`read_particle_params` unconditionally creates `particles::timestamp_dir` even when timestamping is disabled/empty

Summary

Castro::read_particle_params() always calls UtilCreateDirectory(particles::timestamp_dir, 0755) on IO rank, without checking whether timestamp_dir is non-empty or whether tracer timestamping is enabled. If timestamp_dir is empty, this can fail during startup before any particle work is done.

Location

• Source/particles/CastroParticles.cpp:29

Problem Details

Current code:

if (ParallelDescriptor::IOProcessor())
    if (!amrex::UtilCreateDirectory(particles::timestamp_dir, 0755))
        amrex::CreateDirectoryFailed(particles::timestamp_dir);
ParallelDescriptor::Barrier();

But later timestamp writes are guarded with !particles::timestamp_dir.empty(), so directory creation is inconsistent with usage.

Impact

• Possible startup abort when particles::timestamp_dir is empty or unset.
• Unnecessary filesystem operations when timestamp output is not requested.

Suggested Patch

diff --git a/Source/particles/CastroParticles.cpp b/Source/particles/CastroParticles.cpp
--- a/Source/particles/CastroParticles.cpp
+++ b/Source/particles/CastroParticles.cpp
@@
-    if (ParallelDescriptor::IOProcessor())
-        if (!amrex::UtilCreateDirectory(particles::timestamp_dir, 0755))
-            amrex::CreateDirectoryFailed(particles::timestamp_dir);
-    //
-    // Force other processors to wait till directory is built.
-    //
-    ParallelDescriptor::Barrier();
+    if (!particles::timestamp_dir.empty()) {
+        if (ParallelDescriptor::IOProcessor()) {
+            if (!amrex::UtilCreateDirectory(particles::timestamp_dir, 0755)) {
+                amrex::CreateDirectoryFailed(particles::timestamp_dir);
+            }
+        }
+        //
+        // Force other processors to wait till directory is built.
+        //
+        ParallelDescriptor::Barrier();
+    }

Prepared by Codex

Start in Source/particles/CastroParticles.cpp:29 and read Castro::read_particle_params(), including the existing timestamp-directory checks described in the issue. Verify that startup with an empty timestamp_dir avoids directory creation and that configured timestamp output still creates its directory before the barrier.