3 Gotchas I Hit Deploying the Claude Agent SDK to Railway

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. Gotcha 3 : haiku shows up in your API logs, but that's not the model degrading — it's by design. It's used for internal chores. Gotcha 1: bypassPermissions doesn't work in a root container What happened Code that ran fine locally started dying with code 1 the moment I deployed it to Railway — the agent did nothing and just exited. The entire error message was essentially this: Error: Claude Code process exited with code 1 That tells you nothing. The only stack trace was from my app; what the child process (the claude binary) actually said before dying was a complete black box. The cause query() spawns a claude binary internally. That binary refuses --dangerously-skip-permissions (which the SDK calls permissionMode: "bypassPermissions" ) when running as root or under sudo . It's a safety measure — skipping all permission checks as root is far too dangerous. Railway, like many container environments, runs as root by default, so if you've set bypassPermissions you will always hit this. You can't catch it locally if you're running as a normal user. Why there are no logs This is the nasty part. Unless you pass an options.stderr callback, the SDK discards the child process's stderr with "ignore" . In other wor