feat(ai): route copilot claude via anthropic messages api

packages/ai/src/providers/anthropic.ts

@@ -28,6 +28,7 @@ import { AssistantMessageEventStream } from "../utils/event-stream.js";
 import { parseStreamingJson } from "../utils/json-parse.js";
 import { sanitizeSurrogates } from "../utils/sanitize-unicode.js";
 
+import { buildCopilotDynamicHeaders, hasCopilotVisionInput } from "./github-copilot-headers.js";
 import { adjustMaxTokensForThinking, buildBaseOptions } from "./simple-options.js";
 import { transformMessages } from "./transform-messages.js";
 
@@ -217,11 +218,22 @@ export const streamAnthropic: StreamFunction<"anthropic-messages", AnthropicOpti
 
 		try {
 			const apiKey = options?.apiKey ?? getEnvApiKey(model.provider) ?? "";
+
+			let copilotDynamicHeaders: Record<string, string> | undefined;
+			if (model.provider === "github-copilot") {
+				const hasImages = hasCopilotVisionInput(context.messages);
+				copilotDynamicHeaders = buildCopilotDynamicHeaders({
+					messages: context.messages,
+					hasImages,
+				});
+			}
+
 			const { client, isOAuthToken } = createClient(
 				model,
 				apiKey,
 				options?.interleavedThinking ?? true,
 				options?.headers,
+				copilotDynamicHeaders,
 			);
 			const params = buildParams(model, context, isOAuthToken, options);
 			options?.onPayload?.(params);
@@ -471,12 +483,54 @@ function isOAuthToken(apiKey: string): boolean {
 	return apiKey.includes("sk-ant-oat");
 }
 
-function createClient(
-	model: Model<"anthropic-messages">,
-	apiKey: string,
-	interleavedThinking: boolean,
-	optionsHeaders?: Record<string, string>,
-): { client: Anthropic; isOAuthToken: boolean } {
+export interface BuildAnthropicClientOptionsParams {
+	model: Model<"anthropic-messages">;
+	apiKey: string;
+	interleavedThinking: boolean;
+	dynamicHeaders?: Record<string, string>;
+	optionsHeaders?: Record<string, string>;
+}
+
+export interface AnthropicClientConfig {
+	apiKey: string | null;
+	authToken?: string;
+	baseURL: string;
+	defaultHeaders: Record<string, string>;
+	dangerouslyAllowBrowser: boolean;
+	isOAuthToken: boolean;
+}
+
+export function buildAnthropicClientOptions(params: BuildAnthropicClientOptionsParams): AnthropicClientConfig {
+	const { model, apiKey, interleavedThinking, dynamicHeaders, optionsHeaders } = params;
+
+	// Copilot: Bearer auth, selective betas
+	if (model.provider === "github-copilot") {
+		const betaFeatures: string[] = [];
+		if (interleavedThinking) {
+			betaFeatures.push("interleaved-thinking-2025-05-14");
+		}
+
+		const defaultHeaders = mergeHeaders(
+			{
+				accept: "application/json",
+				"anthropic-dangerous-direct-browser-access": "true",
+				...(betaFeatures.length > 0 ? { "anthropic-beta": betaFeatures.join(",") } : {}),
+				Authorization: `Bearer ${apiKey}`,
+			},
+			dynamicHeaders,
+			model.headers,
+			optionsHeaders,
+		);
+
+		return {
+			apiKey: null,
+			baseURL: model.baseUrl,
+			defaultHeaders,
+			dangerouslyAllowBrowser: true,
+			isOAuthToken: false,
+		};
+	}
+
 	const betaFeatures = ["fine-grained-tool-streaming-2025-05-14"];
 	if (interleavedThinking) {
 		betaFeatures.push("interleaved-thinking-2025-05-14");
@@ -484,7 +538,6 @@ function createClient(
 
 	const oauthToken = isOAuthToken(apiKey);
 	if (oauthToken) {
-		// Stealth mode: Mimic Claude Code's headers exactly
 		const defaultHeaders = mergeHeaders(
 			{
 				accept: "application/json",
@@ -497,15 +550,14 @@ function createClient(
 			optionsHeaders,
 		);
 
-		const client = new Anthropic({
+		return {
 			apiKey: null,
 			authToken: apiKey,
 			baseURL: model.baseUrl,
 			defaultHeaders,
 			dangerouslyAllowBrowser: true,
-		});
-
-		return { client, isOAuthToken: true };
+			isOAuthToken: true,
+		};
 	}
 
 	const defaultHeaders = mergeHeaders(
@@ -518,14 +570,39 @@ function createClient(
 		optionsHeaders,
 	);
 
-	const client = new Anthropic({
+	return {
 		apiKey,
 		baseURL: model.baseUrl,
-		dangerouslyAllowBrowser: true,
 		defaultHeaders,
+		dangerouslyAllowBrowser: true,
+		isOAuthToken: false,
+	};
+}
+
+function createClient(
+	model: Model<"anthropic-messages">,
+	apiKey: string,
+	interleavedThinking: boolean,
+	optionsHeaders?: Record<string, string>,
+	dynamicHeaders?: Record<string, string>,
+): { client: Anthropic; isOAuthToken: boolean } {
+	const config = buildAnthropicClientOptions({
+		model,
+		apiKey,
+		interleavedThinking,
+		dynamicHeaders,
+		optionsHeaders,
 	});
 
-	return { client, isOAuthToken: false };
+	const client = new Anthropic({
+		apiKey: config.apiKey,
+		...(config.authToken ? { authToken: config.authToken } : {}),
+		baseURL: config.baseURL,
+		defaultHeaders: config.defaultHeaders,
+		dangerouslyAllowBrowser: config.dangerouslyAllowBrowser,
+	});
+
+	return { client, isOAuthToken: config.isOAuthToken };
 }
 
 function buildParams(