feat: custom tool renderers

utils/tool-errors.ts

@@ -0,0 +1,36 @@
+import type { JSONValue } from "ai";
+
+export type ToolErrorOutput =
+    | { type: "error-text"; value: string }
+    | { type: "error-json"; value: JSONValue };
+
+export const serializeToolError = (error: unknown): string => {
+    if (error instanceof Error) {
+        return error.message;
+    }
+    if (typeof error === "string") {
+        return error;
+    }
+    try {
+        return JSON.stringify(error) ?? "An unknown tool error occurred";
+    } catch {
+        return "The tool returned an error that could not be serialized";
+    }
+};
+
+export const readStoredToolError = (
+    error: Readonly<{ type: string; value: string }> | null | undefined,
+): ToolErrorOutput => {
+    if (!error) {
+        return { type: "error-text", value: "An unknown tool error occurred" };
+    }
+    if (error.type === "json") {
+        try {
+            const value: JSONValue = JSON.parse(error.value);
+            return { type: "error-json", value };
+        } catch {
+            // Older tool failures were saved as JSON even when their value was plain text.
+        }
+    }
+    return { type: "error-text", value: error.value };
+};