This PR makes it possible to disable live web search via an enterprise
config even if the user is running in `--yolo` mode (though cached web
search will still be available). To do this, create
`/etc/codex/requirements.toml` as follows:
```toml
# "live" is not allowed; "disabled" is allowed even though not listed explicitly.
allowed_web_search_modes = ["cached"]
```
Or set `requirements_toml_base64` MDM as explained on
https://developers.openai.com/codex/security/#locations.
### Why
- Enforce admin/MDM/`requirements.toml` constraints on web-search
behavior, independent of user config and per-turn sandbox defaults.
- Ensure per-turn config resolution and review-mode overrides never
crash when constraints are present.
### What
- Add `allowed_web_search_modes` to requirements parsing and surface it
in app-server v2 `ConfigRequirements` (`allowedWebSearchModes`), with
fixtures updated.
- Define a requirements allowlist type (`WebSearchModeRequirement`) and
normalize semantics:
- `disabled` is always implicitly allowed (even if not listed).
- An empty list is treated as `["disabled"]`.
- Make `Config.web_search_mode` a `Constrained<WebSearchMode>` and apply
requirements via `ConstrainedWithSource<WebSearchMode>`.
- Update per-turn resolution (`resolve_web_search_mode_for_turn`) to:
- Prefer `Live → Cached → Disabled` when
`SandboxPolicy::DangerFullAccess` is active (subject to requirements),
unless the user preference is explicitly `Disabled`.
- Otherwise, honor the user’s preferred mode, falling back to an allowed
mode when necessary.
- Update TUI `/debug-config` and app-server mapping to display
normalized `allowed_web_search_modes` (including implicit `disabled`).
- Fix web-search integration tests to assert cached behavior under
`SandboxPolicy::ReadOnly` (since `DangerFullAccess` legitimately prefers
`live` when allowed).
a118494323