feat(ai): move API implementations to src/api with lazy wrappers (phase 2)

Stream implementations move from src/providers/ to src/api/, renamed by
API id (anthropic.ts -> anthropic-messages.ts, google.ts ->
google-generative-ai.ts, mistral.ts -> mistral-conversations.ts,
amazon-bedrock.ts -> bedrock-converse-stream.ts). Every module now
exports exactly stream/streamSimple; shared helpers move alongside.

New ProviderStreams dispatch contract in types.ts, lazyApi() wrapper in
api/lazy.ts, and one .lazy.ts wrapper per API. Bedrock's wrapper keeps
the node-only variable-specifier import and setBedrockProviderModule()
(now taking ProviderStreams).

providers/register-builtins.ts deleted; interim until the compat
entrypoint lands, builtin api-registry registration lives in stream.ts
and lazy wrappers are exported from the root barrel. Old per-API lazy
exports (streamAnthropic, ...) are gone; package.json subpaths retarget
to dist/api/.

packages/ai/test/anthropic-eager-tool-input-compat.test.ts

@@ -2,7 +2,7 @@ import { createServer, type IncomingMessage, type ServerResponse } from "node:ht
 import type { AddressInfo } from "node:net";
 import { Type } from "typebox";
 import { describe, expect, it } from "vitest";
-import { streamAnthropic } from "../src/providers/anthropic.ts";
+import { stream as streamAnthropic } from "../src/api/anthropic-messages.ts";
 import type { Context, Model, Tool } from "../src/types.ts";
 
 interface CapturedRequest {

packages/ai/test/anthropic-sse-parsing.test.ts

@@ -1,8 +1,8 @@
 import type Anthropic from "@anthropic-ai/sdk";
 import { Type } from "typebox";
 import { describe, expect, it } from "vitest";
+import { stream as streamAnthropic } from "../src/api/anthropic-messages.ts";
 import { getModel } from "../src/models.ts";
-import { streamAnthropic } from "../src/providers/anthropic.ts";
 import type { Context, ToolCall } from "../src/types.ts";
 
 function createSseResponse(events: Array<{ event: string; data: string }>): Response {

packages/ai/test/azure-openai-base-url.test.ts

@@ -1,6 +1,6 @@
 import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+import { stream as streamAzureOpenAIResponses } from "../src/api/azure-openai-responses.ts";
 import { getModel } from "../src/models.ts";
-import { streamAzureOpenAIResponses } from "../src/providers/azure-openai-responses.ts";
 import type { Context } from "../src/types.ts";
 
 interface CapturedAzureClientOptions {

packages/ai/test/bedrock-convert-messages.test.ts

@@ -44,8 +44,8 @@ vi.mock("@aws-sdk/client-bedrock-runtime", () => {
 	};
 });
 
+import { stream as streamBedrock } from "../src/api/bedrock-converse-stream.ts";
 import { getModel } from "../src/models.ts";
-import { streamBedrock } from "../src/providers/amazon-bedrock.ts";
 import type { Context, Message } from "../src/types.ts";
 
 const baseModel = getModel("amazon-bedrock", "us.anthropic.claude-sonnet-4-5-20250929-v1:0");

packages/ai/test/bedrock-custom-headers.test.ts

@@ -51,9 +51,9 @@ vi.mock("@aws-sdk/client-bedrock-runtime", () => {
 	};
 });
 
+import type { BedrockOptions } from "../src/api/bedrock-converse-stream.ts";
+import { stream as streamBedrock, streamSimple as streamSimpleBedrock } from "../src/api/bedrock-converse-stream.ts";
 import { getModel } from "../src/models.ts";
-import type { BedrockOptions } from "../src/providers/amazon-bedrock.ts";
-import { streamBedrock, streamSimpleBedrock } from "../src/providers/amazon-bedrock.ts";
 import type { Context, Model } from "../src/types.ts";
 
 const context: Context = {

packages/ai/test/bedrock-endpoint-resolution.test.ts

@@ -44,8 +44,8 @@ vi.mock("@aws-sdk/client-bedrock-runtime", () => {
 	};
 });
 
+import { stream as streamBedrock } from "../src/api/bedrock-converse-stream.ts";
 import { getModel } from "../src/models.ts";
-import { streamBedrock } from "../src/providers/amazon-bedrock.ts";
 import type { Context, Model } from "../src/types.ts";
 
 const context: Context = {

packages/ai/test/bedrock-thinking-payload.test.ts

@@ -1,6 +1,6 @@
 import { describe, expect, it } from "vitest";
+import { type BedrockOptions, stream as streamBedrock } from "../src/api/bedrock-converse-stream.ts";
 import { getModel } from "../src/models.ts";
-import { type BedrockOptions, streamBedrock } from "../src/providers/amazon-bedrock.ts";
 import type { Context, Model } from "../src/types.ts";
 import { hasBedrockCredentials } from "./bedrock-utils.ts";
 

packages/ai/test/cache-retention.test.ts

@@ -1,8 +1,8 @@
 import { afterEach, beforeEach, describe, expect, it } from "vitest";
+import { stream as streamAnthropic } from "../src/api/anthropic-messages.ts";
+import { stream as streamOpenAICompletions } from "../src/api/openai-completions.ts";
+import { stream as streamOpenAIResponses } from "../src/api/openai-responses.ts";
 import { getModel } from "../src/models.ts";
-import { streamAnthropic } from "../src/providers/anthropic.ts";
-import { streamOpenAICompletions } from "../src/providers/openai-completions.ts";
-import { streamOpenAIResponses } from "../src/providers/openai-responses.ts";
 import { stream } from "../src/stream.ts";
 import type { Context, Model } from "../src/types.ts";
 

packages/ai/test/codex-websocket-cached-probe.ts

@@ -10,13 +10,13 @@ import { tmpdir } from "node:os";
 import { join, resolve } from "node:path";
 import { Type } from "typebox";
 import { AuthStorage } from "../../coding-agent/src/core/auth-storage.ts";
-import { getModel } from "../src/models.ts";
 import {
 	closeOpenAICodexWebSocketSessions,
 	getOpenAICodexWebSocketDebugStats,
 	resetOpenAICodexWebSocketDebugStats,
-	streamOpenAICodexResponses,
-} from "../src/providers/openai-codex-responses.ts";
+	stream as streamOpenAICodexResponses,
+} from "../src/api/openai-codex-responses.ts";
+import { getModel } from "../src/models.ts";
 import type { AssistantMessage, Context, Message, Model, Tool, ToolResultMessage, Transport } from "../src/types.ts";
 
 type ThinkingLevel = "minimal" | "low" | "medium" | "high" | "xhigh";

packages/ai/test/fireworks-models.test.ts

@@ -2,9 +2,9 @@ import { createServer, type IncomingMessage, type ServerResponse } from "node:ht
 import type { AddressInfo } from "node:net";
 import { Type } from "typebox";
 import { afterEach, describe, expect, it } from "vitest";
+import { stream as streamAnthropic } from "../src/api/anthropic-messages.ts";
 import { findEnvKeys, getEnvApiKey } from "../src/env-api-keys.ts";
 import { getModel, getModels } from "../src/models.ts";
-import { streamAnthropic } from "../src/providers/anthropic.ts";
 import type { Context, Model, Tool } from "../src/types.ts";
 
 const originalFireworksApiKey = process.env.FIREWORKS_API_KEY;

packages/ai/test/github-copilot-anthropic.test.ts

@@ -1,6 +1,6 @@
 import { describe, expect, it, vi } from "vitest";
+import { stream as streamAnthropic } from "../src/api/anthropic-messages.ts";
 import { getModel } from "../src/models.ts";
-import { streamAnthropic } from "../src/providers/anthropic.ts";
 import type { Context } from "../src/types.ts";
 
 const mockState = vi.hoisted(() => ({

packages/ai/test/google-shared-convert-tools.test.ts

@@ -1,5 +1,5 @@
 import { describe, expect, it } from "vitest";
-import { convertTools } from "../src/providers/google-shared.ts";
+import { convertTools } from "../src/api/google-shared.ts";
 import type { Tool } from "../src/types.ts";
 
 function makeTool(parameters: Record<string, unknown>): Tool {

packages/ai/test/google-shared-gemini3-unsigned-tool-call.test.ts

@@ -1,5 +1,5 @@
 import { describe, expect, it } from "vitest";
-import { convertMessages } from "../src/providers/google-shared.ts";
+import { convertMessages } from "../src/api/google-shared.ts";
 import type { Context, Model } from "../src/types.ts";
 
 function makeGemini3Model<TApi extends "google-generative-ai" | "google-vertex">(

packages/ai/test/google-shared-image-tool-result-routing.test.ts

@@ -1,5 +1,5 @@
 import { describe, expect, it } from "vitest";
-import { convertMessages } from "../src/providers/google-shared.ts";
+import { convertMessages } from "../src/api/google-shared.ts";
 import type { Context, Model } from "../src/types.ts";
 
 function makeModel<TApi extends "google-generative-ai">(

packages/ai/test/google-thinking-signature.test.ts

@@ -1,5 +1,5 @@
 import { describe, expect, it } from "vitest";
-import { isThinkingPart, retainThoughtSignature } from "../src/providers/google-shared.ts";
+import { isThinkingPart, retainThoughtSignature } from "../src/api/google-shared.ts";
 
 describe("Google thinking detection (thoughtSignature)", () => {
 	it("treats part.thought === true as thinking", () => {

packages/ai/test/google-vertex-api-key-resolution.test.ts

@@ -45,8 +45,8 @@ vi.mock("@google/genai", () => {
 	};
 });
 
+import { stream as streamGoogleVertex } from "../src/api/google-vertex.ts";
 import { getModel } from "../src/models.ts";
-import { streamGoogleVertex } from "../src/providers/google-vertex.ts";
 import type { Context, Model } from "../src/types.ts";
 
 const model = getModel("google-vertex", "gemini-3-flash-preview");

packages/ai/test/lazy-module-load.test.ts

@@ -66,7 +66,7 @@ describe("lazy provider module loading", () => {
 		expect(result.loadedSpecifiers).toEqual([]);
 	});
 
-	it("loads only the Anthropic SDK when calling the root lazy wrapper", () => {
+	it("loads only the Anthropic SDK when streaming through the lazy API wrapper", () => {
 		const result = runProbe(`
 			const model = {
 				id: "claude-sonnet-4-6",
@@ -81,7 +81,7 @@ describe("lazy provider module loading", () => {
 				maxTokens: 8192,
 			};
 			const context = { messages: [{ role: "user", content: "hi" }] };
-			await mod.streamSimpleAnthropic(model, context).result();
+			await mod.anthropicMessagesApi().streamSimple(model, context).result();
 		`);
 
 		expect(result.loadedSpecifiers).toEqual(["@anthropic-ai/sdk"]);

packages/ai/test/openai-codex-stream.test.ts

@@ -5,9 +5,9 @@ import { afterEach, describe, expect, it, vi } from "vitest";
 import {
 	getOpenAICodexWebSocketDebugStats,
 	resetOpenAICodexWebSocketDebugStats,
-	streamOpenAICodexResponses,
-	streamSimpleOpenAICodexResponses,
-} from "../src/providers/openai-codex-responses.ts";
+	stream as streamOpenAICodexResponses,
+	streamSimple as streamSimpleOpenAICodexResponses,
+} from "../src/api/openai-codex-responses.ts";
 import type { Context, Model } from "../src/types.ts";
 
 const originalAgentDir = process.env.PI_CODING_AGENT_DIR;

packages/ai/test/openai-completions-cache-control-format.test.ts

@@ -1,7 +1,7 @@
 import { Type } from "typebox";
 import { beforeEach, describe, expect, it, vi } from "vitest";
+import { stream as streamOpenAICompletions } from "../src/api/openai-completions.ts";
 import { getModel } from "../src/models.ts";
-import { streamOpenAICompletions } from "../src/providers/openai-completions.ts";
 import type { Model } from "../src/types.ts";
 
 interface CacheControl {

packages/ai/test/openai-completions-prompt-cache.test.ts

@@ -1,6 +1,6 @@
 import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+import { stream as streamOpenAICompletions } from "../src/api/openai-completions.ts";
 import { getModel } from "../src/models.ts";
-import { streamOpenAICompletions } from "../src/providers/openai-completions.ts";
 import type { Model } from "../src/types.ts";
 
 interface FakeOpenAIClientOptions {

packages/ai/test/openai-completions-retry.test.ts

@@ -1,5 +1,5 @@
 import { beforeEach, describe, expect, it, vi } from "vitest";
-import { streamOpenAICompletions } from "../src/providers/openai-completions.ts";
+import { stream as streamOpenAICompletions } from "../src/api/openai-completions.ts";
 import type { Context, Model } from "../src/types.ts";
 
 const mockState = vi.hoisted(() => ({

packages/ai/test/openai-completions-thinking-as-text.test.ts

@@ -2,7 +2,7 @@ import { once } from "node:events";
 import http from "node:http";
 import type { AddressInfo } from "node:net";
 import { afterEach, describe, expect, it } from "vitest";
-import { convertMessages, streamOpenAICompletions } from "../src/providers/openai-completions.ts";
+import { convertMessages, stream as streamOpenAICompletions } from "../src/api/openai-completions.ts";
 import type {
 	AssistantMessage,
 	AssistantMessageEvent,

packages/ai/test/openai-completions-tool-result-images.test.ts

@@ -1,6 +1,6 @@
 import { describe, expect, it } from "vitest";
+import { convertMessages } from "../src/api/openai-completions.ts";
 import { getModel } from "../src/models.ts";
-import { convertMessages } from "../src/providers/openai-completions.ts";
 import type {
 	AssistantMessage,
 	Context,

packages/ai/test/openai-responses-copilot-provider.test.ts

@@ -1,6 +1,6 @@
 import { afterEach, describe, expect, it, vi } from "vitest";
+import { stream as streamOpenAIResponses } from "../src/api/openai-responses.ts";
 import { getModel } from "../src/models.ts";
-import { streamOpenAIResponses } from "../src/providers/openai-responses.ts";
 import type { Model } from "../src/types.ts";
 
 type CapturedHeaders = Headers | string[][] | Record<string, string | readonly string[]> | undefined;

packages/ai/test/openai-responses-foreign-toolcall-id.test.ts

@@ -1,6 +1,6 @@
 import { describe, expect, it } from "vitest";
+import { convertResponsesMessages } from "../src/api/openai-responses-shared.ts";
 import { getModel } from "../src/models.ts";
-import { convertResponsesMessages } from "../src/providers/openai-responses-shared.ts";
 import type { AssistantMessage, Context, ToolResultMessage, Usage } from "../src/types.ts";
 import { shortHash } from "../src/utils/hash.ts";
 

packages/ai/test/openai-responses-message-id.test.ts

@@ -1,7 +1,7 @@
 import type { ResponseOutputMessage } from "openai/resources/responses/responses.js";
 import { describe, expect, it } from "vitest";
+import { convertResponsesMessages } from "../src/api/openai-responses-shared.ts";
 import { getModel } from "../src/models.ts";
-import { convertResponsesMessages } from "../src/providers/openai-responses-shared.ts";
 import type { AssistantMessage, Context, Usage } from "../src/types.ts";
 
 const usage: Usage = {

packages/ai/test/openai-responses-partial-json-cleanup.test.ts

@@ -1,6 +1,6 @@
 import type { ResponseStreamEvent } from "openai/resources/responses/responses.js";
 import { describe, expect, it, vi } from "vitest";
-import { processResponsesStream } from "../src/providers/openai-responses-shared.ts";
+import { processResponsesStream } from "../src/api/openai-responses-shared.ts";
 import type { AssistantMessage, AssistantMessageEvent, Model } from "../src/types.ts";
 import { AssistantMessageEventStream } from "../src/utils/event-stream.ts";
 

packages/ai/test/scratch.ts

@@ -2,10 +2,12 @@
 // Run from packages/ai: node test/scratch.ts
 // Requires ANTHROPIC_API_KEY.
 
+import { anthropicMessagesApi } from "../src/api/anthropic-messages.lazy.ts";
 import { createModels, getModels, type Provider } from "../src/models.ts";
-import { streamAnthropic, streamSimpleAnthropic } from "../src/providers/register-builtins.ts";
 import type { Context } from "../src/types.ts";
 
+const anthropicApi = anthropicMessagesApi();
+
 // ---------------------------------------------------------------------------
 // 1. Define a provider. In the final design this comes from
 //    `@earendil-works/pi-ai/providers/anthropic` as `anthropicProvider()`;
@@ -33,8 +35,8 @@ const anthropic: Provider<"anthropic-messages"> = {
 	getModels: async () => getModels("anthropic"),
 
 	// shared lazy API implementation (loads the SDK on first request)
-	stream: streamAnthropic,
-	streamSimple: streamSimpleAnthropic,
+	stream: anthropicApi.stream,
+	streamSimple: anthropicApi.streamSimple,
 };
 
 // ---------------------------------------------------------------------------

packages/ai/test/transform-messages-copilot-openai-to-anthropic.test.ts

@@ -1,5 +1,5 @@
 import { describe, expect, it } from "vitest";
-import { transformMessages } from "../src/providers/transform-messages.ts";
+import { transformMessages } from "../src/api/transform-messages.ts";
 import type { AssistantMessage, Message, Model, ToolCall } from "../src/types.ts";
 
 // Normalize function matching what anthropic.ts uses