# 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 `ReadOnly` and `WorkspaceWrite` behavior
- 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)`, and
  `C:\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.
