## What changed
- Add `environment_hooks` to `EnvironmentConfig` for hooks from an environment's effective managed requirements. Initialize it empty for inferred thread configurations and report the handler count in debug output.
- Move `HookEventsToml`, `MatcherGroup`, and `HookHandlerConfig` into `codex_protocol::hooks`, with re-exports from `codex_config::hook_config`.
- Validate MCP hook input recursively to reject nulls and integers outside the signed 64-bit range without converting through `toml::Value`.
GitOrigin-RevId: 410506c8e2b89c9519c81d86b44ccd760d751693
