fix: clamp t_stop for adaptive-dt examples with reduced timesteps

Post_process computes the number of save files from t_stop/t_save.
With t_step_stop=25, the simulation produces fewer saves than the
original t_stop implies, causing 'lustre_N.dat is missing' errors.
Clamp t_stop = t_save so post_process only reads saves that exist.

Author: sbryngelson

toolchain/mfc/test/cases.py

@@ -1566,6 +1566,12 @@ def modify_example_case(case: dict):
                     case["t_step_stop"] = 25
                     case["t_step_save"] = 25
 
+                # Adaptive-dt examples: clamp t_stop so post_process
+                # only reads save files that actually exist.
+                if case.get("cfl_adap_dt", "F") == "T":
+                    t_save = float(case.get("t_save", 1.0))
+                    case["t_stop"] = t_save
+
                 caseSize = case["m"] * max(case["n"], 1) * max(case["p"], 1)
                 if caseSize > 25 * 25:
                     if case["n"] == 0 and case["p"] == 0: