Use codex-linux-sandbox in unified exec (#6480)

Unified exec isn't working on Linux because we don't provide the correct
arg0.

The library we use for pty management doesn't allow setting arg0
separately from executable. Use the same aliasing strategy we use for
`apply_patch` for `codex-linux-sandbox`.

Use `#[ctor]` hack to dispatch codex-linux-sandbox calls.


Addresses https://github.com/openai/codex/issues/6450

codex-rs/core/tests/suite/mod.rs

@@ -1,4 +1,17 @@
 // Aggregates all former standalone integration tests as modules.
+use codex_arg0::arg0_dispatch;
+use ctor::ctor;
+use tempfile::TempDir;
+
+// This code runs before any other tests are run.
+// It allows the test binary to behave like codex and dispatch to apply_patch and codex-linux-sandbox
+// based on the arg0.
+// NOTE: this doesn't work on ARM
+#[ctor]
+pub static CODEX_ALIASES_TEMP_DIR: TempDir = unsafe {
+    #[allow(clippy::unwrap_used)]
+    arg0_dispatch().unwrap()
+};
 
 #[cfg(not(target_os = "windows"))]
 mod abort_tasks;