Error responses expose internal error context to clients

[aram356]

Summary

user_message() returns the Display representation of TrustedServerError, which includes internal error context like "Configuration error: ...", "Proxy error: ...". These are returned directly to clients in the response body.

Refs

• crates/fastly/src/error.rs lines 17-18

Recommendation

Return generic error messages to clients; keep detailed context in server logs only.

Context

Production readiness audit — see #396