fix: ensure cwd for conversation and sandbox are separate concerns (#3874)

Previous to this PR, both of these functions take a single `cwd`:


71038381aa/codex-rs/core/src/seatbelt.rs (L19-L25)


71038381aa/codex-rs/core/src/landlock.rs (L16-L23)

whereas `cwd` and `sandbox_cwd` should be set independently (fixed in
this PR).

Added `sandbox_distinguishes_command_and_policy_cwds()` to
`codex-rs/exec/tests/suite/sandbox.rs` to verify this.

codex-rs/cli/src/debug_sandbox.rs

@@ -64,7 +64,6 @@ async fn run_command_under_sandbox(
     sandbox_type: SandboxType,
 ) -> anyhow::Result<()> {
     let sandbox_mode = create_sandbox_mode(full_auto);
-    let cwd = std::env::current_dir()?;
     let config = Config::load_with_cli_overrides(
         config_overrides
             .parse_overrides()
@@ -75,13 +74,29 @@ async fn run_command_under_sandbox(
             ..Default::default()
         },
     )?;
+
+    // In practice, this should be `std::env::current_dir()` because this CLI
+    // does not support `--cwd`, but let's use the config value for consistency.
+    let cwd = config.cwd.clone();
+    // For now, we always use the same cwd for both the command and the
+    // sandbox policy. In the future, we could add a CLI option to set them
+    // separately.
+    let sandbox_policy_cwd = cwd.clone();
+
     let stdio_policy = StdioPolicy::Inherit;
     let env = create_env(&config.shell_environment_policy);
 
     let mut child = match sandbox_type {
         SandboxType::Seatbelt => {
-            spawn_command_under_seatbelt(command, &config.sandbox_policy, cwd, stdio_policy, env)
-                .await?
+            spawn_command_under_seatbelt(
+                command,
+                cwd,
+                &config.sandbox_policy,
+                sandbox_policy_cwd.as_path(),
+                stdio_policy,
+                env,
+            )
+            .await?
         }
         SandboxType::Landlock => {
             #[expect(clippy::expect_used)]
@@ -91,8 +106,9 @@ async fn run_command_under_sandbox(
             spawn_command_under_linux_sandbox(
                 codex_linux_sandbox_exe,
                 command,
-                &config.sandbox_policy,
                 cwd,
+                &config.sandbox_policy,
+                sandbox_policy_cwd.as_path(),
                 stdio_policy,
                 env,
             )