feat(ai): add Radius gateway support

packages/coding-agent/src/core/radius.ts

@@ -0,0 +1,34 @@
+/**
+ * Radius (pi-messages gateway) provider wiring.
+ *
+ * The main Radius provider is a built-in OAuth provider in pi-ai; models are
+ * dynamic, cached on the stored OAuth credential (`gatewayConfig`) and
+ * injected via the OAuth provider's `modifyModels` hook, so startup, /reload,
+ * and registry refreshes work without network access. The catalog refreshes
+ * on login and on every token refresh.
+ *
+ * Additional gateways (e.g. a local dev gateway) can be declared in
+ * models.json with `"oauth": "radius"`; each entry is an independent Radius
+ * instance with its own credentials and catalog.
+ */
+
+import { createRadiusOAuthProvider, registerOAuthProvider } from "@earendil-works/pi-ai/oauth";
+
+export const RADIUS_PROVIDER_ID = "radius";
+
+/**
+ * Register a Radius-style OAuth provider for a custom gateway declared in
+ * models.json (`"oauth": "radius"`). Runs on every models.json load so the
+ * registration survives `resetOAuthProviders()` during registry refreshes.
+ */
+export function registerCustomRadiusOAuthProvider(id: string, name: string | undefined, gateway: string): void {
+	registerOAuthProvider(
+		createRadiusOAuthProvider({
+			id,
+			name: name ?? id,
+			// Tolerate an API base URL: the gateway root is what the OAuth and
+			// config discovery endpoints hang off.
+			gateway: gateway.replace(/\/v1\/?$/u, ""),
+		}),
+	);
+}