model, context, options)
+streamSimple(model, context, options)
+```
+
+Internally it switches on `model.api` and calls the right lazy API implementation.
+
+This preserves the rule that `Models` has no stream registry while supporting required mixed-API providers.
+
+## Tree-shaking and lazy imports
+
+Rules:
+
+1. Main `@earendil-works/pi-ai` import is core-only.
+2. Provider modules import metadata, model 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 providers are selected by provider factory option (`oauth: "node" | "web" | false`) and lazy-loaded; provider metadata must not eagerly import Node-only OAuth code.
+6. `providers/all` is explicit and allowed to import all provider metadata, but still no eager SDK imports.
+7. Provider modules are side-effect-free; importing a provider does not register it globally.
+8. `package.json` should set `sideEffects: false` if all entrypoints are side-effect-free.
+
+Example exports:
+
+```json
+{
+  "exports": {
+    ".": "./dist/index.js",
+    "./providers/openai": "./dist/providers/openai.js",
+    "./providers/anthropic": "./dist/providers/anthropic.js",
+    "./providers/openrouter": "./dist/providers/openrouter.js",
+    "./providers/all": "./dist/providers/all.js",
+    "./ai/openai-compatible": "./dist/ai/openai-compatible-lazy.js"
+  }
+}
+```
+
+To avoid metadata bloat for minimal users, generated model catalogs should be split per provider. Until then, any provider module importing the monolithic generated catalog can pull more metadata than necessary.
+
+## Static typed helpers
+
+The old global sync helpers are incompatible with dynamic providers:
+
+```ts
+getModel(...)
+getModels(...)
+getProviders(...)
+```
+
+If they mean runtime lookup, they must be async. If they remain sync and read only built-ins, they are misleading.
+
+Target:
+
+- remove old global runtime helpers, or make them async and default-instance backed only in a compatibility entrypoint
+- add explicit static catalog helpers if type-safe built-in lookup is still desired
+
+```ts
+getBuiltinModel(provider, id)      // sync, generated catalog only
+getBuiltinModels(provider)        // sync, generated catalog only
+getBuiltinProviders()             // sync, generated catalog only
+```
+
+Runtime lookup is always:
+
+```ts
+await models.getModel(provider, id)
+await models.getModels(provider)
+```
+
+## AgentHarness integration
+
+`AgentHarness` receives a `Models` instance.
+
+Rules:
+
+- `AgentHarnessOptions.models` is required
+- harness does not snapshot `Models` into turn state
+- request path calls `models.streamSimple(model, context, options)` or equivalent
+- request path does not call async `models.getModel()` to canonicalize
+- if model metadata needs refresh, app updates the selected model before starting a turn
+
+## coding-agent next phase
+
+coding-agent should build providers in layers:
+
+```txt
+built-in providers
+-> models.json provider wrappers
+-> extension provider wrappers/additions
+```
+
+Then:
+
+```ts
+sessionModels.clearProviders();
+for (const provider of layeredProviders) sessionModels.setProvider(provider);
+sessionModels.setAuthResolver(codingAgentResolver);
+```
+
+coding-agent owns:
+
+- AuthStorage local/OAuth files
+- models.json auth sidecar
+- `$ENV` and `!command`
+- command execution policy
+- provider status labels
+- login/logout UI
+- extension lifecycle
+- provider-management slash commands
+
+## Migration TODOs
+
+1. Restore/remove half-implemented old auth/stream-registry changes before starting this design.
+2. Redesign `packages/ai/src/models.ts` around provider-owned streams.
+3. Remove `StreamFunctions` registry from `Models` public API.
+4. Introduce `Provider` with required `auth`, async `getModels()`, `stream()`, and `streamSimple()`.
+5. Add lazy API wrappers under `packages/ai/src/ai/`.
+6. Move real API implementations under `packages/ai/src/ai/` or adapt existing stream files into that layout.
+7. Add concrete provider factories under `packages/ai/src/providers/`.
+8. Add `providers/all` explicit aggregate.
+9. Add `lazyOAuthProvider()`, `OAuthTarget`, and provider factory options such as `anthropicProvider({ oauth: "node" | "web" | false })`.
+10. Convert built-in OAuth attachment to lazy target-specific wrappers.
+11. Split generated model catalogs per provider, or mark as follow-up if too large.
+12. Replace old global `defaultModels()`/global helpers with explicit instance usage or compatibility entrypoint.
+13. Add custom provider helpers:
+    - `createApiBackedProvider()`
+    - `createDispatchProvider()` for required mixed-API providers
+14. Update `AgentHarness` to use provider-owned `models.streamSimple()` without stream registry lookups.
+15. Keep coding-agent compatibility only as needed until the coding-agent `ModelManager` migration.
+16. Update tests to construct explicit `Models` instances and install only needed providers/faux providers.
+
+## Error behavior
+
+`undefined` means not found or not configured.
+Real failures reject or become stream errors.
+
+Recommended error codes:
+
+```ts
+export type ModelsErrorCode =
+  | "model_source"
+  | "model_validation"
+  | "provider"
+  | "stream"
+  | "auth"
+  | "oauth";
+```
+
+`Models.stream()` should produce stream errors for async setup failures. `getModels()` should isolate provider source failures when listing all providers if possible, so one dynamic provider failure does not prevent listing other providers.