ui : add backend types and constants

Assisted-by: pi:llama.cpp/DeepSeek-V4.1-Flash

tools/ui/src/lib/constants/backend.constants.ts

@@ -0,0 +1,10 @@
+import type { BackendProtocol } from '$lib/types';
+
+/** Id of the built-in backend that points at the server serving this UI. */
+export const LOCAL_BACKEND_ID = 'local';
+
+/** Protocols a configured backend can speak, in display order. */
+export const BACKEND_PROTOCOLS: readonly BackendProtocol[] = ['llama.cpp', 'openai', 'anthropic'];
+
+/** Prefix for generated ids of user-added backends. */
+export const BACKEND_ID_PREFIX = 'backend';

tools/ui/src/lib/constants/index.ts

@@ -4,6 +4,7 @@
 export * from './agentic.constants';
 export * from './api-endpoints.constants';
 export * from './app.constants';
+export * from './backend.constants';
 export * from './chat-tabs.constants';
 export * from './database.constants';
 export * from './reasoning-effort.constants';

tools/ui/src/lib/types/backend.d.ts

@@ -0,0 +1,30 @@
+/**
+ * Backend types.
+ *
+ * A backend is one API endpoint the UI can talk to. The built-in `local`
+ * backend is the llama-server serving the UI. External backends are
+ * user-configured endpoints that speak an OpenAI- or Anthropic-compatible
+ * protocol.
+ */
+
+/** Request/response shape a backend speaks. */
+export type BackendProtocol = 'llama.cpp' | 'openai' | 'anthropic';
+
+/** One configured API endpoint. */
+export interface Backend {
+	/** Bearer token / API key used for this backend. */
+	apiKey?: string;
+	/**
+	 * API root the endpoint paths are appended to, e.g. https://api.example.com.
+	 * Empty for the local backend, which resolves against the UI origin instead.
+	 */
+	baseUrl: string;
+	/** Disabled backends stay configured but are not queried. */
+	enabled: boolean;
+	/** Extra headers merged into every request to this backend. */
+	headers?: Record<string, string>;
+	/** Stable identity. The local backend id is reserved. */
+	id: string;
+	name: string;
+	protocol: BackendProtocol;
+}

tools/ui/src/lib/types/index.ts

@@ -35,6 +35,9 @@ export type {
 	ApiStreamSession
 } from './api';
 
+// Backend types
+export type { Backend, BackendProtocol } from './backend';
+
 // HuggingFace types
 export type {
 	HfCatalogBuild,