## What changed
Add `codex tcp-tunnel --diagnostics-json` to emit versioned, newline-delimited JSON diagnostics on stderr. Records classify startup, CONNECT, transport, and control failures without exposing credentials, addresses, headers, or raw error messages. Rejected CONNECT records may include a validated `http_status`.
Distinguish terminal failures from recoverable stream and transport events, flush terminal records before returning a generic error, and preserve stdout readiness and credential acknowledgments. Keep human-readable diagnostics as the default and document the version 1 schema and consumer fallback rules.
## Testing
Add tests for bounded output, error-chain suppression, terminal flushing, control error classification, CONNECT status validation, legacy behavior, and flag parsing. Extend the reconnect test to exercise a rejected CONNECT followed by a successful connection in JSON mode.
GitOrigin-RevId: 350f67fe8e3f313e8a6d3bb0fd891952b77647fd
richardopenai
8d44977aa2