feat(appkit): agent chat UI primitives

Signed-off-by: Hubert Zub <hubert.zub@databricks.com>

Author: hubertzub-db

apps/dev-playground/client/src/lib/agent-chat.ts

@@ -0,0 +1,20 @@
+import type { UIMessage } from "ai";
+
+// Must be a `type` (not `interface`) to satisfy the AI SDK's
+// `UIDataTypes = Record<string, unknown>` constraint.
+export type AgentDataParts = {
+  "approval-pending": {
+    approvalId: string;
+    streamId: string;
+    toolName: string;
+    args: unknown;
+    annotations?: {
+      effect?: "read" | "write" | "update" | "destructive";
+      readOnly?: boolean;
+      destructive?: boolean;
+      idempotent?: boolean;
+    };
+  };
+};
+
+export type AgentUIMessage = UIMessage<unknown, AgentDataParts>;