`plotFileOutput` uses inconsistent derive filtering and can overrun `plotMF` components

Summary

Castro::plotFileOutput excludes particle-derived fields (particle_count, total_particle_count) from num_derive when TracerPC is null, but later copies derived data using a different filter that does not apply that exclusion. This can copy extra components beyond the allocated plotMF size.

Location

• Source/driver/Castro_io.cpp:972
• Source/driver/Castro_io.cpp:995
• Source/driver/Castro_io.cpp:1182
• Source/driver/Castro_io.cpp:1186

Problem Details

First pass (num_derive) applies a particles-specific guard:

if (dd.name() == "particle_count" || dd.name() == "total_particle_count") {
    if (Castro::theTracerPC()) {
        num_derive += dd.numDerive();
    }
}

But second pass (copy into plotMF) does not:

if (isDerivePlotVar...) {
    auto derive_dat = derive(...);
    MultiFab::Copy(plotMF, *derive_dat, 0, cnt, dd.numDerive(), nGrow);
    cnt += dd.numDerive();
}

So cnt can exceed n_data_items and write past the intended component range.

Impact

• Potential out-of-bounds component copy into plotMF.
• Plotfile corruption or runtime failure when particle derived fields are requested without an active tracer container.

Suggested Patch

Apply the same particle guard in the copy loop:

diff --git a/Source/driver/Castro_io.cpp b/Source/driver/Castro_io.cpp
--- a/Source/driver/Castro_io.cpp
+++ b/Source/driver/Castro_io.cpp
@@
         for (const auto & dd : dlist) {

             if ((parent->isDerivePlotVar(dd.name()) && is_small == 0) ||
                 (parent->isDeriveSmallPlotVar(dd.name()) && is_small == 1)) {
+#ifdef AMREX_PARTICLES
+                if ((dd.name() == "particle_count" || dd.name() == "total_particle_count") &&
+                    !Castro::theTracerPC()) {
+                    continue;
+                }
+#endif

                 auto derive_dat = derive(dd.variableName(0), cur_time, nGrow);
                 MultiFab::Copy(plotMF, *derive_dat, 0, cnt, dd.numDerive(), nGrow);
                 cnt = cnt + dd.numDerive();
             }
         }

Prepared by Codex

Start in Source/driver/Castro_io.cpp at lines 972, 995, 1182, and 1186. Compare the particle-derived-field filtering used for num_derive with the later copy loop into plotMF, including the AMREX_PARTICLES guard. Done means both passes apply the same filtering so cnt cannot exceed the allocated component range.