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## Why Codex intentionally ignores unknown `config.toml` fields by default so older and newer config files keep working across versions. That leniency also makes typo detection hard because misspelled or misplaced keys disappear silently. This change adds an opt-in strict config mode so users and tooling can fail fast on unrecognized config fields without changing the default permissive behavior. This feature is possible because `serde_ignored` exposes the exact signal Codex needs: it lets Codex run ordinary Serde deserialization while recording fields Serde would otherwise ignore. That avoids requiring `#[serde(deny_unknown_fields)]` across every config type and keeps strict validation opt-in around the existing config model. ## What Changed ### Added strict config validation - Added `serde_ignored`-based validation for `ConfigToml` in `codex-rs/config/src/strict_config.rs`. - Combined `serde_ignored` with `serde_path_to_error` so strict mode preserves typed config error paths while also collecting fields Serde would otherwise ignore. - Added strict-mode validation for unknown `[features]` keys, including keys that would otherwise be accepted by `FeaturesToml`'s flattened boolean map. - Kept typed config errors ahead of ignored-field reporting, so malformed known fields are reported before unknown-field diagnostics. - Added source-range diagnostics for top-level and nested unknown config fields, including non-file managed preference source names. ### Kept parsing single-pass per source - Reworked file and managed-config loading so strict validation reuses the already parsed `TomlValue` for that source. - For actual config files and managed config strings, the loader now reads once, parses once, and validates that same parsed value instead of deserializing multiple times. - Validated `-c` / `--config` override layers with the same base-directory context used for normal relative-path resolution, so unknown override keys are still reported when another override contains a relative path. ### Scoped `--strict-config` to config-heavy entry points - Added support for `--strict-config` on the main config-loading entry points where it is most useful: - `codex` - `codex resume` - `codex fork` - `codex exec` - `codex review` - `codex mcp-server` - `codex app-server` when running the server itself - the standalone `codex-app-server` binary - the standalone `codex-exec` binary - Commands outside that set now reject `--strict-config` early with targeted errors instead of accepting it everywhere through shared CLI plumbing. - `codex app-server` subcommands such as `proxy`, `daemon`, and `generate-*` are intentionally excluded from the first rollout. - When app-server strict mode sees invalid config, app-server exits with the config error instead of logging a warning and continuing with defaults. - Introduced a dedicated `ReviewCommand` wrapper in `codex-rs/cli` instead of extending shared `ReviewArgs`, so `--strict-config` stays on the outer config-loading command surface and does not become part of the reusable review payload used by `codex exec review`. ### Coverage - Added tests for top-level and nested unknown config fields, unknown `[features]` keys, typed-error precedence, source-location reporting, and non-file managed preference source names. - Added CLI coverage showing invalid `--enable`, invalid `--disable`, and unknown `-c` overrides still error when `--strict-config` is present, including compound-looking feature names such as `multi_agent_v2.subagent_usage_hint_text`. - Added integration coverage showing both `codex app-server --strict-config` and standalone `codex-app-server --strict-config` exit with an error for unknown config fields instead of starting with fallback defaults. - Added coverage showing unsupported command surfaces reject `--strict-config` with explicit errors. ## Example Usage Run Codex with strict config validation enabled: ```shell codex --strict-config ``` Strict config mode is also available on the supported config-heavy subcommands: ```shell codex --strict-config exec "explain this repository" codex review --strict-config --uncommitted codex mcp-server --strict-config codex app-server --strict-config --listen off codex-app-server --strict-config --listen off ``` For example, if `~/.codex/config.toml` contains a typo in a key name: ```toml model = "gpt-5" approval_polic = "on-request" ``` then `codex --strict-config` reports the misspelled key instead of silently ignoring it. The path is shortened to `~` here for readability: ```text $ codex --strict-config Error loading config.toml: ~/.codex/config.toml:2:1: unknown configuration field `approval_polic` | 2 | approval_polic = "on-request" | ^^^^^^^^^^^^^^ ``` Without `--strict-config`, Codex keeps the existing permissive behavior and ignores the unknown key. Strict config mode also validates ad-hoc `-c` / `--config` overrides: ```text $ codex --strict-config -c foo=bar Error: unknown configuration field `foo` in -c/--config override $ codex --strict-config -c features.foo=true Error: unknown configuration field `features.foo` in -c/--config override ``` Invalid feature toggles are rejected too, including values that look like nested config paths: ```text $ codex --strict-config --enable does_not_exist Error: Unknown feature flag: does_not_exist $ codex --strict-config --disable does_not_exist Error: Unknown feature flag: does_not_exist $ codex --strict-config --enable multi_agent_v2.subagent_usage_hint_text Error: Unknown feature flag: multi_agent_v2.subagent_usage_hint_text ``` Unsupported commands reject the flag explicitly: ```text $ codex --strict-config cloud list Error: `--strict-config` is not supported for `codex cloud` ``` ## Verification The `codex-cli` `strict_config` tests cover invalid `--enable`, invalid `--disable`, the compound `multi_agent_v2.subagent_usage_hint_text` case, unknown `-c` overrides, app-server strict startup failure through `codex app-server`, and rejection for unsupported commands such as `codex cloud`, `codex mcp`, `codex remote-control`, and `codex app-server proxy`. The config and config-loader tests cover unknown top-level fields, unknown nested fields, unknown `[features]` keys, source-location reporting, non-file managed config sources, and `-c` validation for keys such as `features.foo`. The app-server test suite covers standalone `codex-app-server --strict-config` startup failure for an unknown config field. ## Documentation The Codex CLI docs on developers.openai.com/codex should mention `--strict-config` as an opt-in validation mode for supported config-heavy entry points once this ships.
codex-core
This crate implements the business logic for Codex. It is designed to be used by the various Codex UIs written in Rust.
Dependencies
Note that codex-core makes some assumptions about certain helper utilities being available in the environment. Currently, this support matrix is:
macOS
Expects /usr/bin/sandbox-exec to be present.
When using the workspace-write sandbox policy, the Seatbelt profile allows
writes under the configured writable roots while keeping .git (directory or
pointer file), the resolved gitdir: target, and .codex read-only.
Network access and filesystem read/write roots are controlled by
SandboxPolicy. Seatbelt consumes the resolved policy and enforces it.
Seatbelt also keeps the legacy default preferences read access
(user-preference-read) needed for cfprefs-backed macOS behavior.
Linux
Expects the binary containing codex-core to run the equivalent of codex sandbox linux (legacy alias: codex debug landlock) when arg0 is codex-linux-sandbox. See the codex-arg0 crate for details.
Legacy SandboxPolicy / sandbox_mode configs are still supported on Linux.
They can continue to use the legacy Landlock path when the split filesystem
policy is sandbox-equivalent to the legacy model after cwd resolution.
Split filesystem policies that need direct FileSystemSandboxPolicy
enforcement, such as read-only or denied carveouts under a broader writable
root, automatically route through bubblewrap. The legacy Landlock path is used
only when the split filesystem policy round-trips through the legacy
SandboxPolicy model without changing semantics. That includes overlapping
cases like /repo = write, /repo/a = none, /repo/a/b = write, where the
more specific writable child must reopen under a denied parent.
The Linux sandbox helper prefers the first bwrap found on PATH outside the
current working directory whenever it is available. If bwrap is present but
too old to support --argv0, the helper keeps using system bubblewrap and
switches to a no---argv0 compatibility path for the inner re-exec. If
bwrap is missing, it falls back to the bundled codex-resources/bwrap
binary shipped with Codex and Codex surfaces a startup warning through its
normal notification path instead of printing directly from the sandbox helper.
Codex also surfaces a startup warning when bubblewrap cannot create user
namespaces. WSL2 uses the normal Linux bubblewrap path. WSL1 is not supported
for bubblewrap sandboxing because it cannot create the required user
namespaces, so Codex rejects sandboxed shell commands that would enter the
bubblewrap path before invoking bwrap.
Windows
Legacy SandboxPolicy / sandbox_mode configs are still supported on
Windows. Legacy read-only and workspace-write policies imply full
filesystem read access; exact readable roots are represented by split
filesystem policies instead.
The elevated Windows sandbox also supports:
- legacy
ReadOnlyandWorkspaceWritebehavior - split filesystem policies that need exact readable roots, exact writable roots, or extra read-only carveouts under writable roots
- backend-managed system read roots required for basic execution, such as
C:\Windows,C:\Program Files,C:\Program Files (x86), andC:\ProgramData, when a split filesystem policy requests platform defaults
The unelevated restricted-token backend still supports the legacy full-read
Windows model for legacy ReadOnly and WorkspaceWrite behavior. It also
supports a narrow split-filesystem subset: full-read split policies whose
writable roots still match the legacy WorkspaceWrite root set, but add extra
read-only carveouts under those writable roots.
New [permissions] / split filesystem policies remain supported on Windows
only when they can be enforced directly by the selected Windows backend or
round-trip through the legacy SandboxPolicy model without changing semantics.
Policies that would require direct explicit unreadable carveouts (none) or
reopened writable descendants under read-only carveouts still fail closed
instead of running with weaker enforcement.
All Platforms
Expects the binary containing codex-core to simulate the virtual
apply_patch CLI when arg1 is --codex-run-as-apply-patch. See the
codex-arg0 crate for details.