feat: robust error handling and type safety

Add type-safe error helpers and remove 'as any' casts.

Changes:
- Add isAbortError() helper for checking abort signals
- Add getEventDetail() helper for CustomEvent extraction
- Fix variable naming in isRetryable() (isAborted vs isAbortError)
- Use proper instanceof checks instead of casting
- Add proper interface for normalized response data
- Type-safe tool execution error messages

packages/core/src/utils/index.ts

@@ -101,3 +101,30 @@ export function assert(condition: unknown, message?: string, silent?: boolean):
 		throw new Error(errorMessage)
 	}
 }
+
+/**
+ * Check if an error is an AbortError (from AbortController)
+ * Handles various forms: Error with name 'AbortError', or rawError property
+ */
+export function isAbortError(error: unknown): boolean {
+	if (error instanceof Error && error.name === 'AbortError') return true
+	if (
+		typeof error === 'object' &&
+		error !== null &&
+		'rawError' in error &&
+		(error as { rawError?: Error }).rawError?.name === 'AbortError'
+	)
+		return true
+	return false
+}
+
+/**
+ * Safely extract detail from CustomEvent
+ * @returns The detail object or null if not a CustomEvent
+ */
+export function getEventDetail<T>(event: Event): T | null {
+	if (event instanceof CustomEvent) {
+		return event.detail as T
+	}
+	return null
+}