`9.15.0` breaks Cloudflare SDK usage in `sentry-mcp`

[AbhiPrasad]

Description

getsentry/sentry-mcp#136

3:24:55 PM [vite] Internal server error: Cannot read from private field
@sentry/mcp-cloudflare:dev:       at async ProxyServer.fetch (file:///home/dcramer/src/sentry-mcp/node_modules/.pnpm/miniflare@4.20250428.0/node_modules/miniflare/src/workers/core/proxy.worker.ts:173:11)
^C    ...Finishing writing to cache...   

AI summary:

Based on the code and error message, I can identify the issue. The error is occurring because there's a conflict between how Miniflare (the local development environment for Cloudflare Workers) handles private fields and how the Sentry SDK is trying to access them.

This suggests that the issue is related to how Miniflare v4 handles private fields in its proxy implementation, and how the Sentry SDK is trying to access these fields through its proxy wrapper.
Here are a few potential solutions:

1. Update Miniflare to a newer version if available, as this might be a known issue that's been fixed.
2. Modify the proxy implementation in the Sentry SDK to handle private fields differently.
3. Use a different approach for wrapping the fetch handler that doesn't rely on accessing private fields.

I think we should try catch it.

[AbhiPrasad]

This is still happening

[AbhiPrasad]

This was introduced with #16126

specifically the transport patch:

sentry-javascript/packages/core/src/mcp-server.ts

Lines 69 to 99 in 7c50cd4

	const patchedTransport = new Proxy(transport, {
	set(target, key, value) {
	if (key === 'onmessage') {
	target[key] = new Proxy(value, {
	apply(onMessageTarget, onMessageThisArg, onMessageArgArray) {
	const [jsonRpcMessage] = onMessageArgArray;
	if (transport.sessionId && isJsonRPCMessageWithRequestId(jsonRpcMessage)) {
	handleTransportOnMessage(transport.sessionId, jsonRpcMessage.id);
	}
	return Reflect.apply(onMessageTarget, onMessageThisArg, onMessageArgArray);
	},
	});
	} else if (key === 'onclose') {
	target[key] = new Proxy(value, {
	apply(onCloseTarget, onCloseThisArg, onCloseArgArray) {
	if (transport.sessionId) {
	handleTransportOnClose(transport.sessionId);
	}
	return Reflect.apply(onCloseTarget, onCloseThisArg, onCloseArgArray);
	},
	});
	} else {
	target[key as keyof MCPTransport] = value;
	}
	return true;
	},
	});
	return Reflect.apply(target, thisArg, [patchedTransport, ...restArgs]);
	},
	});

this is the miniflare code: https://github.com/cloudflare/workers-sdk/blob/f901e14e842b57c90729d6f5c2b308f60323aaba/packages/miniflare/src/workers/core/proxy.worker.ts#L171-L181

and this is the agents code: https://github.com/cloudflare/agents/blob/dc0e8de4d4717c83fa3850853d125cfe047a9443/packages/agents/src/mcp/index.ts#L324

[github-actions]

A PR closing this issue has just been released 🚀

This issue was referenced by PR #16180, which was included in the 9.16.0 release.

[AbhiPrasad]

Created issue w/ cloudflare here: cloudflare/workers-sdk#9169

[AbhiPrasad]

Fix was released with cloudflare/workers-sdk#9169 (comment)

We need to bump sentry-mcp to validate.