## Why
`codex-core` has accumulated config loading, requirements parsing, constraint logic, and config-layer state handling in one large crate. This refactor pulls that cohesive subsystem into a dedicated crate so we can reduce the compile/test surface area of `codex-core` and make future config work more isolated.
This is part of the broader goal of right-sizing crates to reduce monolithic rebuild cost and improve incremental development speed.
## What Changed
### New crate
- Added a new workspace crate: `codex-rs/config` (`codex-config`)
- Added workspace wiring in `codex-rs/Cargo.toml`
- Added dependency from `codex-core` to `codex-config`
### Moved config internals from `core` to `config`
Moved these modules into `codex-config`:
- `core/src/config/constraint.rs` -> `config/src/constraint.rs`
- `core/src/config_loader/cloud_requirements.rs` -> `config/src/config_loader/cloud_requirements.rs`
- `core/src/config_loader/config_requirements.rs` -> `config/src/config_loader/config_requirements.rs`
- `core/src/config_loader/fingerprint.rs` -> `config/src/config_loader/fingerprint.rs`
- `core/src/config_loader/merge.rs` -> `config/src/config_loader/merge.rs`
- `core/src/config_loader/overrides.rs` -> `config/src/config_loader/overrides.rs`
- `core/src/config_loader/requirements_exec_policy.rs` -> `config/src/config_loader/requirements_exec_policy.rs`
- `core/src/config_loader/state.rs` -> `config/src/config_loader/state.rs`
### Removed shim modules in `core`
After the move, the temporary one-line `pub use` shim files under `core/src/config_loader/` were deleted so history is a clean move/delete rather than introducing extra permanent forwarding modules.
`core/src/config_loader/mod.rs` now imports/re-exports directly from `codex_config`, including direct use of `build_cli_overrides_layer` and test-only access to `version_for_toml`.
### Follow-on fixes for direct imports
- Updated `core/src/config_loader/macos.rs` to use `super::{ConfigRequirementsToml, ConfigRequirementsWithSources, RequirementSource}`.
- Updated `core/src/config_loader/tests.rs` imports to reference `crate::config_loader` re-exports and `codex_config` exec-policy TOML types.
## Behavior and API Notes
- Config behavior is intended to be unchanged.
- `codex-core` continues to expose the same config-loader-facing API surface to its internal callers via `core/src/config_loader/mod.rs` re-exports.
- The main functional change is crate ownership and dependency direction, not config semantics.
## Validation
Ran:
- `cargo test -p codex-config`
- `cargo test -p codex-core --no-run`
- `cargo test -p codex-core config_loader::tests::load_requirements_toml_produces_expected_constraints`
- `cargo test -p codex-core config_loader::tests::requirements_exec_policy_tests::parses_single_prefix_rule_from_raw_toml`
- `just fmt`
- `just fix -p codex-config -p codex-core`
- `just fix -p codex-core`
All listed commands completed successfully in this workspace environment.
