fix: overhaul SandboxPolicy and config loading in Rust (#732)

Previous to this PR, `SandboxPolicy` was a bit difficult to work with:


https://github.com/openai/codex/blob/237f8a11e11fdcc793a09e787e48215676d9b95b/codex-rs/core/src/protocol.rs#L98-L108

Specifically:

* It was an `enum` and therefore options were mutually exclusive as
opposed to additive.
* It defined things in terms of what the agent _could not_ do as opposed
to what they _could_ do. This made things hard to support because we
would prefer to build up a sandbox config by starting with something
extremely restrictive and only granting permissions for things the user
as explicitly allowed.

This PR changes things substantially by redefining the policy in terms
of two concepts:

* A `SandboxPermission` enum that defines permissions that can be
granted to the agent/sandbox.
* A `SandboxPolicy` that internally stores a `Vec<SandboxPermission>`,
but externally exposes a simpler API that can be used to configure
Seatbelt/Landlock.

Previous to this PR, we supported a `--sandbox` flag that effectively
mapped to an enum value in `SandboxPolicy`. Though now that
`SandboxPolicy` is a wrapper around `Vec<SandboxPermission>`, the single
`--sandbox` flag no longer makes sense. While I could have turned it
into a flag that the user can specify multiple times, I think the
current values to use with such a flag are long and potentially messy,
so for the moment, I have dropped support for `--sandbox` altogether and
we can bring it back once we have figured out the naming thing.

Since `--sandbox` is gone, users now have to specify `--full-auto` to
get a sandbox that allows writes in `cwd`. Admittedly, there is no clean
way to specify the equivalent of `--full-auto` in your `config.toml`
right now, so we will have to revisit that, as well.

Because `Config` presents a `SandboxPolicy` field and `SandboxPolicy`
changed considerably, I had to overhaul how config loading works, as
well. There are now two distinct concepts, `ConfigToml` and `Config`:

* `ConfigToml` is the deserialization of `~/.codex/config.toml`. As one
might expect, every field is `Optional` and it is `#[derive(Deserialize,
Default)]`. Consistent use of `Optional` makes it clear what the user
has specified explicitly.
* `Config` is the "normalized config" and is produced by merging
`ConfigToml` with `ConfigOverrides`. Where `ConfigToml` contains a raw
`Option<Vec<SandboxPermission>>`, `Config` presents only the final
`SandboxPolicy`.

The changes to `core/src/exec.rs` and `core/src/linux.rs` merit extra
special attention to ensure we are faithfully mapping the
`SandboxPolicy` to the Seatbelt and Landlock configs, respectively.

Also, take note that `core/src/seatbelt_readonly_policy.sbpl` has been
renamed to `codex-rs/core/src/seatbelt_base_policy.sbpl` and that
`(allow file-read*)` has been removed from the `.sbpl` file as now this
is added to the policy in `core/src/exec.rs` when
`sandbox_policy.has_full_disk_read_access()` is `true`.

codex-rs/tui/src/cli.rs

@@ -1,6 +1,5 @@
 use clap::Parser;
 use codex_core::ApprovalModeCliArg;
-use codex_core::SandboxModeCliArg;
 use std::path::PathBuf;
 
 #[derive(Parser, Debug)]
@@ -21,11 +20,9 @@ pub struct Cli {
     #[arg(long = "ask-for-approval", short = 'a')]
     pub approval_policy: Option<ApprovalModeCliArg>,
 
-    /// Configure the process restrictions when a command is executed.
-    ///
-    /// Uses OS-specific sandboxing tools; Seatbelt on OSX, landlock+seccomp on Linux.
-    #[arg(long = "sandbox", short = 's')]
-    pub sandbox_policy: Option<SandboxModeCliArg>,
+    /// Convenience alias for low-friction sandboxed automatic execution (-a on-failure, network-disabled sandbox that can write to cwd and TMPDIR)
+    #[arg(long = "full-auto", default_value_t = false)]
+    pub full_auto: bool,
 
     /// Allow running Codex outside a Git repository.
     #[arg(long = "skip-git-repo-check", default_value_t = false)]
@@ -34,12 +31,4 @@ pub struct Cli {
     /// Disable server‑side response storage (sends the full conversation context with every request)
     #[arg(long = "disable-response-storage", default_value_t = false)]
     pub disable_response_storage: bool,
-
-    /// Convenience alias for low-friction sandboxed automatic execution (-a on-failure, -s network-and-file-write-restricted)
-    #[arg(long = "full-auto", default_value_t = true)]
-    pub full_auto: bool,
-
-    /// Convenience alias for supervised sandboxed execution (-a unless-allow-listed, -s network-and-file-write-restricted)
-    #[arg(long = "suggest", default_value_t = false)]
-    pub suggest: bool,
 }

codex-rs/tui/src/lib.rs

@@ -6,6 +6,8 @@
 use app::App;
 use codex_core::config::Config;
 use codex_core::config::ConfigOverrides;
+use codex_core::protocol::AskForApproval;
+use codex_core::protocol::SandboxPolicy;
 use codex_core::util::is_inside_git_repo;
 use log_layer::TuiLogLayer;
 use std::fs::OpenOptions;
@@ -33,12 +35,21 @@ pub use cli::Cli;
 pub fn run_main(cli: Cli) -> std::io::Result<()> {
     assert_env_var_set();
 
+    let (sandbox_policy, approval_policy) = if cli.full_auto {
+        (
+            Some(SandboxPolicy::new_full_auto_policy()),
+            Some(AskForApproval::OnFailure),
+        )
+    } else {
+        (None, cli.approval_policy.map(Into::into))
+    };
+
     let config = {
         // Load configuration and support CLI overrides.
         let overrides = ConfigOverrides {
             model: cli.model.clone(),
-            approval_policy: cli.approval_policy.map(Into::into),
-            sandbox_policy: cli.sandbox_policy.map(Into::into),
+            approval_policy,
+            sandbox_policy,
             disable_response_storage: if cli.disable_response_storage {
                 Some(true)
             } else {