fix(coding-agent): improve auth setup warnings

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

@@ -0,0 +1,25 @@
+import { join } from "node:path";
+import { getDocsPath } from "../config.js";
+
+const UNKNOWN_PROVIDER = "unknown";
+
+export function getProviderLoginHelp(): string {
+	return [
+		"Use /login to log into a provider via OAuth or API key. See:",
+		`  ${join(getDocsPath(), "providers.md")}`,
+		`  ${join(getDocsPath(), "models.md")}`,
+	].join("\n");
+}
+
+export function formatNoModelsAvailableMessage(): string {
+	return `No models available. ${getProviderLoginHelp()}`;
+}
+
+export function formatNoModelSelectedMessage(): string {
+	return `No model selected.\n\n${getProviderLoginHelp()}\n\nThen use /model to select a model.`;
+}
+
+export function formatNoApiKeyFoundMessage(provider: string): string {
+	const providerDisplay = provider === UNKNOWN_PROVIDER ? "the selected model" : provider;
+	return `No API key found for ${providerDisplay}.\n\n${getProviderLoginHelp()}`;
+}