Run sandbox integrity checks before commands and filesystem operations (#51843)

## What changed

Wire existing sandbox integrity checks into local command preparation, exec-server process preparation, and sandboxed filesystem helper and file-open operations. Make execution request preparation asynchronous so callers can await the checks.

The checks remain observational: failures and timeouts do not prevent command execution.

## Testing

Add regression tests that launch a real command after checker preparation fails or exceeds its timeout, verifying successful output and exit status.

GitOrigin-RevId: a82399f8aeb8b08f9965e6121b4c7f460552af3f

codex-rs/exec-server/src/fs_sandbox.rs

@@ -88,6 +88,7 @@ impl FileSystemSandboxRunner {
         request: FsHelperRequest,
     ) -> Result<FsHelperPayload, JSONRPCErrorError> {
         let command = self.sandbox_command(sandbox)?;
+        crate::run_integrity_checks(&command).await;
         let request_json = serde_json::to_vec(&request).map_err(json_error)?;
         run_command(command, request_json).await
     }

codex-rs/exec-server/src/process_sandbox.rs

@@ -298,6 +298,7 @@ pub(crate) async fn prepare_exec_request_with_telemetry(
     }
     .map_err(|err| invalid_params(format!("failed to prepare process sandbox: {err}")))?;
     request.sandbox_override = sandbox_context.sandbox_override;
+    crate::run_integrity_checks(&request).await;
     let windows_sandbox = if sandbox == SandboxType::WindowsRestrictedToken {
         let windows_sandbox_level = windows_sandbox_level.ok_or_else(|| {
             invalid_params("restricted token sandbox requires a sandbox level".to_string())

codex-rs/exec-server/src/sandboxed_file_system.rs

@@ -93,6 +93,7 @@ impl SandboxedFileSystem {
             .sandbox_runner
             .sandbox_command(sandbox)
             .map_err(map_sandbox_error)?;
+        crate::run_integrity_checks(&command).await;
         crate::sandboxed_file_open::open(command, path.clone(), mode)
             .await
             .map_err(map_sandbox_error)