codex: support hooks in config.toml and requirements.toml (#18893)

## Summary

Support the existing hooks schema in inline TOML so hooks can be
configured from both `config.toml` and enterprise-managed
`requirements.toml` without requiring a separate `hooks.json` payload.

This gives enterprise admins a way to ship managed hook policy through
the existing requirements channel while still leaving script delivery to
MDM or other device-management tooling, and it keeps `hooks.json`
working unchanged for existing users.

This also lays the groundwork for follow-on managed filtering work such
as #15937, while continuing to respect project trust gating from #14718.
It does **not** implement `allow_managed_hooks_only` itself.

NOTE: yes, it's a bit unfortunate that the toml isn't formatted as
closely as normal to our default styling. This is because we're trying
to stay compatible with the spec for plugins/hooks that we'll need to
support & the main usecase here is embedding into requirements.toml

## What changed

- moved the shared hook serde model out of `codex-rs/hooks` into
`codex-rs/config` so the same schema can power `hooks.json`, inline
`config.toml` hooks, and managed `requirements.toml` hooks
- added `hooks` support to both `ConfigToml` and
`ConfigRequirementsToml`, including requirements-side `managed_dir` /
`windows_managed_dir`
- treated requirements-managed hooks as one constrained value via
`Constrained`, so managed hook policy is merged atomically and cannot
drift across requirement sources
- updated hook discovery to load requirements-managed hooks first, then
per-layer `hooks.json`, then per-layer inline TOML hooks, with a warning
when a single layer defines both representations
- threaded managed hook metadata through discovered handlers and exposed
requirements hooks in app-server responses, generated schemas, and
`/debug-config`
- added hook/config coverage in `codex-rs/config`, `codex-rs/hooks`,
`codex-rs/core/src/config_loader/tests.rs`, and
`codex-rs/core/tests/suite/hooks.rs`

## Testing

- `cargo test -p codex-config`
- `cargo test -p codex-hooks`
- `cargo test -p codex-app-server config_api`

## Documentation

Companion updates are needed in the developers website repo for:

- the hooks guide
- the config reference, sample, basic, and advanced pages
- the enterprise managed configuration guide

---------

Co-authored-by: Michael Bolin <mbolin@openai.com>

codex-rs/app-server/README.md

@@ -209,7 +209,7 @@ Example with notification opt-out:
 - `externalAgentConfig/import` — apply selected external-agent migration items by passing explicit `migrationItems` with `cwd` (`null` for home) and any plugin `details` returned by detect. When a request includes plugin imports, the server emits `externalAgentConfig/import/completed` after the full import finishes (immediately after the response when everything completed synchronously, or after background remote imports finish).
 - `config/value/write` — write a single config key/value to the user's config.toml on disk.
 - `config/batchWrite` — apply multiple config edits atomically to the user's config.toml on disk, with optional `reloadUserConfig: true` to hot-reload loaded threads.
-- `configRequirements/read` — fetch loaded requirements constraints from `requirements.toml` and/or MDM (or `null` if none are configured), including allow-lists (`allowedApprovalPolicies`, `allowedSandboxModes`, `allowedWebSearchModes`), pinned feature values (`featureRequirements`), `enforceResidency`, and `network` constraints such as canonical domain/socket permissions plus `managedAllowedDomainsOnly`.
+- `configRequirements/read` — fetch loaded requirements constraints from `requirements.toml` and/or MDM (or `null` if none are configured), including allow-lists (`allowedApprovalPolicies`, `allowedSandboxModes`, `allowedWebSearchModes`), pinned feature values (`featureRequirements`), managed lifecycle hooks (`hooks`), `enforceResidency`, and `network` constraints such as canonical domain/socket permissions plus `managedAllowedDomainsOnly` and `dangerFullAccessDenylistOnly`.
 
 ### Example: Start or resume a thread