refactor(ai): improve error handling and stop reason types

- Add 'aborted' as a distinct stop reason separate from 'error'
- Change AssistantMessage.error to errorMessage for clarity
- Update error event to include reason field ('error' | 'aborted')
- Map provider-specific safety/refusal reasons to 'error' stop reason
- Reorganize utility functions into utils/ directory
- Rename agent.ts to agent-loop.ts for better clarity
- Fix error handling in all providers to properly distinguish abort from error

packages/ai/src/utils/json-parse.ts

@@ -0,0 +1,28 @@
+import { parse as partialParse } from "partial-json";
+
+/**
+ * Attempts to parse potentially incomplete JSON during streaming.
+ * Always returns a valid object, even if the JSON is incomplete.
+ *
+ * @param partialJson The partial JSON string from streaming
+ * @returns Parsed object or empty object if parsing fails
+ */
+export function parseStreamingJson<T = any>(partialJson: string | undefined): T {
+	if (!partialJson || partialJson.trim() === "") {
+		return {} as T;
+	}
+
+	// Try standard parsing first (fastest for complete JSON)
+	try {
+		return JSON.parse(partialJson) as T;
+	} catch {
+		// Try partial-json for incomplete JSON
+		try {
+			const result = partialParse(partialJson);
+			return (result ?? {}) as T;
+		} catch {
+			// If all parsing fails, return empty object
+			return {} as T;
+		}
+	}
+}