fix(shared-chat): handle empty tool call arguments in executeTool (#266)

* fix(shared-chat): handle empty tool call arguments in executeTool

When an LLM calls a tool with no parameters (e.g. empty object schema),
some providers stream no argument deltas, leaving the accumulated
arguments as an empty string. `JSON.parse("")` then throws
"Unexpected end of JSON input". Fallback to `'{}'` for empty strings.

* refactor: apply review

---------

Co-authored-by: 藍+85CD <50108258+kwaa@users.noreply.github.com>

packages/shared-chat/src/utils/execute-tool.ts

@@ -32,7 +32,7 @@ export const executeTool = async ({ abortSignal, messages, toolCall, tools }: Ex
   if (toolCall.function.arguments == null)
     throw new Error(`Missing toolCall.function.arguments: ${JSON.stringify(toolCall)}`)
 
-  const parsedArgs = JSON.parse(toolCall.function.arguments) as Record<string, unknown>
+  const parsedArgs = JSON.parse(toolCall.function.arguments.trim() || '{}') as Record<string, unknown>
   const result = wrapToolResult(await tool.execute(parsedArgs, {
     abortSignal,
     messages,