I deployed a Slack bot app built on the Claude Agent SDK to Railway, and immediately hit a string of landmines around the SDK itself. Every one of them was the "the logs don't tell you what's wrong" kind, and the second one in particular ate a lot of my time. Since other people are likely to get stuck in the same spots, I'm writing it down.
This is aimed at junior-to-mid-level devs using @anthropic-ai/claude-agent-sdk (query()) in Node.js.
TL;DR
Gotcha 1: In a root container, bypassPermissions isn't allowed, and the child process dies with code 1. Worse, stderr is swallowed, so you can't see why.
Gotcha 2: stdio MCP servers don't wait for connection by default, so on turn 1 the tool list is empty — and the model "acts out" tool calls and fabricates the results.
