[mcp-client] Re-inject errors into the LLM (#1511)

Possibly close #1502

---------

Co-authored-by: célina <[email protected]>

Author: julien-c

packages/mcp-client/src/McpClient.ts

@@ -186,8 +186,6 @@ export class McpClient {
 		for (const toolCall of Object.values(finalToolCalls)) {
 			const toolName = toolCall.function.name ?? "unknown";
 			/// TODO(Fix upstream type so this is always a string)^
-			const toolArgs = toolCall.function.arguments === "" ? {} : JSON.parse(toolCall.function.arguments);
-
 			const toolMessage: ChatCompletionInputMessageTool = {
 				role: "tool",
 				tool_call_id: toolCall.id,
@@ -198,11 +196,29 @@ export class McpClient {
 				messages.push(toolMessage);
 				return yield toolMessage;
 			}
+			let toolArgs: Record<string, unknown> = {};
+			try {
+				toolArgs = toolCall.function.arguments === "" ? {} : JSON.parse(toolCall.function.arguments);
+			} catch (error) {
+				if (error instanceof SyntaxError) {
+					toolMessage.content = `Invalid JSON generated by the model: ${error.message}`;
+					messages.push(toolMessage);
+					yield toolMessage;
+					continue;
+				} else {
+					throw error;
+				}
+			}
+
 			/// Get the appropriate session for this tool
 			const client = this.clients.get(toolName);
 			if (client) {
-				const result = await client.callTool({ name: toolName, arguments: toolArgs, signal: opts.abortSignal });
-				toolMessage.content = ResultFormatter.format(result);
+				try {
+					const result = await client.callTool({ name: toolName, arguments: toolArgs, signal: opts.abortSignal });
+					toolMessage.content = ResultFormatter.format(result);
+				} catch (error) {
+					toolMessage.content = `Error: MCP tool call failed with error message: ${error}`;
+				}
 			} else {
 				toolMessage.content = `Error: No session found for tool: ${toolName}`;
 			}