The server's 426 body reached the user as "needs \u003e= 0.2.0, \u003c 1.0.0": Go escapes <, > and & by default for JSON destined for a page, which this is not. Disabled at the encoder. The client now parses the error field rather than pattern-matching it, so it survives whatever a future encoder decides to escape. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>