## Why
PR #13783 moved the `codex.rs` unit tests into `codex_tests.rs`. This
applies the same extraction pattern across the rest of `codex-rs/core`
so the production modules stay focused on runtime code instead of large
inline test blocks.
Keeping the tests in sibling files also makes follow-up edits easier to
review because product changes no longer have to share a file with
hundreds or thousands of lines of test scaffolding.
## What changed
- replaced each inline `mod tests { ... }` in `codex-rs/core/src/**`
with a path-based module declaration
- moved each extracted unit test module into a sibling `*_tests.rs`
file, using `mod_tests.rs` for `mod.rs` modules
- preserved the existing `cfg(...)` guards and module-local structure so
the refactor remains structural rather than behavioral
## Testing
- `cargo test -p codex-core --lib` (`1653 passed; 0 failed; 5 ignored`)
- `just fix -p codex-core`
- `cargo fmt --check`
- `cargo shear`
Migration Behavior
* Config
* Migrates settings.json into config.toml
* Only adds fields when config.toml is missing, or when those fields are
missing from the existing file
* Supported mappings:
env -> shell_environment_policy
sandbox.enabled = true -> sandbox_mode = "workspace-write"
* Skills
* Copies home and repo .claude/skills into .agents/skills
* Existing skill directories are not overwritten
* SKILL.md content is rewritten from Claude-related terms to Codex
* AgentsMd
* Repo only
* Migrates CLAUDE.md into AGENTS.md
* Detect/import only proceed when AGENTS.md is missing or present but
empty
* Content is rewritten from Claude-related terms to Codex
Michael Bolin