Desktop sessions fail with API Error: Connection error when using LiteLLM Anthropic gateway

[lost9999]

Summary

PromptX Desktop session requests fail with:

• API Error: Connection error.

This occurs when using LiteLLM as an Anthropic-format gateway for AgentX / Claude Agent SDK.

Environment

• OS: Windows
• PromptX Desktop: 2.4.0
• PromptX MCP Server: 2.2.1
• Claude Agent SDK: 0.1.77
• LiteLLM Proxy: 1.83.3-nightly
• Node: 22.20.0

Symptom in Desktop

After sending a message in PromptX Desktop, the UI shows:

Error (success)
API Error: Connection error.

Repro

1. Configure PromptX Desktop / AgentX to use LiteLLM via Anthropic-style gateway
2. Open a new session
3. Send a message such as:
   • 激活女娲，我要创建一个角色
4. Observe:
   • API Error: Connection error.

Gateway behavior observed locally

The gateway responds on:

• /v1/messages
• /v1/messages?beta=true

However Claude Agent SDK debug logs show streaming/parser failures such as:

Error streaming, falling back to non-streaming mode: Unexpected event order, got message_start before receiving "message_stop"

and earlier also:

Error streaming, falling back to non-streaming mode: Connection error.

Expected

PromptX Desktop sessions should stream and complete normally through a LiteLLM Anthropic gateway.

Actual

Desktop sessions fail with API Error: Connection error. and Claude Agent SDK appears unable to complete the request flow.

Additional notes

Anthropic's Claude Code gateway docs require gateways to correctly support at least:

• /v1/messages
• /v1/messages/count_tokens
• Anthropic header forwarding
• correct Anthropic SSE/event ordering

This may be a PromptX/AgentX compatibility issue with LiteLLM's Anthropic gateway path rather than a plain local proxy configuration issue.