fix: sanitize AbortSignal in V3 plugin callback args before postMessage

[ruyari-cupcake]

Problem

When a V3 plugin registers a provider via addProvider, the callback is never invoked. Instead, the user sees:

Plugin Error from MyProvider: {}

Root Cause

In factory.ts, the deserializeArgs callback proxy passes innerArgs directly to postMessage. When requestPlugin (in request.ts) calls the provider function as v2Function(args, abortSignal), the AbortSignal object is included in innerArgs.

AbortSignal cannot be structured-cloned (per the HTML spec), so postMessage throws a DataCloneError. Since DOMException has non-enumerable properties, JSON.stringify(error) produces {}, resulting in the unhelpful error message.

Fix

Filter AbortSignal to null in the callback args before postMessage:

ypescript const sanitizedArgs = innerArgs.map(arg => arg instanceof AbortSignal ? null : arg );

This is the minimal change needed. The plugin still receives the full request arguments (prompt_chat, mode, max_tokens, etc.) — only the non-cloneable AbortSignal is replaced with null.

Impact

• All V3 plugins using addProvider are currently broken by this bug
• This fix enables V3 plugin providers to work correctly
• No security implications: AbortSignal is a cancellation signal, not sensitive data
• Plugins lose abort/cancel functionality, but gain the ability to function at all