Use cooperative MPI shutdown on parse failure

Remove MPI_Abort() from Main::initialize_() catch block.
All exceptions from readDeck() are synchronized across
ranks via comm.min(), so returning false is safe and lets
Main::~Main() call MPI_Finalize() for cooperative shutdown.

opm/simulators/flow/Main.hpp

@@ -322,15 +322,16 @@ protected:
         // Catch std::exception (not a subclass) because readDeck()
         // may throw std::runtime_error on parse failure while other
         // initialization code may throw std::invalid_argument.
+        // All exceptions here are synchronized across MPI ranks (rank-0-only
+        // exceptions are caught inside readDeck() and converted to a
+        // synchronized throw via comm.min()). Returning false lets
+        // Main::~Main() call MPI_Finalize() for cooperative shutdown.
         catch (const std::exception& e)
         {
             if (outputCout_) {
                 std::cerr << "Failed to create valid EclipseState object." << std::endl;
                 std::cerr << "Exception caught: " << e.what() << std::endl;
             }
-#if HAVE_MPI
-            MPI_Abort(MPI_COMM_WORLD, EXIT_FAILURE);
-#endif
             exitCode = EXIT_FAILURE;
             return false;
         }

opm/simulators/utils/readDeck.cpp

@@ -780,6 +780,10 @@ void Opm::readDeck(Opm::Parallel::Communication    comm,
         errorGuard->clear();
     }
 
+    // Synchronize parse status across all ranks. This serves two purposes:
+    // 1. Propagate rank 0 failure to all ranks (parsing only happens on rank 0)
+    // 2. Ensure all ranks throw together, enabling cooperative shutdown
+    //    via Main::~Main() destructor calling MPI_Finalize()
     parseSuccess = comm.min(parseSuccess);
 
     if (! parseSuccess) {
@@ -789,8 +793,8 @@ void Opm::readDeck(Opm::Parallel::Communication    comm,
 
         // Throw instead of std::exit() so that callers can handle the
         // error. In production, Main::initialize_() catches this and
-        // calls MPI_Abort(). In unit tests, Boost.Test catches it and
-        // reports a proper test failure instead of a silent exit.
+        // returns false for cooperative shutdown. In unit tests,
+        // Boost.Test catches it and reports a proper test failure.
         throw std::runtime_error(failureMessage);
     }
 }