Revert "Remove Anthropic OAuth support"

This reverts commit f5e6bcac1b.

packages/coding-agent/src/core/auth-storage.ts

@@ -9,6 +9,7 @@
 import {
 	getEnvApiKey,
 	getOAuthApiKey,
+	loginAnthropic,
 	loginAntigravity,
 	loginGeminiCli,
 	loginGitHubCopilot,
@@ -169,6 +170,12 @@ export class AuthStorage {
 		let credentials: OAuthCredentials;
 
 		switch (provider) {
+			case "anthropic":
+				credentials = await loginAnthropic(
+					(url) => callbacks.onAuth({ url }),
+					() => callbacks.onPrompt({ message: "Paste the authorization code:" }),
+				);
+				break;
 			case "github-copilot":
 				credentials = await loginGitHubCopilot({
 					onAuth: (url, instructions) => callbacks.onAuth({ url, instructions }),

packages/coding-agent/src/core/system-prompt.ts

@@ -303,6 +303,5 @@ Documentation:
 	prompt += `\nCurrent date and time: ${dateTime}`;
 	prompt += `\nCurrent working directory: ${resolvedCwd}`;
 
-	prompt = "You are a helpful assistant. Be concise.";
 	return prompt;
 }