Long-running upstream skills emit MCP notifications/progress on the SSE stream. Without forwarding, the gateway swallows them and the MCP client (Claude Code, Cursor) aborts the tools/call on its idle timer after ~60s — even though the HTTP stream stays warm. Gateway now passes the SDK's extra.sendNotification through to UpstreamAgent.callTool. Any non-response frame with a method but no id becomes a notification on the client side. Each tools/call carries a progressToken (client-supplied or request-id fallback) so the client can correlate. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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