## Summary
Implements a configurable MCP OAuth callback URL override for `codex mcp
login` and app-server OAuth login flows, including support for non-local
callback endpoints (for example, devbox ingress URLs).
## What changed
- Added new config key: `mcp_oauth_callback_url` in
`~/.codex/config.toml`.
- OAuth authorization now uses `mcp_oauth_callback_url` as
`redirect_uri` when set.
- Callback handling validates the callback path against the configured
redirect URI path.
- Listener bind behavior is now host-aware:
- local callback URL hosts (`localhost`, `127.0.0.1`, `::1`) bind to
`127.0.0.1`
- non-local callback URL hosts bind to `0.0.0.0`
- `mcp_oauth_callback_port` remains supported and is used for the
listener port.
- Wired through:
- CLI MCP login flow
- App-server MCP OAuth login flow
- Skill dependency OAuth login flow
- Updated config schema and config tests.
## Why
Some environments need OAuth callbacks to land on a specific reachable
URL (for example ingress in remote devboxes), not loopback. This change
allows that while preserving local defaults for existing users.
## Backward compatibility
- No behavior change when `mcp_oauth_callback_url` is unset.
- Existing `mcp_oauth_callback_port` behavior remains intact.
- Local callback flows continue binding to loopback by default.
## Testing
- `cargo test -p codex-rmcp-client callback -- --nocapture`
- `cargo test -p codex-core --lib mcp_oauth_callback -- --nocapture`
- `cargo check -p codex-cli -p codex-app-server -p codex-rmcp-client`
## Example config
```toml
mcp_oauth_callback_port = 5555
mcp_oauth_callback_url = "https://<devbox>-<namespace>.gateway.<cluster>.internal.api.openai.org/callback"
