feat: redesign sandbox config (#1373)

This is a major redesign of how sandbox configuration works and aims to
fix https://github.com/openai/codex/issues/1248. Specifically, it
replaces `sandbox_permissions` in `config.toml` (and the
`-s`/`--sandbox-permission` CLI flags) with a "table" with effectively
three variants:

```toml
# Safest option: full disk is read-only, but writes and network access are disallowed.
[sandbox]
mode = "read-only"

# The cwd of the Codex task is writable, as well as $TMPDIR on macOS.
# writable_roots can be used to specify additional writable folders.
[sandbox]
mode = "workspace-write"
writable_roots = []  # Optional, defaults to the empty list.
network_access = false  # Optional, defaults to false.

# Disable sandboxing: use at your own risk!!!
[sandbox]
mode = "danger-full-access"
```

This should make sandboxing easier to reason about. While we have
dropped support for `-s`, the way it works now is:

- no flags => `read-only`
- `--full-auto` => `workspace-write`
- currently, there is no way to specify `danger-full-access` via a CLI
flag, but we will revisit that as part of
https://github.com/openai/codex/issues/1254

Outstanding issue:

- As noted in the `TODO` on `SandboxPolicy::is_unrestricted()`, we are
still conflating sandbox preferences with approval preferences in that
case, which needs to be cleaned up.

codex-rs/common/src/approval_mode_cli_arg.rs

@@ -1,13 +1,9 @@
 //! Standard type to use with the `--approval-mode` CLI option.
 //! Available when the `cli` feature is enabled for the crate.
 
-use clap::ArgAction;
-use clap::Parser;
 use clap::ValueEnum;
 
-use codex_core::config::parse_sandbox_permission_with_base_path;
 use codex_core::protocol::AskForApproval;
-use codex_core::protocol::SandboxPermission;
 
 #[derive(Clone, Copy, Debug, ValueEnum)]
 #[value(rename_all = "kebab-case")]
@@ -36,38 +32,3 @@ impl From<ApprovalModeCliArg> for AskForApproval {
         }
     }
 }
-
-#[derive(Parser, Debug)]
-pub struct SandboxPermissionOption {
-    /// Specify this flag multiple times to specify the full set of permissions
-    /// to grant to Codex.
-    ///
-    /// ```shell
-    /// codex -s disk-full-read-access \
-    ///       -s disk-write-cwd \
-    ///       -s disk-write-platform-user-temp-folder \
-    ///       -s disk-write-platform-global-temp-folder
-    /// ```
-    ///
-    /// Note disk-write-folder takes a value:
-    ///
-    /// ```shell
-    ///     -s disk-write-folder=$HOME/.pyenv/shims
-    /// ```
-    ///
-    /// These permissions are quite broad and should be used with caution:
-    ///
-    /// ```shell
-    ///     -s disk-full-write-access
-    ///     -s network-full-access
-    /// ```
-    #[arg(long = "sandbox-permission", short = 's', action = ArgAction::Append, value_parser = parse_sandbox_permission)]
-    pub permissions: Option<Vec<SandboxPermission>>,
-}
-
-/// Custom value-parser so we can keep the CLI surface small *and*
-/// still handle the parameterised `disk-write-folder` case.
-fn parse_sandbox_permission(raw: &str) -> std::io::Result<SandboxPermission> {
-    let base_path = std::env::current_dir()?;
-    parse_sandbox_permission_with_base_path(raw, base_path)
-}