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

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


237f8a11e1/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/cli/src/landlock.rs

@@ -5,7 +5,6 @@
 
 use codex_core::protocol::SandboxPolicy;
 use std::os::unix::process::ExitStatusExt;
-use std::path::PathBuf;
 use std::process;
 use std::process::Command;
 use std::process::ExitStatus;
@@ -15,7 +14,6 @@ use std::process::ExitStatus;
 pub(crate) fn run_landlock(
     command: Vec<String>,
     sandbox_policy: SandboxPolicy,
-    writable_roots: Vec<PathBuf>,
 ) -> anyhow::Result<()> {
     if command.is_empty() {
         anyhow::bail!("command args are empty");
@@ -23,16 +21,7 @@ pub(crate) fn run_landlock(
 
     // Spawn a new thread and apply the sandbox policies there.
     let handle = std::thread::spawn(move || -> anyhow::Result<ExitStatus> {
-        // Apply sandbox policies inside this thread so only the child inherits
-        // them, not the entire CLI process.
-        if sandbox_policy.is_network_restricted() {
-            codex_core::linux::install_network_seccomp_filter_on_current_thread()?;
-        }
-
-        if sandbox_policy.is_file_write_restricted() {
-            codex_core::linux::install_filesystem_landlock_rules_on_current_thread(writable_roots)?;
-        }
-
+        codex_core::linux::apply_sandbox_policy_to_current_thread(sandbox_policy)?;
         let status = Command::new(&command[0]).args(&command[1..]).status()?;
         Ok(status)
     });

codex-rs/cli/src/main.rs

@@ -7,7 +7,7 @@ use std::path::PathBuf;
 
 use clap::ArgAction;
 use clap::Parser;
-use codex_core::SandboxModeCliArg;
+use codex_core::protocol::SandboxPolicy;
 use codex_exec::Cli as ExecCli;
 use codex_repl::Cli as ReplCli;
 use codex_tui::Cli as TuiCli;
@@ -71,9 +71,9 @@ struct SeatbeltCommand {
     #[arg(long = "writable-root", short = 'w', value_name = "DIR", action = ArgAction::Append, use_value_delimiter = false)]
     writable_roots: Vec<PathBuf>,
 
-    /// Configure the process restrictions for the command.
-    #[arg(long = "sandbox", short = 's')]
-    sandbox_policy: SandboxModeCliArg,
+    /// Convenience alias for low-friction sandboxed automatic execution (network-disabled sandbox that can write to cwd and TMPDIR)
+    #[arg(long = "full-auto", default_value_t = false)]
+    full_auto: bool,
 
     /// Full command args to run under seatbelt.
     #[arg(trailing_var_arg = true)]
@@ -86,9 +86,9 @@ struct LandlockCommand {
     #[arg(long = "writable-root", short = 'w', value_name = "DIR", action = ArgAction::Append, use_value_delimiter = false)]
     writable_roots: Vec<PathBuf>,
 
-    /// Configure the process restrictions for the command.
-    #[arg(long = "sandbox", short = 's')]
-    sandbox_policy: SandboxModeCliArg,
+    /// Convenience alias for low-friction sandboxed automatic execution (network-disabled sandbox that can write to cwd and TMPDIR)
+    #[arg(long = "full-auto", default_value_t = false)]
+    full_auto: bool,
 
     /// Full command args to run under landlock.
     #[arg(trailing_var_arg = true)]
@@ -118,18 +118,20 @@ async fn main() -> anyhow::Result<()> {
         Some(Subcommand::Debug(debug_args)) => match debug_args.cmd {
             DebugCommand::Seatbelt(SeatbeltCommand {
                 command,
-                sandbox_policy,
                 writable_roots,
+                full_auto,
             }) => {
-                seatbelt::run_seatbelt(command, sandbox_policy.into(), writable_roots).await?;
+                let sandbox_policy = create_sandbox_policy(full_auto, &writable_roots);
+                seatbelt::run_seatbelt(command, sandbox_policy).await?;
             }
             #[cfg(target_os = "linux")]
             DebugCommand::Landlock(LandlockCommand {
                 command,
-                sandbox_policy,
                 writable_roots,
+                full_auto,
             }) => {
-                landlock::run_landlock(command, sandbox_policy.into(), writable_roots)?;
+                let sandbox_policy = create_sandbox_policy(full_auto, &writable_roots);
+                landlock::run_landlock(command, sandbox_policy)?;
             }
             #[cfg(not(target_os = "linux"))]
             DebugCommand::Landlock(_) => {
@@ -140,3 +142,11 @@ async fn main() -> anyhow::Result<()> {
 
     Ok(())
 }
+
+fn create_sandbox_policy(full_auto: bool, writable_roots: &[PathBuf]) -> SandboxPolicy {
+    if full_auto {
+        SandboxPolicy::new_full_auto_policy_with_writable_roots(writable_roots)
+    } else {
+        SandboxPolicy::new_read_only_policy_with_writable_roots(writable_roots)
+    }
+}

codex-rs/cli/src/seatbelt.rs

@@ -1,13 +1,11 @@
 use codex_core::exec::create_seatbelt_command;
 use codex_core::protocol::SandboxPolicy;
-use std::path::PathBuf;
 
 pub(crate) async fn run_seatbelt(
     command: Vec<String>,
     sandbox_policy: SandboxPolicy,
-    writable_roots: Vec<PathBuf>,
 ) -> anyhow::Result<()> {
-    let seatbelt_command = create_seatbelt_command(command, sandbox_policy, &writable_roots);
+    let seatbelt_command = create_seatbelt_command(command, &sandbox_policy);
     let status = tokio::process::Command::new(seatbelt_command[0].clone())
         .args(&seatbelt_command[1..])
         .spawn()