codex-core config loader

This module is the canonical place to load and describe Codex configuration layers (user config, CLI/session overrides, managed config, and MDM-managed preferences) and to produce:

• An effective merged TOML config.
• Per-key origins metadata (which layer “wins” for a given key).
• Per-layer versions (stable fingerprints) used for optimistic concurrency / conflict detection.

Public surface

Exported from codex_core::config_loader:

• load_config_layers_state(codex_home, cwd_opt, cli_overrides, overrides, cloud_requirements) -> ConfigLayerStack
• ConfigLayerStack
  • effective_config() -> toml::Value
  • origins() -> HashMap<String, ConfigLayerMetadata>
  • layers_high_to_low() -> Vec<ConfigLayer>
  • with_user_config(user_config) -> ConfigLayerStack
• ConfigLayerEntry (one layer’s {name, config, version, disabled_reason}; name carries source metadata)
• LoaderOverrides (test/override hooks for managed config sources)
• merge_toml_values(base, overlay) (public helper used elsewhere)

Layering model

Precedence is top overrides bottom:

1. MDM managed preferences (macOS only)
2. System managed config (e.g. managed_config.toml)
3. Session flags (CLI overrides, applied as dotted-path TOML writes)
4. User config (config.toml)

Layers with a disabled_reason are still surfaced for UI, but are ignored when computing the effective config and origins metadata. This is what ConfigLayerStack::effective_config() implements.

Typical usage

Most callers want the effective config plus metadata:

use codex_core::config_loader::{load_config_layers_state, LoaderOverrides};
use codex_utils_absolute_path::AbsolutePathBuf;
use toml::Value as TomlValue;

let cli_overrides: Vec<(String, TomlValue)> = Vec::new();
let cwd = AbsolutePathBuf::current_dir()?;
let layers = load_config_layers_state(
    &codex_home,
    Some(cwd),
    &cli_overrides,
    LoaderOverrides::default(),
    None,
).await?;

let effective = layers.effective_config();
let origins = layers.origins();
let layers_for_ui = layers.layers_high_to_low();

Internal layout

Implementation is split by concern:

• state.rs: public types (ConfigLayerEntry, ConfigLayerStack) + merge/origins convenience methods.
• layer_io.rs: reading config.toml, managed config, and managed preferences inputs.
• overrides.rs: CLI dotted-path overrides → TOML “session flags” layer.
• merge.rs: recursive TOML merge.
• fingerprint.rs: stable per-layer hashing and per-key origins traversal.
• macos.rs: managed preferences integration (macOS only).